I have tried a few different brands of them for bass guitar and the main problem appears when you play the first note. The compressor uses it as a trigger and after that kicks in, which means that the first note is always louder than the rest. This was really annoying to me. And when you pause for 3-4 seconds or more, again the first note is louder. When you play a slow song with 3 or 4-second breaks between the notes, the compressor practically doesn't work. The second disadvantage for me was that those compressors don't have all the compressor settings. They have mostly volume and sensitivity. Some brands have included also an attack pot, but even when you set the fastest attack possible, the problem with the first note still remains.
The compressors have two main functions: compressor and limiter
First, the compressor function:
When you play bass guitar, it's easy to hear, that not all the notes are with the same volume levels. Some notes are louder, some quiet. There are few main reasons: you can not pul every note with the same strenth of you fingers (which is something normal), each string has a different volume (sometimes is because of the pick-ups)and when the PA system is not set correct. I'm sure, that there are more reasons, but this is not so important in this article.
That's why is developed the compressor. It makes quite notes sound louder and louder notes to sound more quite (of course depend on the compressor settings). Thus, all the notes sound with approximately same volume levels.
Let me say few words about the compressor settings as well:
Threshold: this is the limit, where the compressor starts to kick. For example: if the threshold is set to - 20 Db , every note wich goes over - 20 Db, will be hit by the compressor.
Attack: this is how fast the compressor starts, when the volume level goes over the threshold level.
Release: this is how long the compressor will work
Ratio: (2:1, 3:1, 4:1 etc.) this is how much the compressor will reduce the volume level when works. For example if the ratio is 2:1, and threshold is - 20 Db, when the level goes to - 10 db, the difference between -20 and -10 ( which is 10 db) will be reduced two times and the compressed note will be with level - 15 db.
Gain: the gain is very imporatnt in the compression function, because with increasing the gain, we volume up the quite notes.
Volume: this is the output level of the compressor pedal.
I will show you same of the settings I use:
The settings also depend on the instrument you play. If it's active bass. It has higher output level and you don't need very low threshold,high ratio and high gain level. If the bass guitar is passive and it has lower output level, then you will need low threshold and high gain.
Limiter function:
Of course there are musical styles, which don't need high compression levels. So, then we can use the compressor as a limiter - to reduce only the louder notes, because they can distort the sound and damage the PA system. In this case I use threshold around - 10 db, ratio 3:1 or 4:1 and low level of gain This will guarantee no picks and no distorted sound.
Finally I would like to say something very important to me. When you set the compressor you have to listen to the sound, not only to turn the pots.
