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An Introduction to Recording Studio Design
In this article we'll take a (very) quick look at some of the factors that are involved in the design of a space specifically for recording speech, music, or other noises - that is, the basics of Sound Recording Studio design. This involves two different aspects of sound, which can be roughly characterised as 'soundproofing' and 'acoustics', and a host of other technical, practical and commercial factors.
Why should you care about this? Well, the basics here apply to any and all situations where sound is to be recorded. Even if you have no intention of building a studio for music recording, you might want to record a voice on a PC for a presentation. All the same factors will apply, sound-wise, as in a full studio. The same acoustic factors will also apply in your living room or wherever else you listen to music - if you do. So why not read up on how it all works? A little knowledge may be a dangerous thing, but it's a lot better than none at all, in my view!
We'll examine many different facets of the process, because in the sound recording business the technical considerations have rather a special relationship with the rest of the design process; they are crucial -- but secondary. What I mean by this is that the performance of the studio must be entirely adequate for the intended function, but this often comes a long way down the list of priorities!
Because I know British (or at any rate European) practice best, that's what I'll be talking about on the whole. However the only real difference elsewhere in the world is the voltages coming out of the power sockets on the wall, so as long as you allow for the variations in voltages, wiring, and safety requirements, the rest will be much the same. Certainly the acoustics will! I'll also talk about high-end practice as the exemplar, because low-end practice is to do as much of the same as is possible, desirable or affordable!
Before we can talk about the design process, it might be useful (especially
for those of you who don't know anything about this) to have a more exact idea
of what I mean by a 'Recording Studio'. What
a Recording Studio? Here's a ponderous definition:
A recording studio is an assemblage of equipment, spaces and persons such that a performance in sound may be created and recorded onto a medium for later reproduction.
A recording studio is where most music is recorded.
Multitrack recording is still the predominant method of musical assembly work,
though 'sampling' (which we'll get to very soon) is a close runner up in some
ways. For those who are not familiar with 'multitrack recording', the
general idea is to have a sound recorder with many separate audio channels or
'tracks'. When it's a tape recorder that's being used, 24 is still the minimum
professional standard, and up to 32 tracks is commonplace. More can be made
available by slaving two (or more) machines together to give up to 62 tracks
per two audio machines (one track on each analog machine is commonly used for
synchronization code, usually SMPTE code [NOTE 1] . It's commonplace now to record to a computer hard disk, and because of
the tape heritage, the same standards of 24, 32 and other multiples of 8 are
commonplace (but arbitrary). When computer-style or other digital recorders are
slaved together, it's often not necessary to lose an audio track on each.
Each recording 'track' is used for a single musical part, or often in pairs for a stereo part - having 'strings' (usually a violin and viola section at least) or hand percussion on two tracks for stereo, say. Alternatively, a track (or more) can be used for an assemblage or 'mix' of other parts. This can be achieved either by recording the musicians section by section, or by 'reduction' or 'bouncing'. This means the mixing of several previously recorded tracks onto one or more other tracks.
When the recording is finished, the whole lot is eventually mixed down to a final stereo output via the 'mixer', which will have a minimum of one control channel (that is, volume control and tone controls - and much more!) for each audio track. A typical large studio mixer may be able to handle 128 tracks at once, so it will have a minimum of 128 sets of controls for the 128 audio tracks potentially in use, as well as lots of other bits and pieces to hold the whole operation together, and usually a computer to make many of the knobs wiggle up and down all by themselves. A first encounter with one of these large desks can either scar one mentally for life - or cause lifelong addiction! Have a look at this (compact) example!
This sort of multitrack recording process does not and cannot produce true 'stereo' [NOTE 2] . Original Blumlein-derived stereo recording is comparable to the
process of making a hologram, where a sample is made of the whole sound at that
position, the resulting soundfield being reproducible to a surprising degree by
two speakers. Ambisonics [NOTE 3] (as
against quadrophony [NOTE 4] ) continues this principle to add most of the characteristics of the original
space (Figure 3).
