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An Audio Masterclass learning text.
There are two reasons why a large mixing console with many channels is desirable. The first is obviously for when you need to mix a lot of channels. A large jazz orchestra for example may have a microphone for almost every instrument, or at least one mic for every section of instruments, plus soloists. The other situation that calls for a lot of channels is where you need alternative setups readily to hand. This occurs in live broadcasting where you might have one group of channels for the presenters and guests, and another group of channels for a live band. You wouldn't be mixing both simultaneously, but it is important to have everything set up and ready.
How many channels are enough?
When choosing a mixing console, you will often find that a particular model of console comes in different sizes with different numbers of channels. 16, 24 and 32 are common options. It is important to choose the correct version. Buy one with too few channels and you will struggle; buy one with too many and money is wasted on channels that will never be used. A good rule of thumb is to calculate how many channels you will use in everyday situations, then add eight. Those eight channels may only be used rarely, but at least you know they are there. And if you have a project that you could have wished for a larger console to handle, then you'll just have to compromise. Many sound engineering tasks involve compromise and the ability to get a satisfactory result is the mark of a good engineer.
Console expansion units
Some mixing consoles have optional expansion units, so you can buy a smaller console initially, then add extra channels later. This is a good idea with only one problem... what if the manufacturer decides to discontinue the console, or perhaps just the expansion unit, from their line of products? So buying a console with the idea of expanding it in a year's time is an act of faith. You are reliant on the manufacturer still having the expansion unit available. Secondhand expansion units will be rare. It would be very unlikely for anyone to sell an expansion unit without selling the console too.
Combining two consoles
It isn't the most elegant of solutions, because parts of one console will remain unused. However, to gain more channels it will be a very effective option to combine two mixing consoles. To do this for a simple stereo mix, take the main stereo outputs of the first console and connect them to two channels, or auxiliary returns, of the other console. Set the faders of these channels or aux returns to 0 dB so that they are at unity gain and do not change the level of the signal. Route these to the main outputs of the second console.
Now you will be able to mix with the full number of channels of console one plus console two, minus the two channels or auxes of console two that you used for the outputs of console one. So if you had two consoles, each with 24 channels and 4 auxiliary returns, you can combine them to give 48 channels with 6 auxiliary returns.
The consoles do not have to be identical, nor even from the same manufacturer.
Naturally you wouldn't expect this to be as good a solution as having one large console. The principal drawback is that the solo system won't be fully functional. Normally, when you press the PFL or solo button on a channel, you hear that channel alone through the monitors. All the others are muted. But now, if you press the solo button on a channel on console one, you will hear that channel plus all the channels of console two! The solo system on console two will work as normal. The workaround is this... When you press a solo button on console one, also press the solo buttons for the channels on console two to which console one is connected. You have to press three solo buttons rather than one, but you will soon get into the habit of doing this.
It is perfectly feasible to combine two consoles to make what is effectively one large console with lots of channels. The drawbacks are few and you have the flexibility to use the consoles separately on different projects if need be.