UCSC ON HEARING AND PERCEPTION 

The operation of the ear has two facets: the behavior of the mechanical apparatus and the neurological processing of the information acquired. The mechanics of hearing are straightforward and well understood, but the action of the brain in interpreting sounds is still a matter of dispute among researchers.



Fig. 1 Parts of the ear

1. Auditory canal 6. Round window
2. Ear drum  7. Oval window
3. Hammer  8. Semicircular canals
4. Anvil  9. Cochlea
5. Stirrup  10. Eustachian tube

THE EAR MECHANISM

The ear contains three sections, the outer, middle, and inner ears. The outer ear consists of the lobe and ear canal, structures which serve to protect the more delicate parts inside.
The outer boundry of the middle ear is the eardrum, a thin membrane which vibrates in sympathy with any entering sound. The motion of the eardrum is transferred across the middle ear via three small bones named the hammer, anvil, and stirrup. These bones are supported by muscles which normally allow free motion but can tighten up and inhibit the bones' action when the sound gets too loud. The leverages of these bones are such that rather small motions of the ear drum are very efficiently transmitted.
The boundry of the inner ear is the oval window, another thin membrane which is almost totally covered by the end of the stirrup. The inner ear is not a chamber like the middle ear, but consists of several tubes which wind in various ways within the skull. Most of these tubes, the ones called the semicircular canals, are part of our orientation apparatus. (They contain fine particles of dust-the location of the dust tells us which way is up.) The tube involved in the hearing process is wound tightly like a snail shell and is called the cochlea.


Fig 2. Schematic of the ear
This is a diagram of the ear with the cochlea unwound. The cochlea is filled with fluid and is divided in two the long way by the basilar membrane. The basilar membrane is supported by the sides of the cochlea but is not tightly stretched. Sound introduced into the cochlea via the oval window flexes the basilar membrane and sets up traveling waves along its length. The taper of the membrane is such that these traveling waves are not of even amplitude the entire distance, but grow in amplitude to a certain point and then quickly fade out. The point of maximum amplitude depends on the frequency of the sound wave.
The basilar membrane is covered with tiny hairs, and each hair follicle is connected to a bundle of nerves. Motion of the basilar membrane bends the hairs which in turn excite the associated nerve fibers. These fibers carry the sound information to the brain. This information has two components. First, even though a single nerve cell cannot react fast enough to follow audio frequencies, enough cells are involved that the aggregate of all the firing patterns is a fair replica of the waveform. Second, and probably most importantly, the location of the hair cells associated with the firing nerves is highly correlated with the frequency of the sound. A complex sound will produce a series of active loci along the basilar membrane that accurately matches the spectral plot of the sound.
The amplitude of a sound determines how many nerves associated with the appropriate location fire, and to a slight extent the rate of firing. The main effect is that a loud sound excites nerves along a fairly wide region of the basilar membrane, whereas a soft one excites only a few nerves at each locus.

PERCEPTION

The mechanical process described so far is only the beginning of our perception of sounds. The mechanisms of sound interpretation are poorly understood, in fact is not yet clear whether all people interpret sounds in the same way. Until recently, there has been no way to trace the wiring of the brain, no way to apply simple stimuli and see which parts of the nervous system respond, at least not in any detail. The only research method available was to have people listen to sounds and describe what they heard. The variability of listening skills and the imprecision of the language combined to make psycho-acoustics a rather frustrating field of study. Some of the newest research tools show promise of improving the situation, so research that is happening now will likely clear up several of the mysteries.
The current best guess as to the neural operation of hearing goes like this:
We have seen that sound of a particular waveform and frequency sets up a characteristic pattern of active locations on the basilar membranes. (We might assume that the brain deals with these patterns in the same way it deals with visual patterns on the retina.) If a pattern is repeated enough we learn to recognize that pattern as belonging to a certain sound, much as we learn a particular visual pattern belongs to a certain face. (This learning is accomplished most easily during the early years of life.) The absolute position of the pattern is not very important, it is the pattern itself that is learned. We do possess an ability to interpret the location of the pattern to some degree, but that ability is quite variable from one person to the next. (It is not clear whether that ability is innate or learned.) What use the brain makes of the fact that the aggregate firing of the nerves more or less approximates the waveform of the sound is not known. The processing of impulse sounds (which do not last long enough to set up basilar patterns) is also not well explored.

INTERPRETATION OF SOUNDS

Most studies in psycho-acoustics deal with the sensitivity and accuracy of hearing. This data was intended for use in medicine and telecommunications, so it reflects the abilities of the average untrained listener. It seems to be traditional to weed out musicians from such studies, so the capabilities of trained ears are not documented. I suspect such capabilities are much better than that suggested by the classic studies.

LOUDNESS

The ear can respond to a remarkable range of sound amplitude. (Amplitude corresponds to the quality known as loudness.) The ratio between the threshold of pain and the threshold of sensation is on the order of 130 dB, or ten trillion to one. The judgment of relative sounds is more or less logarithmic, such that a tenfold increase in sound power is described as "twice as loud". The just noticeable difference in loudness varies from 3 dB at the threshold of hearing to an impressive 0.5 dB for loud sounds.

Fig. 3 Perceived loudness of sounds
The sensation of loudness is affected by the frequency of the sound. A series of tests using sine waves produces the curves shown. At the low end of the frequency range of hearing, the ear becomes less sensitive to soft sounds, although the pain threshold as well as judgments of relatively loud sounds are not affected much. Sounds of intermediate softness show some but not all of the sensitivity loss indicated for the threshold of hearing. At high frequencies the change in the sensitivity is more abrupt, with sensation ceasing entirely around 20 khz. The threshold of pain increases in the top octave also.
The ability to make loudness judgments is compromised for sounds of less than 200ms duration. Below that limit, the loudness is affected by the length of the sound; shorter is softer. Durations longer than 200ms do not affect loudness judgment, beyond the fact that we tend to stop paying attention to long unchanging tones.