Multitrack stereo does not contain the phase differences [NOTE 5] preserved from the original performance that enable true stereo to be produced. All that can be done is to adjust volume levels between the channels, and so utilising the Haas effect [NOTE 6] to give an impression of the lateral positioning (see Figure 4) , though sporadic attempts have been made to add variable phase delay. The problem is that in general, the audience can't tell the diference *sigh*. So much for Hi-Fi.
This lack of true stereo is not particularly important with popular music, the bulk of which is now sourced from assorted computerized instruments that don't have any acoustic output at all to preserve. This fact does however make a mockery of some of the excesses of the hi-fi brigade with regard to perfectly-reproducing something that didn't ever actually exist. With classical material, the story is different, as true Blumlein techniques are often combined with multiple miking of instrument sections or soloists in order to control and balance each section. This is tricky to implement effectively as the separate feeds for the soloists or sections are arriving with a different time delay to that from the stereo pair of mikes...
Various Sound Studio types exist. The traditional down-market 'demo' studio, which was used for low cost recording of demonstration material, is either very rapidly disappearing or already gone. The cost of low-end professional-quality equipment has dropped, so the output-quality distinctions between studios are less clear-cut nowadays. However, some fairly arbitrary classification into types can be made. The descriptive labels I use (other commentators may well differ) are as follows:
A studio built in someone's home! This is not in any way a pejorative description. A lot of high-performance but economical equipment is available now to enable the creation of release-quality material in home studios. We can make a distinction, based on the general quality of output, thus:
A semi-pro studio will have the facilities to make demonstration material and experiment with production ideas without incurring the high cost of using a professional studio.
A 'pro' home studio is essentially a private professional recording studio, with all the same design criteria applying. Material can be recorded to release standard.
These studios primarily deal with the addition of soundtrack material to the finished edited visuals for movies and commercials. They will often have facilities for recording large-scale orchestral performances whilst simultaneously projecting the film that is being worked on. Equipment will include that necessary for synchronization of audio to film, and processing films for Dolby Stereo or multi-channel formats.
Radio studios have to deal with a broad range of material. Small studios are used for voice material such as interviews and drama; slightly larger ones can also deal with small-scale music recording. Speech and drama studios are optimized in terms of acoustics and equipment for speech recording. There are very few studios of this type outside radio.
Cutting studios specifically deal with transfer of material from tape source to master discs, with appropriate 'final tuning' for best results. In the original (1990) version of this article, I predicted that 'the number in this category will drop as more direct digital material is released on CD', but I was wrong in that prediction. The expertise of the mastering engineers in getting the best possible result in the final processing is just as relevant to making a CD, so now they cut CD pressing masters instead!
There were once two main categories of pre-production studio - MIDI based and
'track-laying' studios, though they now are merging into an indistinguishable
whole. A MIDI (Musical Instrument Digital Interface) studio is primarily
computer based, with usually a software-based sequencer (there's still some
dedicated ones available) controlling various sound sources, keyboards, drum
units and effects units. The advent of low-cost fully digital mixers has
meant that a high level of automation can be applied, though (speaking from
personal experience!) this can take more time to set up than it saves.
The whole lot will be locked to a timing mechanism either recorded on one track
of an analog multi-track recorder or generated by a digital one, which is then
used for synchronized vocals, guitar and other 'real' sound sources that are at
present not equipped with digital I/O!
A track-laying studio concentrates more on providing excellent quality acoustic recording (usually offering only limited mix-down facilities), so that the bulk of recording hours can be done at relatively low cost. The output will normally be taken to another (expensive) studio for final polishing and mix-down.
