Recording studio theory

A quick, basic rough and ready guide to recording studio theory by a professional sound studio engineer

Studio microphones are plugged into tie lines in the recording studio. These tie lines run from a wall box in the recording studio to the patchbay in the control room, where by default they are connected to the correspondingly numbered mic inputs on each channel of the desk.

In a similar manner, lines connected directly to the numbered outputs of the multitrack recorder are fed up onto a row of sockets on the patchbay, which are by default connected to the line inputs of the corresponding channels on the desk.

It is possible to bypass either of these connections by plugging a mic or line source directly into the patchbay, but this "normalisation" via the patchbay facilitates a predicable set of default inputs.

This means that during recording, there is a one-to-one mapping between the numbered studio mic input sockets and the channel (mic) inputs, and (during mixdown) a direct mapping between numbered tape tracks and channel (line) inputs, unless re-patched by an engineer.

On the mic inputs there is a phantom power switch. This sends out a 48 volt power supply to drive most expensive condenser microphones. Phantom power gets its name from the fact that the power is actually sent using the audio wires themselves, but without affecting the audio in any way. Having said that, don't turn on the phantom power whilst the mic channel is switched on and turned up!

Also on the mic inputs there is a 20db pad switch. This is to prevent mic amp overload when microphones are placed very close to super-loud sources (such as placing a microphone inside a bass drum), and allows much easier adjustment of the level of such loud sources. The mic inputs and the line inputs pass through separate gain adjustment pots before reaching the main input selector switch on the channel.

Here there is a phase reversal switch, the switch is normally marked on the desk by a small circle with a diagonal line through it. Phase reversal switches are useful for a number of reasons. When you are making a live recording involving lots of microphones, sometimes the sound of one microphone can weaken the sound of another microphone placed further away, because they are cancelling out at an important frequency. Inverting the phase of one or other of the microphones can cure this problem. You get similar problems when mixing the direct sound of an electric guitar with the sound from a microphone on the guitar amp - again, phase reversal of one or other source will cure the problem.

Some mixing desks only have the phase reversal switch on the microphone input (perhaps they implement it by having the switch swap over the two signal pins on the microphone input socket - a technique impossible on unbalanced line inputs). It is a shame not to have phase reversal on line inputs, as it is useful here too. For example, the famous Roland TR808 drum machine, seems to lose impact on its snare drum if a bass drum lands on the same beat. Seeing as this happens slightly with the snare is heard simultaneously with other drums, then the snare seems like a good candidate for phase reversal. Sure enough - flip the phase switch and the snare drum always sounds out loud and strong. Similarly, there are many effects (like flangers,phasers and chorus units), which under some conditions can seem to cancel out the original sound unless the phase of the effected sound is reversed.

Next on the desk we have one half of the "Float" switch. This replaces the mic or line input with a feed from the group output instead. But we haven't covered groups yet, so we'll come back to this later. It isn't an especially important feature or indeed a particularly common one.

Whichever signal is selected, it then passes through an insertion point on the patchbay. This allows an external signal processor to be inserted before the signal then passes into the dynamics and equalisation section of the channel. The dynamics section is a multi-function compressor/limiter/expander/gate with the standard controls such as ratio/threshold/attack/release, athough no output control is provided as the channel itself can compensate for this. Comprehensive switching allows the equaliser to be placed before, after or even inside the dynamics section (for "side-chain" EQ).

After the dynamics and EQ sections, there is another insertion point available on the patchbay, to allow external signal processors to be patched in after any desk dynamics/EQ processing.

The resulting audio (which has not yet been through the channel fader or panpot, is made available to a number of auxilliary sends which can be used across all channels to prepare independent headphone mixes - or indeed any other application where you need a mix of sound that is independent of the position of the main channel fader.

The main channel fader is typically a long-throw type, with a smooth action. Its purpose is to set the output level of the channel (the input level is set by the gain controls for mic/line). During remix, the faders can be seen to reflect the relative audio levels in the mix - but during recording, the faders are typically in a straight line - with just a few pushed a little further up or a little way down, for ultra-fine adjustment of levels during recording.

The exact behaviour of the mute button varies from desk to desk. On some desks it simply cuts the output and is equivilent to pulling the main fader down to silence. On other desks it mutes both the output and the input to the desks - which of course mutes even the pre-fader auxilliary sends. Sometimes when the button has this behaviour, it is called the "Channel on" switch to reflect the fact that it is more that a post-fader mute button.