MASKING

The threshold of hearing for a particular tone can be raised by the presence of another noise or another tone. White noise reduces the loudness of all tones, regardless of absolute level. If the bandwidth of the masking noise is reduced, the effect of masking loud tones is reduced, but the threshold of hearing for those tones remains high. If the masking sound is narrow band noise or a tone, masking depends on the frequency relationship of the masked and masking tones. At low loudness levels, a band of noise will mask tones of higher frequency than the noise more than those of lower frequency. At high levels, a band of noise will also mask tones of lower frequency than itself.

PITCH

People's ability to judge pitch is quite variable. (Pitch is the quality of sound associated with frequency.) Most subjects studied could match pitches very well, usually getting the frequencies of two sine waves within 3%. (Musicians can match frequencies to 1%, or should be able to.) Better results are obtained if the stimuli are similar complex tones, which makes sense since there are more active points along the basilar membrane to give clues. Dissimilar complex tones are apparently fairly difficult to match for pitch (judging from experience with ear training students; I haven't seen any studies on the matter to compare them with sine tone results).
Judgment of relative pitch intervals is extremely variable. The notion of the two to one frequency ratio for the octave is probably learned, although it is easily learned given access to a musical instrument. An untrained subject, asked to set the frequency of a tone to twice that of a reference, is quite likely to set them a twelfth or two octaves apart or find some arbitrary and inconsistent ratio. The tendency to land on "proper" intervals increases if complex tones are used instead of sine tones. Trained musicians often produce octaves slightly wider than two to one, although the practical aspects of their instrument strongly influence their sense of interval. (As a bassoonist who has played the same instrument for twenty years, I have a very strong tendency to place G below middle C a bit high.)
Identification of intervals is even more variable, even among musicians. It does appear to be trainable, suggesting it is a learned ability. Identification of exact pitches is so rare that it has not been properly studied, but there is some anecdotal evidence (such as its relatively more common occurrence among people blind from birth) suggesting it is somehow learned also.
The amplitude of sound does not have a strong effect on the perception of pitch. Such effects seem to hold only for sine tones. At low loudness levels pitch recognition of pure tones becomes difficult, and at high levels increasing loudness seems to shift low and middle register pitches down and high register pitches up.
The assignment of the quality of possessing pitch in the first place depends on the duration and spectral content of the sound. If a sound is shorter than 200ms or so, pitch assignment becomes difficult with decreasing length until a sound of 50ms or less can only be described as a pop. Sounds with waveforms fitting the harmonic pattern are clearly heard as pitched, even if the frequencies are offset by some additive factor. As the spectral plot deviates from the harmonic model, the sense of pitch is reduced, although even noise retains some sense of being high or low.

TIMBRE

Recognition of sounds that are similar in aspects other than pitch and loudness is not well studied, but it is an ability that everyone seems to share. We do know that timbre identification depends strongly on two things, waveform of the steady part of the tone, and the way the spectrum changes with time, particularly at the onset or attack. This ability is probably built on pattern matching, a process that is well documented with vision. Once we have learned to identify a particular timbre, recognition is possible even if the pitch is changed or if parts of the spectrum are filtered out. (We are good enough at this that we can tell the pitch of low sounds when played through a sound system that does not reproduce the fundamentals.)

LOCALIZATION

We are also able to perceive the direction of a sound source with some accuracy. Left and right location is determined by perception of the difference of arrival time or difference in phase of sounds at each ear. If there are more than two arrivals, as in a reverberant environment, we choose the direction of the first sound to arrive, even if later ones are louder. Localization is most accurate with high frequency sounds with sharp attacks.
Height information is provided by the shape of our ears. If a sound of fairly high frequency arrives from the front, a small amount of energy is reflected from the back edge of the ear lobe. This reflection is out of phase for one specific frequency, so a notch is produced in the spectrum. The elongated shape of the lobe causes the notch frequency to vary with the vertical angle of incidence, and we can interpret that effect as height. Height detection is not good for sounds originating to the side or back, or lacking high frequency content.


*Sources*
http://artsites.ucsc.edu/EMS/Music/tech_background/TE-03/teces_03.html
http://www.ItchyTastyRecords.com

UCSC on acoustic treatment for the home studio 

ACOUSTIC TREATMENT FOR HOME STUDIOS

Part 1: Soundproofing

Silence is golden, or at least pretty expensive. Commercial recording studios cost hundreds of thousands of dollars to build because they must allow absolutely no sound to enter from a usually noisy urban environment. Double and triple walls, isolated concrete slabs, custom steel doors are all standard but high priced items used in their construction. A studio's sound is its number one asset and most owners will go to any lengths to get it right.

Luckily, electronic music does not normally require the extreme isolation needed for recording live ensembles. The use of microphones is infrequent enough that it can be scheduled for predictably quiet times, and close mic techniques, (which are usually appropriate for sampling or vocal lines) don't pick up much noise. Given a reasonably quiet, solidly built house to start with, a decent home studio can be created with modest expense and effort.

Some Theory

Sound can travel through any medium-- in fact it passes through solids better than through air. Sound intensity is reduced in the transition from one material to another, as from the air to a wall and back. The amount of reduction (called the transmission loss) is related to the density of the wall-- as long as it doesn't move in response to the sound. Unfortunately, all walls are somewhat flexible. Any motion caused by sound striking one side of the wall will result in sound radiated by the other side, an effect called coupling. If the sound hits a resonant frequency, the wall will boom like a drum. Most isolation techniques are really ways to reduce coupling and prevent resonances.

New Construction

The most effective soundproofing must be designed into a house when it is first built. A typical residential wall is made of a frame of 2x4 wood studs covered with 5/8" thick gypsum board. Properly built (no holes!) this will provide about 35 dB of isolation. Fiberglas filler, R-7 or better, will increase this by 5 to 8 dB and decrease wall resonance. Doubling the thickness of gypsum gives another 3 to 6 dB of overall isolation, but its most important effect is lowering the resonant frequency, hopefully below the audio range.

