Sends are an interesting component of mixer topologies. They allow a combination of mixing and parallel processing. When several channels have non-zero gain applied to a send, they are mixed together, sent through whatever processing is assigned to the send, and then returned on a new channel. The processing on the send ‘hears’ a mix of all the channels being sent to it. As the output of the processing is returned on a separate channel, it does not affect the original source channels. It also means this return channel can be managed separately to the other channels in the mixer.
The most common uses for sends is to add ambience to a mix using delay and reverb. This works particularly well for two reasons:
- The ambience is added ‘behind’ the sound, so that the original sound doesn’t need to be altered. This takes advantage of the parallel processing aspect of using sends.
- Reverb and delay are usually gain-linear, meaning they do not change their sound with different input levels. Sending a quiet signal to a reverb will produce the same reverb sound as sending a loud signal to it (the only difference being the output level). Additionally, sending two different sounds to a reverb simultaneously has the same result as sending each sound on its own. This takes advantage of the mixing aspect of using sends.
Of course, reverb and delay aren’t the only types of processing that can be used with sends. Modulation effects such as choruses, flangers or phasers are also common. They work because they also take advantage of the characteristics of sends – they work by adding a sound to the original sound, and they are gain-linear – they work the same way regardless of what the input level is.
Increasingly, it is becoming more common to hear of people using non-traditional types of processing with sends. Interesting things happen when using processing like compression and saturation on a send, because these processes are fundamentally different to additive, gain-linear processes like reverbs, delays or modulation.
The first thing that happens when using compression or saturation on a send is that the processed audio is mixed in with the unprocessed audio. In the case of compression, this will get you parallel compression – which usually requires two duplicate tracks or a specially-designed compressor with a wet/dry control. In the case of saturation, this adds some saturated sound to the original without significatly damaging the integrity of the audio.
The other thing that happens is that you have an opportunity to use the send as a kind of parallel bus. That is, you can send audio from several channels to a single compressor or saturator (which is then brought back into the mix in parallel with the original sounds). It’s important to remember that it is a bus. For example, you might set up a compressor on a send, and send some kick and bass to it. Unlike a gain-linear process such as reverb, the compressor will respond differently to the kick and bass playing together than it would to the kick or the bass separately. The other thing to watch is that the compressor will respond differently depending on how much of the audio is sent to the compressor. Typically, the audio will be more compressed if more of it is sent to the compressor. Similarly, the audio will be more compressed when there are more active audio channels being sent to the compressor because the overall level sent to the compressor is higher. This can make mixing rather complex.