Sampling-oriented studios are now commonplace, in fact almost all
chart-oriented work includes some sampling. What you've got is a MIDI studio,
but instead of the sequencer playing back 'raw' instruments from the MIDI
sources, whole sections of music are played back from a 'sampler', which is
just a digital sound recorder specialized for manipulating short sections (from
tenths of seconds up to a few minutes) of digital recordings. In this way it is
possible to take the 'feel' from a track that you like and thus not have to
learn to play it properly yourself.
You may gather from this remark that I started out not being over-keen on the sampling approach, which proves I suppose that I'm getting to be an old ****. "You lot don't know when you're well off; back in my day, you'd have to live for a week on the price of a cup of coffee now, and a musician was a mus..." yeah all right I'll shut up. A few years ago there was a great deal of fuss about sampling, but it all seems to have settled down now, and the music business seems to continue to make a profit, somehow (poor things). Of course, as is always the case, some artists have taken the sampling technology and come up with something really special that cannot be regarded as derivative of anyone or anything.
In sampling you are sometimes working with complete tracks of (say) bass, drums, percussion, rhythm instruments. For this reason, it's not always necessary to have a huge number of recording tracks on the main recorder (whatever you're using). We could paraphrase a remark here: 'It's never possible to be too rich, too young or have too many recording tracks' (thank you, Mrs. Simpson) but in a sampling environment you can get away with less tracks than in some other circumstances and still produce professional results.
The old type of Mix-down or Remix studio specifically dealt with the reduction
of multi-track material to finished masters, usually stereo. A remix studio
will concentrate more on making new versions from existing multitrack
masters. They will have heavy investment in sound processors and
modifiers, and whole racks of samplers. They'll often have the ability to
synchronize several multi-track recorders to allow new material to be added to
the original but on a separate tape, to maintain the original recording.
All of these studios can be constructed on a small or large scale, depending on the intended market and budget. It is common for a particular studio to be able to cover more than one of these applications, and large complexes may offer all of these facilities in-house.
What's the difference between budget and cost? The budget is the amount you
are willing to pay to get the studio going. The cost is the amount you end up
paying. You'll perhaps not be surprised to hear that the two rarely coincide,
and I bet you can guess which one usually is the larger.
If you seriously want to run a commercial studio, you'll have to be pretty clear on exactly why you want to do something so fundamentally perverse. There have to be sound commercial reasons for setting up a studio in this very competitive marketplace. It used to be that publicly financed bodies like the BBC did not have to consider the market, as most material related to internal consumption, but at a professional level it's all got so expensive that they too have to be cost-oriented nowadays.
If you do intend to build a studio, then the usual aspects of market research need to be taken into account. These are typically - what do the customers want, what do they like that is already available, what don't they like, how far are they prepared to travel, how much are they prepared to pay, what special features can be offered that will be exclusive to this studio, and so on.
Location is an important issue. The preferred location will depend, in the first instance, on the intended market for the studio. For example, many studios are located for easy access by local clients - local meaning, for example, the same city. Some studios are located in the country for a quieter working ambience, or higher pretentiousness factor. Such a studio would normally be residential.
Size is yet another strategic decision. If you want to record 100-piece
orchestras, then you'll need a very large studio room. Many larger commercial
facilities have several separate studios within them (rather like a cinema
complex, really!), offering sometimes-overlapping spaces for different types of
work. This is practical, because the recording process often has different
phases with different needs. You frequently can get the band (be it 1 piece, 5
piece or 100 piece) down on tape/disk quickly, and then spend the rest of the
week coaxing something other than sulks and prima-dona-isms out of the soloists
in a much smaller (therapeutic? womb-like?) space, leaving the big studio rooms
free for other acts to use.
Studios normally require twenty-four hour access for arriving and departing clients. In some special circumstances this might not be required. A studio dealing with large-scale recording will have good access for the transport of large-scale equipment - stairs and narrow alleyways are inappropriate. Think 'elevators' (or 'lifts' if you're British).
