Hi, I’m curious about compression. Can you tell me more about it and how to use compression with guitars?
– Nick, Toronto
Hi Nick, that’s a great question. Fuzzboxes, overdrives and tremolo pedals make an obvious difference, but compression can be subtle to the point of inaudibility. However, that doesn’t mean compression isn’t useful or even indispensable for certain sounds and playing styles.
Although their amplifier electronics can give compressors a ‘sonic signature’, changing the tone is not their primary function. Instead, they alter a signal’s dynamics while leaving the frequency balance, harmonic content and distortion levels unchanged.
In simple terms, a compressor might be described as a volume control that automatically turns itself down when the input signal exceeds a pre-specified threshold level, and resets itself when the input level falls back below that threshold.
The speed at which the compressor responds is known as the attack time and the speed at which it resets itself is known as the release time. Compression strength is the amount of attenuation applied to the peaks.
Studio vs stompbox
Stompbox compression is used before the amplifier, but studio compression is always applied post-amp, virtual or otherwise. As well as having greater sonic transparency, studio-style hardware and software compressors tend to have more sophisticated and comprehensive controls. You can set the attack and release times, threshold level and the amount of compression.
Anybody with a DAW installed on their computer or mobile device has access to studio compression – whether you’re using compressor plugins packaged with a DAW, or exacting vintage emulations. Many provide virtual stompbox compressor plugins too.
Most classic guitar compressors had very few controls. At best you could expect a compression control – sometimes labelled ‘sustain’ – and a volume control to compensate for any perceived drop in level. Some modern compressor pedals now offer studio quality audio and controllability. The Origin Effects Cali76 is an obvious example, since it’s based on a classic UREI 1176.
So how is compression used? To answer this, let’s examine how compression is utilised in different musical genres.
Many country pickers have dazzling technique but compression is invaluable for making notes pop in an incredibly uniform way, and getting those lightning-fast runs smooth as smooth as sippin’ whiskey. Country compression is often far from subtle, but you’ll need a compressor that has a transparent tone.
A medium amount of compression should be applied and we suggest a medium attack time to allow some picking dynamics to come through. Medium-to-slow release times also work and you may want to raise the output slightly to restore the level or maybe hit the amp a little harder. A compressor in this context provides much of what you’d want from an overdrive, but without adding distortion.
Sustain without gain
By applying compression with a hard knee or fast attack, you can eliminate the peak at the front of the note altogether. You may even knock the level below the compression threshold, which means you’ll have to boost the compressor’s output. The sustain trick is achieved by adjusting the release time so that the compressor output is increasing at roughly the same rate that the input signal is decaying.
Classic examples of this type of compression include Jeff ‘Skunk’ Baxter with Steely Dan and the early recordings of Mark Knopfler. David Gilmour’s solo on Another Brick In The Wall (Part Two) takes this approach to the extreme – you may need to chain two compressors together to get a similar effect.
In the details
Studio compression is generally used more subtly to help guitar parts sit in the mix and to enhance details. By gently narrowing the dynamic range, a compressor can ensure that loud parts don’t jump out and quieter bits can be heard. This sort of compression can also help if a player’s technique leaves something to be desired, and there’s nothing to stop you setting a stompbox compressor to do the same.
We suggest medium or slow attack and decay times, with a low compression ratio. When you get this one right, it’s the kind of effect that you’ll only notice when it’s turned off, and it’s particularly useful with narrow single coils that tend to have a faster and more dynamic response than fatter single coils and humbuckers. It also helps if your compressor has a blend control to balance compressed and uncompressed signals. This is sometimes called parallel compression.
Bringing drive alive
Players often wonder where compression should be placed in the signal chain. There are no absolute rules but for most purposes we suggest early is better than late. If you use overdrive, fuzz or clean boost pedals to lift the level for soloing, it makes sense to place your compressor before all of these.
If you don’t, much of the boost provided will be negated by the compressor. You’ll have to run your other pedals harder to compensate, and you may end up with more noise and distortion than you really want. Putting a compressor before an overdrive may also produce more creamy sustain than you can get from an overdrive pedal alone.
Alternatively, you can set your overdrive pedals to the same level as your clean tone and place the compressor at the end of the chain to use it as a clean boost and sustain enhancer. You can also push valve amps into overdrive and use a compressor to lower the volume hitting the amp. The compressor provides some tube-rectifier-type sag as it cleans the amp up. When the compressor is bypassed, the amp overdrives and provides more than enough compression on its own.
Funk players often alternate between strumming chords and playing single notes, but both need to maintain a pretty even volume level. To achieve this, you may need a higher compression ratio than a country player would use, along with faster attack and release settings. Compressors with blend controls are very popular for this style of playing.
Metal guitarists often need compression for similar reasons to funk players. However, the situation is complicated by greater dynamic range, a wider frequency spread and problem frequencies, which can be caused both by equipment and the prevalence of dropped tunings.
Chugged chords often generate a massive amount of bass content, which isn’t apparent when players switch to single notes or higher chord inversions. Therefore, a one-size-fits-all approach to compression doesn’t always work.
For this reason, compression is often left to the mixing stage and producers may choose to apply multi-band compression, where the compressor’s response can be tailored to specific frequency bands. This provides very fine control of the low frequencies without adversely effecting the low and upper mids. In this context, compression can be used to retain clarity and punch in the bass without losing the power and cut of guitar tracks.
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