There are two common strategies for reducing coupling between the two sides of the wall. One is to make the gypsum to stud connection springy, either by using metal studs or by hanging the gypboard on resiliant metal bars. The most effective trick is to use separate studs for each face of the wall so there is no direct connection. This eats up a lot of space, but can give a transmission loss of over 60 dB. This is actually better performance than simple cinder block or poured concrete construction!

Fig. 1 Construction Details

These same principles can be applied to floors and ceilings. A heavy false ceiling hung on springs can match the performance of a double wall-- If there is a room below the studio, it should get a double ceiling too.

Interior Windows

The window between control room and studio used to be a traditional feature of a recording facility. The home studio doesn't really need one, because you can get a decent video camera and a large monitor for less than what a good window costs to build. If you want a window, figure 2 shows what has to be done:

Figure 2. The traditional window.

The effectiveness of these kinds of construction depends a great deal on the craftsmanship of the builder. There must be no loose studs, and the sill plates must really hug the floor. The gypboard must be well fitted and all potential cracks must be caulked. (Caulk is soft and will not crack when the building settles.) Do not put holes in sound walls for outlets or pipes-- use surface mount electrical fittings and caulk around any wires that pierce the gypboard.

Structure Born Noise

The peskiest isolation hassle is dealing with sounds transmitted through the frame of the building. The problem is caused by machinery such as air conditioners and refrigerators which are mounted on floors or walls and can actually shake the structure. Footsteps can cause similar effects to a somewhat lesser extent. This is usually not severe with wood frame construction but can be a nightmare in a concrete and steel building.

This kind of noise must be treated at the source. Walking areas should be carpeted, and heavy appliances have to be mounted with shock absorbers or placed on thick rubber pads. In a wooden house sound tends to be transmitted along the floor joists, so some problems can be solved by simply moving the offending machines. With concrete and steel buildings, you usually wind up completely "floating" the studio floor, a very complex and expensive operation.

Water pipes are distressingly efficient at carrying sound. If any pass under the floor of the studio (pipes in the walls are a definite no-no) make sure they are on flexible hangers. If your pipes are prone to "water hammers" consult a plumber about possible cures.

Retrofitting

We seldom have the luxury of building our home studio from scratch. More often we are trying to fix up an existing room, and budget or landlords limit the techniques we can use. The best approach to adding soundproofing is to try simple techniques first and to move to the high caliber options only when needed.

Step One: The Obvious

You can reduce the amount of isolation you need if you give some careful thought to the choice of rooms you are putting your studio in. Pick a room that does not adjoin a kitchen or bathroom, or the place where your housemate does taxes or watches TV. In other words, put some space between the studio and the noisemakers or sound sensitive activities. The fewer walls in common with the rest of the building, the better. Clearly, a house is a better location than an apartment because you don't have to worry as much about sound traveling through the ceiling or floor. An outside corner room away from the street would be a good choice, a basement would be even better.

Some people consider a garage the ideal location for a studio. This may be true, but you will encounter special problems with the big door and with getting heat and ventilation. The way most garages are built, you are really working outdoors.

Step Two: Tighten Up

Most builders are more concerned with how walls look rather than how solid they really are. This is unfortunate, because any air path from one room to another will limit the wall's effectivness. You can make an amazing contribution to keeping the sound in your studio by filling all cracks and holes, no matter how small or indirect.

The worst sound leaks will be around doors. Your neighborhood hardware store has the fittings and gaskets to fill these up, sold for weatherstripping but effective for sound too. Some common styles of gasket are illustrated in fig.3.

Fig. 3 Gaskets

The flat rubber type is used in a door that doesn't fit well, rubber and metal gaskets work on doors that are pretty tight already. The brush material is for sliding surfaces. Don't forget the bottom of the door-- the best gaskets are spring loaded and drop down when the door is closed.

Once the door is sealed there still may be leaks around the door frame. Carefully remove the trim and fill any gap between the frame and gypsum board with caulk or spray polystyrene foam. As long as you are pulling off trim, check for gaps behind the baseboards and around any window frames.

Incidentally, many interior doors are hollow and light and don't really stop sound well even when tightly gasketed. Such a door should be replaced with a solid one. Manufacturers will supply data on the amount of transmission loss a door can provide. Alternatively, the door can be reinforced with a layer of thick plywood, or you may want to hang a second door that opens the other way in the frame. If none of this is practical, a really heavy curtain over the door will help some.

External windows are a real problem, since a single layer of ordinary glass is only slightly better sound insulation than nothing at all. Storm windows are a big help, especially if you fill the space between panes with fiberglas. (You don't really need to see outside, do you?) Thermal glass is actually worse than a single pane window because the narrow air space tends to resonate. Seal the movable part of the window with good gaskets, then cover the whole opening with heavy drapes. Make sure the drapes fit snugly against the wall all the way around. An inexpensive alternative to drapes is a solid piece of 3/4" plywood, gasketed just like a door. This can be hinged to the wall as shutters or in a sliding track, just as long as it fits tightly.

Electrical fittings are another source of leakage. Take the plates off light switches and receptacles, fill the gaps between the box and the gypboard, and add a sealing gasket when you put the plate back on. If switches or receptacles are found back to back in both sides of the wall, the gasket will not be enough to stop sound. Replace the electrical box with a surface mount type, and patch over the original hole. If you aren't up for rewiring, cover the offending outlets with a weatherproof hinged cover.

Air ducts present a special problem. You don't want to cover them up (even keyboard players have to breathe), but they are a veritable freeway for sound. To soundproof air vents build a baffle as illustrated in figure 4. Start with a rectangule of 3/8 in plywood as large as you can fit into the space. Cut a series of slots for the air to pass through, and cover the back with fiberglas, leaving the slots clear. Hang this at an angle in front of the duct and fit triangular pieces over the ends.

