When you use a sound compressor to keep transients at bay during recording, you only want to compress the highest transient levels — the ones that would overload your system or eat up your headroom — and you want to do this so that you don’t hear the compressor kicking in.

Even though every instrument contains different levels of transient signals and each person who plays an instrument creates different amounts of extreme transients when he or she plays, keep the following points in mind as you choose your settings:

  • Keep the threshold high. With a high threshold setting, your compressor only kicks in as the signal gets close to distorting. For most instruments, use a setting of about –6dB. Some instruments with very high transients, such as percussion and drums, can handle a setting like –10dB.

    Set your threshold so that when the extreme transient happens, it triggers the compressor only a couple of decibels, and the nontransient material (the main sound of the instrument) doesn’t trigger the compressor.

  • Adjust the ratio to the material. For high-transient material (such as drums and percussion), choose a higher ratio, and for lower-transient material (like strummed or bowed string instruments), choose a lower ratio setting. Try to use a ratio that relates to the level of the transient over the nontransient signal.

    Because percussion instruments have initial signal peaks (transients) that are much stronger than the body of the instrument’s sound, you can compress this peak without affecting the main sound of the instrument. By matching the ratio to the degree of the transient this way, you can create a more even level without changing the sound characteristics of the instrument.

  • Use a short attack. Transients happen at the initial attack of the instrument. This means that if you want to compress the transient, the compressor must kick in right away when this signal happens. A setting of 1 millisecond or less is optimal.

  • Use a short release. Transients happen quickly, and they last a very short amount of time. When you try to control these signals during tracking, you only want to catch the transient itself — and no other part of the instrument’s sound. Setting a short release time — start with about 10 milliseconds — ensures that your compressor doesn’t linger on to affect the body of the instrument’s recorded sound.

  • Don’t mess with the gain. Because you’re only catching the highest transient signals and you’re only compressing them a tiny bit, you don’t need to add or reduce any of the signal that’s going through the compressor. Leave the gain control at 0dB.

When using a compressor during tracking, keep the following two points in mind:

  • You can always add compression to a recorded track, but you can never take it away. If you’re not sure how much compression to apply to a particular situation, you’re much better off erring on the side of too little because you can always run the sound through another compressor later.

  • If you can hear a change in the sound of your signal, you probably have the compressor set too high. The reason that you use a compressor on the front end is to eliminate extreme transients, which you can’t hear when you play. If your compression setting changes the sound, you should slightly reduce the compression setting (unless you’re going for that effect.