There are two aspects to this. Various people wanting to build a studio in a
residential neighborhood have discovered that their prospective future
neighbors will be most alarmed at the prospect of having a studio near them,
both because they expect loud music (not usually the case) and the coming and
going of lots of people (which is usually the case).
Secondly, it is generally not a good idea to build a studio under the flight path to Heathrow/LAX/Paris de Gaulle (you get the idea), under a railway siding or next to an elevated motorway, though if funds are unlimited it can indeed be done (but there'd better be a very good reason).
Vehicle parking is another significant issue. You may end up with ten vehicles for each 4-piece band you deal with. Many musicians (or at least their gear) turn up in trucks. Not so very long ago, a large and well funded studio complex in Central London closed down after six months trading, largely because it was situated in Piccadilly and there was nowhere for anyone to park. Silly. Expensive and silly! Learn from their errors.
Studios usually require local planning/zoning permission, and specific permissions may be granted only on various conditions. You'd be well advised to ensure you find out what these may be (in triplicate, notarised if possible!) before handing over any money for the premises. You'll also have to (and I hope, want to) comply with Fire and Sanitary regulations, dependent on the size of the intended studio and the numbers of people usually there. For example, you may need a separate little girl's room and little boy's room instead of a unisex facility.
Choice of recording format has always been something of a problem. Some formats recently used for recording and still available are shown in Table 1:
|Analog formats||Digital formats|
|Stereo on 0.125 inch cassette||Stereo PCM to Betamax|
|Stereo on 0.25 inch tape||Stereo DAT|
|Stereo on 0.5 inch tape||8 track on approx. 8 mm cartridge|
|2 track on 0.25 inch tape||12 track on approx. 0.5 inch|
|3 track on 0.25 inch tape||24 track on 1 inch 32 track on 1 inch|
|4 track on 0.125 inch tape||24 track on 1/2 inch tape (DASH)|
|4 track on 0.25 inch tape||48 track on 1/2 inch tape (DASH)|
|4 track on 0.5 inch tape||8 track ADAT|
|6 track on 0.125 inch cassette||8 track Tascam|
|8 track on 0.125 inch cassette||Optical disks of various types, sizes, capacities and interfaces (mostly SCSI or IDE).|
|8 track on 0.25 inch tape||Hard disk drives of innumerable varieties but only two interfaces, SCSI or IDE.|
|8 track on 0.5 inch tape|
|8 track on 1 inch tape|
|12 track on 0.5 inch cartridge|
|16 track on 0.5 inch tape|
|16 track on 1 inch tape|
|16 track on 2 inch tape|
|24 track on 2 inch tape|
|32 track on 2 inch tape|
Regrettably, the list given above does not exhaust the possibilities. Many of these are 'domestic' formats that would not be used for serious studio work, but you just may have to read the format sometime when someone comes in with something 'important' recorded on it! I've encountered most of these at some point. The analogue formats have variations in
Moreover, the digital formats are all slightly incompatible with regard to the
details of the digital encoding. Small wonder that dealing with tapes
from another studio can at times be somewhat problematic! Fortunately
there are only a few current real standards. The baseline for
professional analog recording is still 24 tracks on 2-inch tape at 15 ips with
NAB equalization, and this format being offered by more studios than any
other. For smaller analog studios, 16 tracks on 1/2-inch tape at 15 ips
with Dolby C has become a subsidiary standard. Stereo analog masters on
quarter inch tape at 15 ips with NAB or IEC equalization were the old stereo
interchange standard, so many studios will be able to make or play these.
Fortunately you can forget about most of the rest of the analog formats (unless
you want to help me remix some odd tapes I've got here :)
The DAT machine failed as a consumer format because of record company paranoia (little did they anticipate MP3!) but it made major inroads in smaller professional studios, where it has taken over from the 1/4 stereo master as a standard interchange format. Overall it offers good results, though many people have unresolved doubts about the long-term stability of material recorded in this format. DAT in a data-style format is also the most commonly used method of backup of digital tracks from a sampler or personal computer. My experience with DAT backup is not good. The main difficulty is poor compatibility with other similar drives, when you want to restore a backup to a different machine.
