An Introduction to Compression: Basic Compression - A Free Guide from Audio Masterclass

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Can I send the output of my mixer to a compressor then bring the signal back to the mixer?

An RP reader has worked out an interesting way of connecting his compressor. Will it work? Or is something going to blow?


A question from an Audio Masterclass reader...

"What's wrong in connecting the main outputs of a mixer to a compressor and return the signal to mixer inputs for equalizing, instead of connecting through inserts? It sounds unorthodox, but is there any serious difference in sound?"

It looks like we're in the analog universe here. But that's OK, the analog universe still exists; it hasn't imploded into a blob of dark matter just yet.

It is often interesting to compress the entire mix, rather than only individual channels. You have to know what you're doing so it is advisable to conduct a lot of experiments before committing the best song you ever wrote to this treatment.

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Some mixing consoles make compressing the mix easy - they have insert points in the stereo master outputs.

"What's an insert point" comes a small voice from the back of the room.

Mixing consoles often have an insert point in each individual channel. The signal can be tapped off at this point and processed, often through a compressor. The signal is then reinserted into the channel's signal path. Normally only the processed signal is used; there is no mixing of processed and unprocessed signal as there would be when using auxiliary sends and returns.

Although many mixing consoles have channel inserts, fewer have inserts in the master outputs (or the group outputs either).

But that doesn't mean you can't compress the mix. All you have to do is connect the compressor between the master outputs of the console and the inputs of your stereo master recording device. That will work just fine. Remember to click the 'stereo link' button on the compressor.

But what if you want to compress the mix, and then EQ it? There's absolutely no reason why you shouldn't do this, if you want to. But how?

With a DAW this is dead easy, but we are not talking about DAWs. We're in the analog universe, remember?

So what would happen if you connected the outputs of the console to the compressor, and then brought it back to a pair of channels for EQ? (You would need splitter cables so that you could also connect to your stereo master recording device.)


You have just blown your speakers.

The reason for this is that you have just created a perfect circle from mixer output back to mixer input back to mixer output again. This creates a positive feedback loop in which signal will build and build all the way up to maximum level. If you don't at least blow your tweeters then you have been lucky. But it wouldn't have been pleasant to listen to.

So don't do this.


Be very careful in what you do.

The one thing you must not do is route the compressor return channels to the master outputs. That's what caused the positive feedback loop.

But if you don't do that, how can you get the EQ'd signal out of the mixing console and into your recorder?

Well there are a number of ways.

If you have individual channel outputs then you're laughing. It's easy, but not so many consoles have this feature.

Another way would be to take signals from the insert points of the compressor return channels. This would only be useful if the inserts are post-EQ. If they are pre-EQ, then you won't get the equalized signal.

If you can't do this, then you would need to find a couple of spare auxes that you are not using in the mix. Assuming the auxes are post-EQ, then this will work. It's just a bit fiddly.

There are other alternatives that involve recording the compressed signal, then EQing it and re-recording it.

Of course the simple answer would be to buy a DAW, where this process is easy. But that's not the point. One of the skills of a good engineer is to find alternative ways of doing things. Finding a different way to other people is an excellent route towards creativity.

By David Mellor Sunday February 21, 2010