How to Use a Compressor Pedal
Compressor pedals are disarmingly simple – they detect spikes in your volume and normalize the levels automatically. Fattening up your tone, boosting sustain and making your sound punchier are pretty much just possible side effects of the volume controlling process. It’s all a trade-off between the desirable and undesirable side effects, so to get the most out of any given pedal you need to understand the various controls and what they do.
The input level control on compressors enables you to control the range of signal the pedal responds too – if you set it wrong your result will be way too noisy. If a pedal doesn’t have the control, you’ll need to use a volume control on your guitar, pre-amp or another pedal to control how loud signal going into the compressor is.
The threshold is the point where your pedal starts to actually compress your tone to control the volume. If there’s no knob, it’ll be set at a fixed amount, which you can only affect by adjusting the input level.
This controls the amount your volume is decreased by (in dB), so a ratio of 4:1 means that once you go over your threshold, each increase of 4 dB in input is reduced to just 1 dB of additional output volume. If this isn’t available, your pedal has a fixed ratio.
This controls how quickly the compressor responds to your signal, and is often accompanied by a release control which governs how long it takes before the pedal stops compressing. While other controls may be missing, many compressors like the MXR M-132 and the Boss CS-3 have this option.
Compression reduces your average signal level, so the output control is there to let bring it up to the desired volume again.
Finally, some compressors only have two controls, “Compress” (or “Sustain”) and “Level.” Level is just an output control, but compress could control the ratio, threshold or other parameters like signal gain. If there are unfamiliar controls on your compressor and you can’t get the sound you want – consult the manual before giving up on compression effects!
If you want to read my in-depth reviews of some of the best compression pedals available, you can find the reviews here: CompressionPedalReviews.com