Fig. 4 vent baffles

Put one of these on each vent connected to the studio ducts, even those in other rooms. If this isn't enough, you can add a second unit in front of the first.

Step 3: Beef It Up

As I mentioned earlier, low frequency sound can actually resonate a gypsum board wall just as it will rattle a drum head. When this happens, the bass might seem louder in the next room than it is in the studio! The only cure short of tearing the wall down and rebuilding is to add weight, usually another layer of gypboard. This is most effective if the new gypboard is thicker than the original and if it is glued in place rather than nailed to the studs.

There is no point in doing this halfway-- you must cover all internal walls, preferably on both sides. Additional gypsum gives diminishing returns, but an intermediate layer of soft fiber board can be helpful.

Even if there is no direct air route for sound to follow, there can be flanking paths around heavy walls through thin ceilings or floors. The sound will then pass through the attic or crawl space into adjoining areas.

You can add gypboard to a ceiling either directly on top of the existing material or suspended a few inches below. In some cases it would be simpler to extend the side walls all the way up to the roof. A properly built hardwood floor should not leak much sound, but sometimes contractors cut corners when a house has wall to wall carpet-- you should lift a corner of the carpet and see what is really below.

The Ultimate Solution: Double Up

Truly isolated spaces are created by building a separate room within the room. Both the external room and the internal room have to be tight and heavy and there must be no solid connection between the two, not even the floor. You can buy prefrabricated isolation rooms (at a hefty cost), or you can build one using construction techniques similar to that of the house. Something like this should really be designed by an architect to fit your situation, but here is a typical plan to give you the idea.

Fig 5 Plans for a room within a room.

The inner room is built on a platform of 2X4s covered with two layers of 3/4 inch plywood. The platform is supported by neoprene pads that line up with the floor joists. There must be no other connection between the room and the house. The walls and ceiling are built on the platform using 2X4 studs and double gypboard on the inside only. The space between the walls should be at least one inch (wider if practical) and lined with fiberglas. The air duct should be very long and lined with sound absorptant material. Get the heaviest solid door and frame you can find, and add gaskets as described above.

These steps can result in a very quiet space, but they get progressively more expensive-- the real question is when is it quiet enough? The easy test is to make a recording of the space. No sound, just a tape of the mic levels at their usual setting with nothing going on. Now turn up the gain and play it back. If you can't hear any difference between the unrecorded and recorded portions of the tape you have reached your goal.

The only way to get an objective measurement of sound levels is to use an SPL meter. (There are some inexpensive models by Gold Line/loft or Radio Shack.) As measured by the "C" scale on these meters you will find the following numbers appropriate for these uses.

• Good resturant 35-45
• Quiet office 30-40
• Hospital room 25-35
• Church 20-30
• Concert hall 15-25
• Recording studio 10-20

A decent home studio should measure in the 20s. Assuming all noise sources are outside the room, you can calculate the amount of transmission loss the walls have to provide by measuring the sound level with the door open. Close the door and you can figure what you already have. If the level does not change when you close the door, you know where to start!

Part 2: Room Treatment

Has this ever happened to you? You are playing your latest masterpiece at a party at a friend's place, and when the best song comes on you want to hide under the couch-- the bass is boomy, the highs screech, and along with the backup vocals you can definitely hear Gilligan's Island. If you find this experience familiar, you are probably the victim of BAD ACOUSTICS.

You won't be surprised to hear that the shape and furnishings of a room can affect the way things sound-- we have all experienced extreme cases such as large echoey bathrooms and overstuffed restaurants. These effects can easily happen in a subtle way in your studio, causing inaccuracies in the sound from the monitors. When you record or mix you adjust the music till it is right in your control room, but when you play the tape in a neutral environment the sound is overcompensated and strange.

There are expensive instruments available to measure the quality of sound in a space, but the best ones are on the sides of your head. You can compare rooms by listening to familiar recordings. (It doesn't have to be on CD-- you can tell a lot from the quality of hiss on a tape.) In a good room, the bass is balanced and clear, cymbals "shine" without being harsh, you can understand words without effort. A mono signal appears to come from a spot exactly between the speakers, and that spot does not jump around with changes of pitch. Now listen to the quiet-- can you hear a refrigerator, a TV, traffic on the street? Clap your hands--you should hear a slight broadening of the sound, but little reverberation and certainly no pitches or echoes.

These simple tests should tell you about any severe problems the room may have. Subtle ones will show up in the music produced in the room, as described above. You may be surprised to find that the control of the sound of a room is not really very complicated and can usually be accomplished with inexpensive materials.

Some More Theory

The goal is very simple-- we want to get the sound from the speakers to your ears without messing it up. This is really just a matter of what becomes of the sound after it passes your ears.

There are three things that can happen when sound hits a wall. It can be reflected, absorbed, or diffused. If the wall is flat and hard, the sound will be reflected. A single strong reflection can sometimes be heard as an echo, but in most rooms a lot of reflections (including reflections of reflections) combine into the reverberation. The aspect of reverberation you hear about the most is reverberation time. This is the amount of time it takes a loud short sound to die away. "Dying away" can be defined more scientifically as a drop in loudness of 60 dB, so acousticians call reverberation time RT60.

The amount of reverberation desired in a room depends on the activity going on. Musicians like fairly long reverberation times; between one and two seconds. This allows them to hear themselves play and enhances the harmonic effects of the music. (In larger rooms even more reverb is desirable because it helps fill the hall with sound.) For listening to speech or music played through loudspeakers this amount of reverb is too much-- values around a second are more comfortable, and for critical listening to speakers the RT60 should be close to a half second.