After the panpot, the signal will be routed to any number of group outputs, and so it is the panpots job to facilitate the stereo positioning of the sound between odd and even numbered groups. When the sound is in the middle, it could sound twice as loud (because it is coming from two loudspeakers instead of one), so the panpot drops the level of the signal when it is in the middle. Some people think it should drop by 3dB, others think it should be 6dB. Some desk manufacturers try to please both schools of thought by having it drop the level by 4.5dB.

There is a panpot on/off switch which bypasses the panpot and hence avoids the confusing drop in signal level when sending sound to a combination of odd and even group outputs, and also avoids the engineer having to keep remembering to pan left when recording on odd-numbered tracks, and pan right when recording on even numbered tracks. It is possible to switch the output from the channel to any number of group outputs. The "routing matrix" also allows the channel to routed directly to the left/right main mix bus.
Making Cost Savings

How much does a desk like the one described above cost? If it's fully automated, then probably around half a million dollars.

Obviously, some major cost savings have to be made in order to make a home studio desk feasible. Let's examine what things we can lose.

Firstly, instead of having seperate "input mixers" and "monitor mixers" built into the frame, the desk can be designed to be "inline". This means that both the input channels and monitor channels share the same channel strip. This allows certain features (such as the dynamics and EQ sections) to be switched into either the monitor path or channel path instead of having seperate ones for both signal paths. This can make a mixing desk much more flexible and is the most common design of mixing desks today.

We can cut also down on the number of group outputs. This offers substantial savings. Remember that groups are really just submixes, and that the number of tracks you need to send a complete mix to for recording is typically quite small - usually, tracks just consist of individual instruments - not a blend.

Even on consoles designed for 48 track recording, the number of groups is limited to half that - just 24 group outputs. This doesn't mean that you are limited to recording 24 tracks at once - it just means that only 24 tracks can independant mixes sent to them - the rest must have direct outputs from channels sent to them instead.

In a project studio, you can get away with substantially less. Even for a twenty-four track setup, eight groups is usually more than enough. You can always connect channels directly to tracks if you need to record more channels simultaneously.

If you believe that the engineer doesn't mind a little repatching, then the "Float" and "Direct" buttons can be removed, as the same facilities can be achieved via the patchbay relatively easilly.

For an eight track setup, four groups or even two is usually enough. Some systems even eliminate groups entirely and use the main stereo mix bus to record from. For off-tape monitoring, you must then listen directly to the "cue" mix. Frankly I think this is taking things a step too far, and substantially limits the practical use of the system. I wouldn't recommend anyone buys a system without group outputs.

Reducing the number of groups is probably the most substantial cost saving a desk manufacturer can make.

What about the "Dynamics" and "EQ" sections? Both are really required for a proper recording session, but dynamics are expensive, and EQ is not. So the EQ is rarely (if ever) eliminated - although it may be "cut down" and less fully-featured than that on more expensive consoles, but the dynamics section is rarely present on desks other than the most expensive models. This eliminates not just the expensive circuitry, but also the complex switching options that having a dynamics section necessitates.

Notwithstanding the above, it is possible to eliminate the EQ section from the monitor channels. Not ideal, but again, even expensive consoles do this sometimes. After all, the material on tape is probably already equalised properly.

A halfway solution is to provide monitor channels with a "cut down" EQ providing perhaps just high and low frequency boost and cut. This satisfies most peoples needs, and when you need more advanced EQ on particular monitor channels, it is sometimes possible to "patch in" an external equaliser or even use a channel equaliser if needs dictate this. Some desks even provide a switch in each channel to allow the channel equaliser to be "removed" from the channel and applied to the tape monitor path instead.

The "panpot on/off" switch is another candidate for elimination. Provided you remember to boost the channel level by a few dB's when assigning to both odd and even groups, then it can be eliminated at the cost of the occasional bit of engineer confusion when a signal appear to not be present at a group output, due to the panpot being panned to the "wrong" side for an odd or even channel.

Can the "Auxilliary Send" pots be removed. Not really. But do you really need that many? Typically you don't need entirely seperate pre and post-fader sends, but a combination of the two. So typically on cheaper consoles there are just two aux sends, with a switch on each channel for whether the sends are pre or post-fader. Additionally, seeing as pre-fader sends aren't used very often, some mixers have only post fader sends.