The bottom-end digital multitrack standard is (currently) ADAT, which offers 8 tracks on a videocassette style medium. Quality is CD-level, but reliability is variable. For more than 8 tracks, sets of cassettes will be produced using multiple synchronized/locked ADAT-format machines, which then have to be played back together to get all the tracks back.
At the top end of the market, when ultimate quality and control are being sought, the decision as to what format to choose is difficult, especially as the price of top quality digital equipment is very high, if not outrageous. (My spellchecker noticed I'd got 'riot' for 'not' in the previous sentence: certainly the price of some equipment almost would warrant a riot!). The market for multitrack digital equipment is, by consumer market standard, minuscule, so the development costs are spread over a very small number of sales. Cost wise, think 'an arm and a leg' plus two mortgages. Moreover, there's a lot of 'fashion' involved in the choice, so all I can say is good luck with it all!
On the other hand, down here on the ground, things have changed a lot for the smaller studio with the introduction of the recent generations of computer equipment. The speed and power of (say) a Pentium 2 or 3 at 700 MHz, plus the ever-expanding size of digital storage media such as hard discs, may well very soon lead to the final demise of tape based storage media, except for long term archive purposes. Even here optical discs show great promise, as the price comes down. I predicted this outcome ten years ago in the original version of this article, and I'm pleased to say I was completely correct! My 'home' recording set-up now can handle better than 32 tracks of simultaneous digital audio with full digital mixing and effects (for example reverberation and EQ), at less than the cost of a single stereo ReVox tape recorder just a few years ago.
Usually commercial considerations will dominate the choice of site.
Thereafter the difficulty is achieving the desired technical specification
within the available budget. Having chosen a suitable location the next
set of problems appear...
Quiet has largely ceased to exist over the last couple of decades;
contributors to environmental noise include jet aircraft, HST, Concorde (if
it's still flying), you name it. Wherever you decide to put a studio there is
likely to be some form of unwanted noise. The site will have to be
surveyed to determine a noise profile. The things you want to know are:
It is advisable to sample over at least a week and all round the clock - in some locations noises only appear at strange times of day, or when the wind is blowing from a particular direction (aircraft noise). Usually the main problems are traffic, trains and planes. The combination of the data regarding noise levels measured and the noise level required inside will give the specification for the sound proofing work.
If building from scratch, the actual work will need to be designed by an architect familiar with studio requirements (and they are few and far between). For example, the practice of putting 'butterflies' or 'ties' between parallel brick walls bridging any cavity is a definite no-no in studio construction, as it destroys acoustic isolation. With an existing building, it will generally be necessary to construct some form of independent structure within the existing walls, and the building's structure will need to be suitable for this, or modified accordingly,
The likely noise sources within the finished studio need to be evaluated and provision made to isolate them acoustically. A condenser microphone can pick up the noise from a 'soil pipe' from quite remarkable distances! In one place I worked this gave an entirely new complexion to the phrase 'flushed with success', which did not in any way speed up the recording process :).
Studio floors have to take a considerable weight. A lot depends, as
usual, on the exact use of the studio, but think 'grand piano, two tons of
musicians, drums, gear and hangers on, plus the multitrack machines (if any),
mixer, large studio monitor speakers...' and on (and on...) to get the
idea. With an existing building, allowance has to be made for sound
treatment being laid on top of the existing floor, as well as the loading to go
on top of that. Often the answer is a new floor, 'floating ' on top of
the existing floor (Figure 5) or independently supported from the walls (Figure 6).
