USING A HARDWARE MIXER
Using A Hardware Mixer With Your Computer
Technique : Recording / Mixing
Figure 1. A computer audio system with a two-in, two-out audio interface. |
Paul White
Although it is possible to compose and mix music entirely on a computer, most practical music recording systems include some external hardware elements, which is where life can get confusing. For example, you may wish to use a high-quality signal from a capacitor microphone rather than relying on your soundcard's mic/line inputs and bundled plastic microphone, which means either using a separate recording channel or mixer. This important subject area was covered in detail in SOS April 2002, although the use of a mixer in this capacity is also covered briefly here. What may be less easy to sort out is the best way to integrate external MIDI instruments and effects boxes into the system.
A Simple Monitoring Setup
For users with a simple stereo-in, stereo-out audio interface, the solution shown in Figure 1 is both simple and affordable. Small desktop mixers are no longer high-cost items, and even a modest mixer provides a convenient means to combine the outputs from your soundcard and the outputs from your external MIDI sound sources. The number of inputs required depends on how much hardware you want to plug into them, but you don't need mic inputs on every channel. Because systems have a habit of growing, try to get a mixer with a few more channels than you currently need.
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A conventional hardware effects box can be used via the post-fade aux sends and aux returns of the mixer and this allows you to add different amounts of effect to each sound being mixed. However, what you have to bear in mind when using a soundcard with stereo outs is that all the computer audio tracks (and maybe some MIDI parts too if you're using your soundcard's synth chip) emerge ready mixed, so there's no way to add hardware effects to some tracks of your computer audio mix and not to others. Because of this limitation, your computer audio tracks need to be treated using plug-in effects and processors before they are sent out to the mixer. The MIDI tracks may or may not have effects available to them depending on the design and type of soundcard you're using.
Connecting A Microphone
Provided that you have one spare mixer channel with a mic input, you can use it to feed a signal into the computer for recording, thereby saving the expense of a dedicated voice channel or stand-alone mic preamp. In many home studios, vocal and instrumental parts are overdubbed one at a time, so a single input is often sufficient. On a standard mixer with no multiple busses or other fancy routing options, the easiest way to use a mic channel for feeding a soundcard is to turn its fader fully down and then use the pre-fade send control to send the mic signal to the mixer's pre-fade output jack. This is normally used to set up monitor mixes, but in the smaller studio it can be fed directly into the soundcard input as a means of routing the mic signal separately. Essentially, the mic signal goes through the mixer channel, via the pre-fade send and out of the pre-fade send jack without interacting with anything else the mixer may be doing, almost as though it were going through a separate piece of hardware. All you have to do is keep its channel fader down when mixing and ensure that the pre-fade aux send is turned down on all other channels when recording.
A further tip here is that you can turn up the mic channel fader when recording to hear the mic signal in the stereo mix (which you'll need to monitor via headphones while overdubbing). By monitoring the mixer channel in this way and by switching off 'through monitoring' in the computer, you'll avoid the distracting effects of any system latency, though you'll also lose the ability to monitor the effects of any software plug-ins being applied to the input signal.
Using A Multi-output Soundcard
Figure 2 shows a slightly more flexible solution for users with multi-output audio interfaces. If you have eight physical analogue outs, these can feed eight inputs of your analogue mixer, and because these eight signals are independent of each other, different amounts of effects can be applied to them. Furthermore, the mixer insert points may be used to place signal processing devices, such as compressors or equalisers, into individual signal paths.
Figure 2. A computer audio system with a two-in, eight-out audio interface. |
One important point to note is that when you're using an external mixer with a multi-output audio interface, the panning assignments on the computer's internal mixer are more likely to be used for routing than for actual panning. In the example where the lead vocal is on the first output, this would be achieved by assigning the signal to interface outputs one and two, then panning the vocal channel hard left in the computer's mixer page so that all the signal is routed via the odd-numbered soundcard output (ie. number one). That's because the routing in most software mixers follows the hardware mixer convention of using the pan control to adjust the balance between odd/even-numbered output pairs. When the vocal signal reaches your hardware mixer, it is simply a mono source that can be panned anywhere you like in the mix using the mixer's pan knob. Where stereo mixes have been set up in the computer using an odd/even output pair, the hardware mixer channels into which these are routed need to be panned hard left and right to maintain the original stereo perspective.
The pre-fade send trick used to get a mic signal into a computer soundcard works exactly the same as described earlier, but if you want to record more mics onto separate tracks at the same time, you'll either need a mixer with more pre-fade sends or you'll want to use channel direct outputs, where fitted, to send the channel signal directly to the soundcard input. For any larger-scale projects, a recording mixer with multiple output busses is recommended.
Summing Up
Because there are so many good software plug-ins available today, using a two-in, two-out soundcard or interface doesn't impose too many restrictions on how you can mix your tracks. Even so, it does preclude you from using hardware effects and processors to treat individual parts of your mix, other than elements coming from external hardware such as MIDI modules.
An audio interface with eight outputs offers a good compromise between flexibility and cost, as it allows you to separate important sounds for processing with external effects and processors. In each of these cases, although it need not be large or expensive, an external mixer is still needed to combine the sound outputs of your computer with the outputs of external MIDI hardware instruments.
Published in SOS June 2002