Reverberation time is determined by the volume of the room. It can be reduced by replacing some of the hard, reflective parts of the the walls with soft, absorptive sections. Every material has some absorptive qualities. This is described by its coefficient of absorption, a number between 0 and 1, with 0 being totally reflective and 1 being an open window. For instance the COE of brick is 0.04, whereas that for heavy drapes is around 0.6. The effective absorption of a surface is simply the COE times the area of the surface in square feet. These numbers can be used to compare materials and to predict the results of treatment. The absorption ability of most materials is frequency dependent, which can cause problems as described later.

Reflections off flat walls can sometimes combine to produce undesirable effects. The worst of these is the standing wave.

Standing Waves

Standing waves are created when you have two parallel facing walls. There will be a particular set of frequencies that are reinforced by the distance between the walls (the sound makes exactly one round trip on each cycle of the speaker and the pressure fronts pile up). This is what happens in bathrooms- you probably know one where the deep tones of your voice are tremendously supported (doesn't everybody sing in the shower?). Most rooms have three pairs of parallel surfaces, and the dimensions are usually just right to affect music. An eight foot ceiling, for instance, reinforces 70 hz. ( This is called a room mode.)

This phenomenon can be prevented by designing the room with nonparallel walls. It can be cured in existing rooms by making one of the walls absorptive or by breaking up the flat surfaces. When sound is reflected off a rounded or complex surface, it is diffused. Diffusion spreads the reverberant sound evenly throughout a room, which not only prevents standing waves but also eliminates "dead spots"-- places where components of the sound are missing.

We can break up flat surfaces by hanging large objects called diffusers. The shapes chosen for diffusers are really a matter of taste and cost. Avoid concave curves, which focus sound instead of dispersing it, but otherwise pyramids, lattices, or computer designed random surfaces all work well. The depth of a diffuser determines the lowest frequency that will be affected. A diffuser one foot deep will scatter sound down to 160 hz.

Fig 6. Some popular shapes for diffusers.

Reflections can cause a further problem when the principal activity in a room is listening to loudspeakers.

Interference

You may be familiar with phase interference from recording work with multiple microphones. If a sound arrives at a single point via two paths at slightly different times, certain frequencies will be reinforced and others will be weakened. You can easily hear this by putting your ear close to a wall: the quality of sound will change because the reflections off the wall interfere with the direct sound. The effect is at its worst when the distance the reflected sound travels is only slightly longer than the direct distance.

Phase interference is attacked by careful consideration of the placement of speakers and the listener. In general avoid locating either so that there are short reflective paths off of walls, ceiling, or equipment. The worst problems occur when a speaker winds up in a corner. If this is unavoidable, figure out where the reflections occur, and make that part of the wall or ceiling absorptive.

Coloration

What I've said so far might seem to imply you can take care of all acoustic problems by making every surface absorptive, completely deadening the room. Actually, such a room is rather unpleasant to work in, but even if it weren't, any attempt to create it would probably be a disaster. The problem is that all absorptive materials are frequency selective. As a general rule, high frequency sound is absorbed more readily than low, so as absorption is added to a room, the reverberation becomes more and more bassy in tone. Some of this coloration is ok, even preferable, but eventually the room develops a tubby response. If we need a very dead room and bass buildup occurs there are devices called bass traps and Helmholtz resonators that absorb a restricted range of very low frequencies. The specifics for designing these are beyond the scope of this article, but the general principle is the larger they are, the lower the frequency. The moral is that absorption should be used only in moderation, and only materials that soak up the full range of sound should be used.

Such materials need not be expensive. In fact, ordinary R-19 fiberglass insulation (about 6 inches thick ) is as good a general purpose absorber as you can find and costs about 30 cents a square foot. You can tack it right to the wall, paper side down. Of course this is ugly as sin and breathing fiberglass is not good for you, so you want to cover it up with some lightweight cloth. More attractive absorbers can be made from Insul-shield (a solid wall insulation material) or various foam products sold through audio supply houses. (Again see sidebar) These all work down to 100 hz or so. Carpet on a thick pad is a decent absorber down to about 250hz. It is the simplest way to control floor to ceiling standing waves, and if hung in deep pleats works well as a wall treatment also.

We can get away with materials that poop out below 100 hz because normal wall and floor construction is absorptive in the low end but very reflective above 200 hz. This means that the reverb in an empty room is almost always bass shy.

These facts suggest a fairly simple recipe for tuning a room: Add absorption until you reach the point where the new material balances the original curve of the room, yielding a reverberation with a nice flat frequency response. Place the first panels near the speakers where they will eliminate interference paths, then spread the rest through the room to cut out any standing waves. If you are left with parallel hard surfaces, put diffusers on them. This method does not allow direct control of the reverberation time, but for any room smaller than 2000 cubic feet the RT60 should fall into the usable range.

A Sample Design

As an example of how to apply these principles, let us look at an ordinary room in a typical house. (All right, it's my wife's studio in my house!) This room is rectangular, about 11' by 13' with an eight foot ceiling. There is a large closet at the back of the room and a window at the front looking onto a suburban street. The closet helps isolation because it provides something of a double wall between the studio and the living room.

Fig. 7 A treated room.

There was a plush carpet over a thick pad on the floor, but no other absorptive material in the room to start with. The clap test in the empty room suggested a moderately long, primarily high frequency reverberation and produced the characteristic "chirp" of a severe standing wave problem.

Some Isolation

After adding gaskets to the doors, isolation from the rest of the house is adequate as long as recording is limited to quiet times. (We checked this out before we moved in!) Noise from the street is an occasional problem which was helped a little by drapes on the window. An additional drape across the doorway made only a slight improvement in isolation and was really in the way, so we gave it up.