The "Monitor Channels" have aux sends too. Are these required? My answer is most definately yes! Otherwise how do you add effects to pre-recorded material when you are recording new material? Even so, certain manufacturers of Personal Multitracks have shamelessly removed them, which I think is scandelous. Their "workaround" is to suggest that if you need sends on recorded material then you should switch the relevant channels to "mix" mode and use the channel to send effects. I don't find this acceptable, because it means you must lose your channel settings (which you may have meticullously set up to record seperate instruments), purely to add effects to off-tape material.

A better cost saving solution, which is commonly adopted, is to have two or more aux sends per channel, which are switchable pre or post-fader but also switchable to be either in the channel path or the monitor path. This is a much more desireable solution which even the most expensive consoles adopt.

What about the complex PFL/Solo system? Well, it's certainly useful - but on a small (say) eight channel system, it isn't too much hard work for the engineer to mute the seven unwanted channels to concentrate on one channel in particular.

A similar argument applies to the "Mute" switch. Can't you just pull down the faders? On a large console this would be unthinkable, as you would lose your comples mix fader settings. But on an eight channel (or less) system it isn't particularly hard work to set up a mix (or note the settings on paper). For this reason, simple desks do not usually have the PFL/Solo system at all.

What about those insertion points? Some manufacturers eliminate them entirely. I view this as needless penny-pinching. The loss in functionality greatly exceeds the small cost in including them.

Some manufacturers are a little more generous and provide perhaps one insert point - if not on all channels, then perhaps the first few. Strangely, this insert point is normally provided pre-EQ, which I find a little odd, as post-EQ is much more useful (especially if you plan on patching in a compressor).

Group inserts are useful - perhaps even more useful than channel inserts - but sadly they are normally amongst the first to be omitted.

A "main mix" insert point is useful, as it allows you to insert a compressor, pre-fade, across the main mix. This sadly is also often removed. However some engineers prefer to have a main mix compressor after the main mix fader - and you don't need an insert point to do this - you can just plug the desk output into a compressor, and plug the output of the compressor into the master mix recording machine.

So that completes our cost-cutting exercise.

Let's now look at a console that is substantially cut-down, but still retains all of the main features that are required.

And now, lets look at a console that is totally cut down, but is still "usable" - albeit with major limitations.

It is possible to cut down the desk still further (and many manufacturers do), but I would consider any further reduction in functionality not really acceptable even for home recording, despite the fact that many such units are commercially available today.

Finally, it is worth noting that if you are building a studio incrementally on limited funds, you don't need to purchase a fully integrated recording console (which you may find too expensive if your budget is extremely limited). You can buy two seperate cheap mixing desks, and use one to recording from (perhaps using it's stereo output as a substitute for two group outputs), and use the other one as your "main" mixing console, to play sound coming "off tape" back through.

Many people on limited budgets use this approach, and if you use some ingenuity in the way you connect the two desks together, you can provide yourself with capabilities that actually exceed those provided on a budget "integrated" console.
Other important considerations
Is Digital Better?

People often assume that digital is better by design. This is not necessarilly so. Remember that all digital circuitry has to pass through some analogue circuitry on its way to your loudspeakers and people rarely complain about that!

The main benefit of digital is that it protects the sound against accidental damage by factors outside of your control. Such factors include (notably) tape "hiss" and "dropout" when recording onto analogue tape. Even in the case of analogue tape though, modern noise-reduction systems offer good protection against added hiss and "modulation noise" and can produce results that some people consider to be sonically superior to digital.

It's worth noting that digital naturally cannot protect sound against deliberate distortion of the signal - the kinds of things you actively want to do when recording. Such distortions include compression (amplitude distortion) and equalisation (spectral distortion), not to mention soft clipping (deliberate and severe amplitude distortion as frequently used for electric guitars).

Most modern mixing consoles are very high performance machines. Their signal paths are clean and introduce very little accidental "damage" to the signal.

Whilst the arguments for digital recording are strong compared to (say) analogue tape, the arguments for digital mixing consoles are much weaker.

