When stacking compression, we’re creating a series in which multiple compressors are performing distinct jobs. For example, we can stack multiple forms of peak compression, or combine downward and upward compressors - additionally, we combine distinct sounds like the 1176 or LA2A optical compressor to create something entirely unique.
When we talk about stacking compression, we’re mainly considering putting compressors in a series, or using one compressor and then another back-to-back. When it comes to parallel compression, the signal is separated into a new track which is compressed, and then joined with the original.
With that out of the way, let's listen to some stack or series compression, and then look at some techniques you can use on your mixes or masters.
Vocals are a great instrument on which to use series compression - typically I find I’ll use a little bit of 2 compressors for different purposes. For example, I could use a classic compressor with a quick attack and release to capture the vocal and control it quickly.
Then I’d use an optical compressor to create a smooth sound, with a longer release. So the first one controls the vocal but keeps its detail, and the second is more for affecting the timbre and feel of the vocal.
What’s cool about modern compressors is that you can use them in parallel and series simultaneously. To do this I’ll place 2 compressors in my chain back-to-back to achieve series compression, and then I’ll affect their wet/dry or mix dials to achieve the parallel aspect.
Let’s try this with the vocal example we just covered, and play with the wet/dry dials until we find a balance we like.
Stacked compression works well when we use different types of compression, like RMS, Peak or Downward, and Upward. RMS will compress downward from the waveform’s average loudness, peak will compress downward using the waveform peaks for detection, and upward will increase the signal from the noise floor up.
So we can control the signal from the peak of the waveform down, about the middle of the waveform down, and from the quietest part up.
If we stack mid-side and then left-right compression, we can get some really interesting sounds. The mid-side compression will cause stereo expansion whenever the mid is compressed, but the side isn’t, well left and right compression will cause a dynamic relationship between the 2.
To create more of a dynamic between the left and right we’ll delink the channels so that they can they’re treated independently. Let’s listen to what this does on a mix bus.
If we’re using series compression, we can place an EQ between the 2 to either drive frequencies into the second compressor, or pull back a little so that certain frequencies are triggered as much. We can even place an extra EQ after the second EQ to compensate for the changes.
This is called an emphasis de-emphasis technique , but we can use it in the context of series compression to first control the dynamics, then create a specific tone with the second.
Similar to series compressors, we can use series saturators to both compress and distort the signal in two unique ways. For example, I could use a tape saturator to add soft-knee compression and then tube saturation to create a different non-linearity, in addition to unique harmonics.
This way we can combine compression, and complex harmonic formations.
Some compressors have very distinct sounds like the 1176 or LA2A - if we put these very recognizable compressors in series, we can combine their tones to create something new. For example, I could get some mild distortion and punch from the 1176, and then a thick sound from a retrotube emulation.
There are more examples of this, but these are some of the more recognizable compressors sounds out there.