Positioning the Equipment

After some experimentation, we decided to locate the speakers each side of the window. Since speakers tend to move gypsum as well as air, outside walls are always your first choice if you are concerned with sound control. Incidentally, these are obviously not near field speakers. Near field monitors should not be against a wall, but most large systems depend on a wall backing for extended bass response. The speakers were hung about 6 ft from the floor. This is a bit on the high side, but was necessary to allow the placement of a writing table underneath them.

The speakers wound up eight feet apart. This placed the "sweet spot" eight feet from the wall along the center line of the room. This in turn dictated the location of the mixing board and other equipment. Once the equipment was set in place, we checked for reflective phase interference from the console or cabinet tops. This can be tested with a mirror and a flashlight. Set the mirror on the console and hold the flashlight by your ear aimed at the mirror. If the light beam falls on or near the speakers there is a potential reflection problem. This can usually be fixed by propping up the back of the board.

Wall Treatment

At this point we were down to two problems: the rising frequency response of the reverberation and the standing wave. We attacked both problems at the same time with some carefully placed absorptive panels. These were made of R-19 fiberglass and measured 2 ft by 6 ft. (They do not need to extend down to the floor because the furniture scatters sound at that level.) Most of this absorption wound up on the walls near the speakers-- this cleaned up the last of the short delay reflections and resulted in a very clear sound image between the speakers. The absorption was brought along the side walls to soak up the standing wave. We wanted to keep the room symmetrical, so we spaced out the absorptive panels, winding up with a pattern where bare wall on one side was opposed by absorption on the other. A large section of absorptive wall near the left speaker created a dead corner for recording vocals.

The curtain over the window Is too light to be a really broadband absorber, but it combines with the low frequency absorption of the glass to give a reasonably flat overall effect. The carpet and wooden floor interact in much the same way.

We found the sound to be balanced in frequency when the walls were about one third covered with fiberglass. This left the side walls near the back of the room untreated so we added diffusion. This is provided by some homemade diffuser panels on one side and some very cluttered bookshelves on the other.

*s

The Numbers (and Initials) of Acoustics

Architectural acoustics is about half engineering, half art. The art comes from experience in choosing, placing and evaluating various materials and structures. The engineering comes from measuring the effects of the materials and structures and relating what can be measured to what can be heard. There are standards for making test measurements so you can compare specifications from various manufacturers when choosing materials and prebuilt items such as doors. The standards are also used in specifying and evaluating performance of finished construction such as floor, wall, and window isolation.

Graphs

Many acoustical numbers are presented as curves on graphs. In order to accommodate the nature of hearing, peculiar graph paper is often used. The horizontal divisions represent frequency, but they are spaced in such a way that an octave is the same width anywhere across the graph. Notice that each mark up to 100 represents 10 hz, each from 100 to 1000 represents 100hz, and from 1000 to 10,000, each is 1000 hz. The spacing is therefore logarithmic. The vertical divisions are equally spaced, but since they are marked in decibels, the graph is logarithmic in this direction also. This makes the perceived effect of any deviations in the curves the same anywhere on the graph.

Fig 1 Logarithmic graph paper

Equal Loudness Curves

You will see lots of references to equal loudness curves or equal loudness contours- these are based on the work of Fletcher and Munson at Bell labs in the 30s, or perhaps refinements made more recently by Robinson and Dadson. These were made by asking people to judge when pure tones of two different frequencies were the same loudness. This is a very difficult judgement to make, and the curves are the average results from many subjects, so they should be considered general indicators rather than a prescription as to what a single individual might hear.

Fig 2. Equal loudness contours or Fletcher-Munson curves

The numbers on each curve identify it in terms of phons, a unit of loudness that compensates for frequency effects. To find the phon value of an intensity measurement, find the db reading and frequency on the graph, then see which curve it lands on.

The interesting aspects of these curves are that it is difficult to hear low frequency of soft sounds, and that the ear is extra sensitive between 1 and 6 kilohertz.

SPL

Sound Pressure Level is a single measurement of sound pressure in decibels relative to the threshold of hearing. That varies from person to person of course, but for the purposes of SPL measurements is defined as 2 X 10^-5 Newtons per Meter² or 20 microPascals. We generally live in the mid 60s db_SPL, think music is loud when it gets above 90 db_SPL, and complain of pain at 120 db_SPL .

When SPL measurements are made, some adjustment for the ear's response to low frequency is usually included. This is done by using filters that follow the Fletcher-Munson curves - the A curve follows F&M at low levels and the B curve follows intermediate levels. The C curve is nearly flat.

FIG.3 SPL Weighting curves,

If it seems odd that these curves turn down when the equal loudness curves turn up, remember that this is a frequency response and the loudness curve indicates sensitivity. The idea is that if you find noise at a low level and low frequency, it doesn't count for much since it is hard to hear.

SPL is usually measured with special meters that have the weighting curves built in. Use the A curve for soft measurements and the C curve for loud sounds, and the flat setting for comparative measurements like transmission loss.

NC

Noise Criteria levels or NC ratings are a common way of specifying the background noise in rooms. It's not quite the same as SPL- there is a special filter used which discounts low frequency sound even more. It also only includes about half of the audible spectrum. Generally, A weighted SPL readings run about 10db higher than NC readings.

Fig. 4 Noise Criteria curves

To get an NC value, find the curve that is just below all of your measurements. You can see from these curves that an environment that measures NC-20 could have a 50 db level of 60hz hum. Although the Fletcher-Munson effect would make this tolerable for a classroom, it's not appropriate for a recording studio, because soft sounds are often amplified to the point where our hearing response is flat.

TL

Transmission Loss is simply the reduction of SPL as sound travels through a structure. It will vary with frequency, and should be presented as a curve or series of numbers at selected frequencies. Very often you see a chart like this:

Fig 5. Transmission loss

This gives the transmission loss in db at the frequencies listed. Notice the last entry, instead of a frequency, is an overall rating called STC.