There is a very simple way of reducing noise transmission, and that is to use
'non-resonant mass', lots of it, in the way of the noise source. Really
there isn't any other way to do it, and no innovations on the horizon (to my
knowledge). The problem is that massive construction is heavy, putting
stress on existing structures. It is costly and takes up space, so the
absolute minimum of mass will be used commensurate with the required noise
As long as a wall is non-resonant (it doesn't 'ring'), it will block incident sound to a precise degree, which is known as its Sound Reduction Index - (SRI). This is directly proportional to its mass, and directly proportional to the frequency of the impinging energy. The theoretical SRI will increase by 6 dB (this is sound-speak for 'doubles') at a fixed frequency for the doubling of mass, and for a fixed mass by 6 dB (same) per octave increase in frequency (Figure 7). In this diagram the 'mass law' is shown as the solid line.
The amount of external noise will have been established from the site survey, and the required internal levels will normally be established by reference to Noise Rating (NR) curves (Figure 8). In general, levels between NR 0 and NR 35 will be needed, depending on the application. To give you some idea of what this means, the levels in typical living rooms are also shown for comparison (Figure 9). . To attain and maintain these levels requires some effort (!).
The addition of massive structures is fairly straightforward, but keeping them non-resonant is much harder. Getting light and air to the workspace is important, which also means removing the stale air, usually by ducting. Any gap at all in the massive structure will completely negate the purpose of the exercise, to keep the noise out, so doors must have a very good seal. There are usually two doors in a sound-lock (a bit like an air-lock - normally only one door open at any time), so that noise does not get into the studio area as people enter and leave. There are specialist suppliers of doors, and having tried building custom ones, I would go for the specialist item every time!
Windows are another difficult issue. People (even musicians!) quite naturally prefer to work with daylight. Many studios have given up at this point; just imagine the window construction needed to give the same sound loss as two double brick thickness plastered walls. Well you don't have to imagine it, take a look at (Figure 10) , which is roughly equivalent to a single brick wall and-a-bit in sound loss, so you might need two of them together...
It is usual to provide a 'clean feed' of electricity to power all the control
room equipment, and this supply will often be taken from a different phase from
that used to supply power and lighting for general use within the
building. The studio itself also requires a clean feed and caution must
be exercised here, as it is not unknown for musicians to mix phases when
playing their guitar in the control room with the amp in the studio.
Embarrassing results can transpire (the musicians, of course, can expire - not
good for return bookings). So it is better to keep control room and
studio on the same electrical phase.
The cable runs have to be carefully planned, usually with dirty power and lighting runs placed up high, and clean power down low. Audio cable often is run in the middle of the wall at a convenient height for connection boxes. It gets complex when there are two or three studios all needing separate isolated clean feeds. Standard triac (volume-knob) dimmers are generally doubtful assets in a studio, as they can broadcast radio and line noise if not very carefully suppressed. You can still get variac transformers, though, which make no electrical noise and little heat.
In a studio there are a lot of people handling a lot of mains powered equipment, so RCBs (Residual Current contact Breakers - sometimes called ELCB or ECB) are a necessity. Some countries have them as standard fitting to installations to deal with the vagaries (or vague-aries) of the local electricians. But the standard type has a relatively high break current of 30 mA or so [NOTE 8] . That's not much unless you're a guitarist holding onto it with your two bare (and rather sweaty) hands, so I'd recommend the 10 mA-break types for this job (if you can get hold of them).
Earthing (grounding!) problems can be a nightmare, with ground (earth!) loops
often being set up at the interface of professional and semi - professional
equipment. Double insulation of much musician add-on gear and gizmos (so
there's no ground/earth connection needed) has helped somewhat with this. But
the proper, safe, and certain solution is the isolating transformer (Figure 11).
These are now unfashionable due to the alleged effect on the sound fidelity. I'd point out that most of the best-selling records of all time were made with equipment that was stuffed full of transformers - and many other things to give a hi-fi geek (me?:) the horrors, all of them being then (as now!) the cheapest available parts that would do the job! Personally, I still use transformers. If, however, they are to be avoided, then lots of time will be required to get the system quiet, and much care needed to keep it so. Why not just fit transformers to all inputs that a muso is liable to plug in to, and just lie about it if anyone asks? :)
Studio recording equipment doesn't itself use a great deal of power, but the
associated lighting, heating and air conditioning have to be considered within
a large complex, and so there can overall be a pretty heavy consumption.