Analogue mixing consoles typically offer much more flexibility, are easier to use, and are currently considerably less expensive than their digital equivilents - except in the cases where all the knobs and dials have been replaced with much less friendly "menus" and "dialogs" on a computer screen. But mixing on computer is not a pleasant or simple experience compared to "driving" a good analogue mixing console with real buttons and dials..
Other Required Items

There are a number of important items which people often forget to budget for. Without these, you're unlikely to get the best out of your system.

In addtion to the mixing desk and multitrack recorder, you will need:
A high-quality master recorder to mix onto

This would typically be either a DAT machine or a MiniDisk recorder, or perhaps even a CD recorder. Another respectible candidate is a good Hi-Fi video recorder - provided you also feed it a good video signal such as a video camera with the lens cap on, or perhaps even an off-air picture from television, or you might also use the video output from a home computer, although the stability of such a signal is often poor.

Standard audio cassette is a poor choice, as you master mix recordings will quickly fade over time.

Reel-to-reel can be a good choice if you can find a good quality machine second hand at reasonable cost. You should use a tape speed of 15ips or higher to avoid the same problems that audio cassette has.
Two effects processors

Having two effects processors is not unreasonable, and digital multi-effects units are quite cheap these days. You would normally use one as your "standard" reverb, and use the other for short ambient reverb effects or perhaps stereo chorus or similar
A Compressor

You should consider a compressor as being part of your standard "kit"
An Equipment Rack

You will need an equipment rack to house your effects processors and compressors (as well as some types of synthesizer too). It keeps things neat and tidy and stops these bits of equipment from sliding all over your work surface as you press the buttons and twiddle the knobs. It also hides most of that ugly wiring.
A Patchbay

I survived without a patchbay for a long while. Once I had one, I wondered how I ever got by without. They hide all the ugly wiring and allow you to reconfigure your setup with neat, short cables instead of struggling around the back of all your equipment. They screw neatly into an equipment rack. Best of all, if you carefully design the "normalisation" of the patchbay to automatically make all of your standard connections, you can just pull out every patchcord to reset your wiring to "normal" (whatever you define that to be).

A well designed patchbay can make setting up a recording session a very simple and elegant experience.

I thoroughly recommend the careful design and installation of a patchbay at the earliest opportunity.
Cables and Patchcords

Good cables can be a major expense (typically from sixty dollars upwards for even a moderate home studio setup), but they are well worth it.

It's possible to buy a large quantity of poor quality patchcords and connecting cables at apparently little expense, but it is false economy - I have about ninety dollars of cables which I've later found to be unusable due to their poor quality.

Buy good cables from the outset, and wire your patchbay carefully, and you can forget about ugly and complex wiring setups forever, and your cables will last you a lifetime. Good cables also usually have hand-soldered connectors which you can repair or replace yourself if they get damaged.

Beware of "bullshit" cables though. It is possible to spend too much on cables which are not worth the money. Good jack-to-jack patchcords should cost no more than about six dollars each, long guitar/keyboard cables about ten dollars, and long microphone cables about fifteen dollars.

Some dubious companies even sell "bullshit" optical cables as well, for digital connections! They claim such things as "enhanced stereo imaging". Quite how the fibre optic cable is meant to "understand" or "enhance" the complex multiplexed stereo digital signal format used in digital signal transmission is beyond anyones understanding. Use your common sense.

You can also save money without perfomance loss if you use 15 amp mains cables (such as used to wire up kitchen equipement to the main electricity supply) to wire up your loudspeakers - for a fraction of the cost of expensive dedicated speaker cables - and the performance is identical to most peoples ears.

You can save money sensibly when wiring up a substantial piece of equipment like a multitrack recorder, a mixing desk, or a multi-output sound module (like a sampler) by buying ready-made wiring "looms". These typically have about eight jack-to-jack (or perhaps phono) leads in a thick multicore body and cost about 30 dollars. They make your installation neat and professional, and are tidy and easy to manage when moving equipment around, provided they are not too long.

When laying out your cabling, keep anything that isn't analog audio, away from your audio cables.

Mains cables - and even the low-power leads from mains adaptors - can easilly lead to "hum" on your audio signals.

Personally, I've found it perfectly safe to group MIDI, Digital, and mains cables together, and to keep the audio cables well away from them. Even MIDI cables can introduce noises and clicks into sensitive audio cabling if placed nearby, and in practice, mains cable does not seem to introduce any problems into MIDI or digital cables, so it is OK to physically group them together.