STC

Sound Transmission Class is another set of curves, again relaxed in stringency at low frequency. To convert a TL curve to STC, you find an STC curve that fits the measured curve within 8 db, then specify the value from the STC curve at 500hz. This is useful for comparing products in a catalog, but the true transmission loss curve is necessary to predict what will happen with music.

Absorption Coefficient

The absorptive efficiency of a material is given by its Absorption Coefficient, which is the ratio of the sound energy that is reflected back to the arriving sound energy. A totally reflective material has an absorption coefficient of 0, and an open window has an AC of 1. As with most things acoustical, the value varies with frequency, although you will often see a single number specified. Here's how various thicknesses of Fiberglas stack up:

Figure 6. Absorption Coefficient of Fiberglas.

NRC

The Noise Reduction Coefficient of a material is the average absorption measured at 250, 500, 1000, and 2000 hz. It's useful for designing offices, but not sound studios. Even the complete specs given above don't tell what happens in the lowest octaves, although you can guess from the trend of the curves.

Speed of Sound

The most important number to remember is that the speed of sound under typical conditions is 1130 ft/second. This varies with temperature (slows down when it's cold) but not with any other conditions you will encounter in recording studios. For many purposes, we can use the rule of thumb that sound travels a little faster than one foot in a millisecond.

Frequency

This how often something happens. For a steady tone, the frequency is the number of wavefronts that pass your ear in one second. It is measured in hertz or hz, which can be though of as meaning 1/sec or "per second". We usually consider the audible range of frequency to be from 20hz, to 20,000hz. Few people can hear all of this range, but some can hear beyond.

Wavelength

This is the distance between wavefronts of a steady tone. It is often represented in formulas by the greek letter lambda, which looks like an upside down y.

The formula.

Remember the relationship between frequency, wavelength and speed of sound is:

Wavelength = Speed_of_Sound / Frequency

 ources 

http://www.ucsc.edu

http://www.ItchyTastyRecords.com

http://artsites.ucsc.edu/EMS/Music/

Happy Holidays From Itchy Tasty Records

Itchy Tasty Records Mascot Yuck Fou

Itchy Tasty Records Mascot Yuck Fou

Itchin to hear some tasty beats?
-Itchy Tasty Records
http://www.ItchyTastyRecords.com

The classic Amen Break and its influence on modern electronic music.

The classic Amen Break and its influence on modern electronic music. 

The Amen break is a 6 second (4 bar) drum solo performed in 1969 by Gregory Cylvester "G. C." Coleman in the song "Amen, Brother" performed by the 1960s funk and soul outfit The Winstons. The full song is an up-tempo instrumental rendition of Jester Hairston's "Amen," which he wrote for the Sidney Poitier film Lilies of the Field (1963) and which was subsequently popularized by The Impressions in 1964. The Winstons' version was released as a B-side of the 45 RPM 7-inch vinyl single "Color Him Father" in 1969 on Metromedia (MMS-117), and is currently available on several compilations and on a 12-inch vinyl re-release together with other songs by The Winstons.

It gained fame from the 1980s onwards when four bars (6 seconds) sampled from the drum-solo (or imitations thereof) became very widely used as sampled drum loops in breakbeat, hip hop, breakbeat hardcore, hardcore techno andbreakcore, jungle and drum and bass (including oldschool jungle and ragga jungle), and digital hardcore music. The Amen Break was used extensively in early hiphop and sample-based music, and became the basis for drum-and-bass and jungle music—"a six-second clip that spawned several entire subcultures." It is arguably the most sampled drum beat of all time and unarguably one of the most sampled loops in contemporary electronic music.

 amen break waveform

In Modern Music - 

By 1990, at the height of British rave culture, the Amen break began to appear in an increasing number of breakbeat hardcore productions. Hardcore emphasized a unique, harsh, aggressive sound that drew strongly from hip-hop and early acid house. It added a hip-hop influence with the addition of breakbeats and increased the tempo. A strong reggae and ragga influence emerged in 1991 and 1992, with uplifting piano melody loops or Jamaican reggae samples used at normal speed layered on top of frenetic 150 to 170 BPM breakbeats. This sound quickly evolved to a point where sliced and diced drum breaks in conjunction with low frequency bass lines became the important features of many tracks. This style was initially referred to as Jungle but later, as it progressed and rhythmic elements were refined, the term drum and bass became more common. Around the mid-1990s a number of IDM producers, who had been influenced by the Jungle/DnB sound, began to focus on the style and started exploring it in the context of electronica. Making "danceable" club oriented tracks was not a prerequisite. In fact, the more outlandish and obscure the manipulations, the more aesthetically pleasing the records were to aficionados—a trend that continues to this day in the form of breakcore. The Amen break can still be found in many productions and there has been a renewed interest in the "old-skool" Jungle style in recent years. Luke Vibert, one of the many IDM producers who has explored this break, has released several records under the moniker Amen Andrews, using the Amen on nearly every track, heavily sliced and edited, yet recognizable.

It is also used by some cross-genre artists such as DJ Axera and Gomanda and in many hip-hop tunes, such as N.W.A's Straight Outta Compton.[5] The first Hip-Hop producer to dismember the drum sounds of the Amen break and reprogram them into a new pattern was Mr. Mixx of 2 Live Crew on their 1987 song "Feel Alright Y'all" from the Move Somethin' album, followed by the Mantronix sample-heavy track "King of the Beats" in 1988. The Amen break has also been used by rock music acts including Oasis ('D'You Know What I Mean'), Nine Inch Nails ("The Perfect Drug"), Rammstein ("Sehnsucht") . It can even be heard in the background of car commercials and television shows such as The Amazing Race, and Futurama. One other recent example can be found on rapper Lupe Fiasco's 2007 album, Lupe Fiasco's The Cool in a song titled "Streets On Fire".