This in itself is unlikely to be a problem, but the voltage drop on the main
feeder from the fused supply box when 50 kW of air conditioning cuts in and out
every five minutes or so can be. It may be necessary to arrange
special feeds from the nearest substation transformer, or fit a local
Larger (or subterranean) studios will need at the very least back-up lighting to conform with safety regulations, and almost all large (or country) studios will have a backup generator capable of supplying the full base load of the complex. The necessity of this is obvious; if not, then you can consider the scenario of a studio full of orchestral musicians (say one hundred or so), all quite rightly on Musician's Union rates, waiting for eight hours for power (not!) to be re-established. It's happened... It is just as bad at the lower end having even two people just sitting around waiting for power for the whole day, because you can't really bill them for you doing nothing!
To be continued...
[Note 1] SMPTE stands for 'the Society of Motion Picture and Television Engineers. They're the people who have developed standards to make all the gear work together properly. Well, it does sometimes :)
[Note 2] To enlarge on this: 'Stereo' is short for 'stereophonic' which comes from the Greek root word 'stereo' which means 'solid'. So stereophonic sound is 'solid' sound, placed in space. It was invented by Alan Blumlein. Sorry, you guys with competing claims, it was him, actually. Multi-channel sound was invented by many different people at different times, and goes back to Bell, at least. But 'stereophony' represents the whole of the sound in a space, just as a hologram represents the whole of the space û it's a different idea to multi-channel sound. Blumlein is little known or acknowledged for his many important innovations. This will change one day.
[Note 3] Ambisonics, developed by Michael Gerzon et al, seems to have sunk without a trace - but I bet it'll be back! It's a way of adding another dimension to stereo, which has one plane only available. This usually is set up to be 'front-back and left-right'. Ambisonics adds 'up-down'. If you ever get the chance to hear Ambisonics, try it - you'll be astonished.
[Note 4] Quadrophony has become fairly commonplace as 'Dolby Surround'. It's not quite the same, but you end up with speakers in the corners of the room. You then have to fill in with extra speakers in the front middle because it doesn't work properly otherwise. Ambisonics is much better than this. Honest!.
[Note 5] Phase differences (in this context) are due to the different times it takes for sound to get to the listener from the different sound sources. These are not just the instruments; sound bounces of the walls, floor and ceilings of the room and so arrives from all directions. These sounds interfere with each other and it is this interference pattern that enables the human ear to locate sounds in space. Sometimes we get it wrong, as you may have noticed. Coincident stereo microphone techniques permit these phase interferences to be recorded and accurately reproduced - other techniques usually don't permit this.
[Note 6] The Haas effect (named after Mr. Haas, of course) is this: if the same sound arrives at both your ears at the same time, but one ear gets a much louder version, then your hearing system will be fooled into thinking that the sound is towards that side of the space. This overrides the usual phase sensitivity of the human hearing system, and is the basis of 'stereo' in almost all multitrack popular music.
[Note 7] Equalization originally meant just that, 'making it equal' - meaning tone control, balancing the basses and the trebles. Tape reorders boost the treble on record and cut it on playback to reduce the inevitable hiss level. That's also called 'equalization' and is what is meant here. As has been said elsewhere, 'Standards are obviously a good thing - that's why we have so many of them' :)
[Note 8] 'mA' is the abbreviation for milli-ampere or thousandth of an amp. It's generally reckoned that someone in good health can survive a shock of 100mA for a few tenths of a second. More mA = dead, same as less mA but bad health (heart trouble, for example). 30 mA is (if you are healthy) survivable but painful, 10 mA much less nasty.
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