*sources*

http://www.bbc.co.uk/programmes/b011nyd1

http://www.youtube.com/watch?v=5SaFTm2bcac

http://www.itchytastyrecords.com

http://www.youtube.com/watch?feature=player_detailpage&v=5SaFTm2bcac#t=699s

Soundproofing 101 with Itchy Tasty Records Acoustic treatment - 101- for sound isolation, Acoustic tuning, Acoustic education and best sound acoustic methodology for apartments, studios, dorms and homes

Soundproofing 101 with Itchy Tasty Records Acoustic treatment, sound isolation, Acoustic tuning, Acoustic education and best sound acoustic methodology for apartments, studios, dorms and homes.

I have been doing this for a long time now and after thousands of hours of labor and research the following is the best and most cost effective methods i have come up with for the best sound isolation, blocking and room acoustics. 

Lesson One Will Talk about

1 Why are room acoustics important and Why we need acoustic treatment

2 .What needs to be treated. 

3. Box in a Box Theory

1 Why are room acoustics important Why do i need soundproofing to be a music producer? 

Music producers have a job that requires us to create, mix, and master tracks that sound good on every type of system. 

In order to do this we need the sounds that come out of the speakers to be freshest of fresh sounds from the tracks (ie sounds heard as they are played in the mix)  

If the sounds stick around in the room or listening space to long, these reverberation cause interactions and coupling of sounds with the newest fresh sounds that are coming out of the speakers. This will  interrupt and impact our ears  in a way that will make us mix and master like a piece of shit producer. 

Coupling occurs in an untreated room. Meshing your sounds into one inaccurate ball of lies.

Coupling is a problem in music production. it means “make as one” - ie in speakers and soundland this means -  2 speakers interfering with another meshing the sound of both speakers into one jumbled inaccurate sound.

If your room, desk, floor, ceiling has to much vibration, coupling occurs and you speakers will give you shit feedback.   

We want to de-couple the sound – where there is absolutely no relationship. float the left loudspeaker  isnt shaking from the impact of the right loudspeaker. Tshus isolation occurs and a more accurate sound can be heard. 

So as producers we need to hear in a flat as possible manner. Flat as in most basic true sound without color from a room, interface, or speakers in order to and accurately judge, create, design, mix or master the task at hand.  

Good room acoustics make the listeners position as accurate and flat as possible. The freshest sounds are heard and gone before the next waveforms interupt the mix.  

Without proper acoustics, you will produce shit mixes and sounds no matter matter what speakers, interface, power, daw, or golden ears you have. 


same reason they make open canned headphones like sennheiser 650 hd for mixing in.  no headphone on the market today is a great enough substitute for a pair of studio monitors and a great room. These elements are essential for every producer. Headphones are like a second reference to check the mix,  just as an avatone is used for. 


2 .What needs to be treated. 

windows
doors
Vents
outlet
walls 
ceilings
floors  
power

For windows, doors, vents, outlets, treatment isolation and sound blocking is quite simple.

For the walls, ceilings and floors sound gets harder to treat so i have designed a 3 layer system that will give you the best acoustic results .

3. Box In a Box Theory

An idea construction for soundproofing is a box in a box theory - everything is floating for best isolation. Also i must add speakers, interface, screen, desk, power, is also floating for best results. ill get into that later. 

If you building your studio from scratch ie building a house or studio on a blank piece of land Mason Uk has the best products and methods around for this Mason Uk Official recording studio methods

Again this is the solution if you walls, floors and ceiling are all ready built. not a guide for fresh contruction sound isolation. If your building the whole place from scratch there is a lot more you can do than this which is much better for clean power, clean sound, acoustics, sound isolation and absorption, but still cost a bundle. However most of us are in a place in which the walls have all ready been put up. So this guide will most likely help you a lot. 


These Few Itchy Tasty Records Acoustics 100 Courses are  the cheapest and most efficient ways to treat your studio. How to treat, isolate, sound proof and create a great listening space/environment for when the walls, ceilings, and floors are all ready built when you get the place!!1 

Stay Tuned for Itchy Tasty Records 102 - 
How to treat - Windows, Doors, outlets, cracks and where the sound leaks.

*sources

http://www.ItchyTastyRecords.com

Dynamite Jacksin - Tunnel Vision - Charted on Beatport's official 10 Must Hear

#electronicdancemusic, #electronicmusiccharts, #musicartists, #topmusic, #electronicmusicnightclubs, #electronicmusicarticles, #electronicmusicblogspot, #topelectronic, #electronicmusician, #new2013, #best2013, #electronica, #EDM, #dancemusic, #undergroundraves, #electronicmusicgenre, #housemusic, #clubmusic, #electronicmusicartistserver, #electronicclassicalmusic, #electronicmusic, #recordlabel, #label, #electroniclabel, #dancerecord, #bassmusic , #techno, #electronic, #afterhours, #losanglesmusic, #losangles, #club, #music, #musicblog, #musicblog2013 #top10 #bestnewtrack #awesome #bestnewartist #bestnewmusic #bestnewelectronicartist  #ItchyTastyRecords #2014 #felix #dj #dynamitejacksin #HuxleysNightmare #king #felixrex #kingfelix #wh1chhouse #balkstar #iviiiix #RME #djm #dynaaudio #losangeles #undergroundmusic

source*
Itchy Tasty Records Youtube
Itchy Tasty Records official

Felix Rex Beatport Premiere - Can You Hear Me?

http://www.beatport.com/track/can-you-hear-me-original-mix/4908658

http://www.beatport.com/release/can-you-hear-me/1195637


An Evolution of Felix has begun. King Felix has Undergone a Binary Fission and split Into two artists/Styles: King Felix & Felix Rex. Felix Rex will take over for the Up-tempo Dance Music Styles. Where as King Felix will Focus on the Down-Tempo Glitch Hop side of Felix. Get Ready For Felix Rex's, Monstrous Bass, Dark Intricate Leads, and Hard Hitting Drums With Felix Rex's World Debut Single, "Can You Hear Me".