I'll take a crack at explaining the knobs every
compressor and
gate should have. Compressors are used to turn the loudest parts of a signal down in order to allow the signal as a whole to be turned up. The
threshold knob will be on every
compressor. This knob sets the volume at which the
compressor will start doing something. When the volume is as loud or louder than the
threshold is set for the
compressor does something, otherwise it is
passive. Often compressors will have an attack knob that sets how long the signal must be over the
threshold before it kicks in. Once signal is over the
threshold the ratio controls how much volume is removed. A 4:1 ratio means for every 2dB over the
threshold 1 dB of volume will be removed. A
compressor with a 1:infinity ratio is known as a
limiter. It will not let volume exceed the
threshold. The
release knob sets how long it takes for
gain reduction (or compression) to stop and the
compressor to be once again
passive. A lot have an output knob to give you make up
gain for the
gain lost.
Gates have similar knobs. Once again every
gate should have a
threshold knob. The
threshold sets the volume it becomes active again. With gates however it is different. When volume is below the
threshold it does something and when it is above it is
passive. When volume is below the
threshold the
gate turns the sound off. When the volume hits the
threshold for the attack time the
gate opens up and
gain reduction turns off. The hold time sets how long the
gate stays open for once volume gets back below the
threshold. The
release sets the time it takes for the signal to turn back off after the hold time.
Now to illustrate this a
compressor with a -12dB
threshold with a .2ms attack time a 4:1 ratio and a 200ms
release with a makeup
gain of 2dB would do the following.
Nothing while the volume is under -12dB. Once the volume hits -12dB it does nothing. Once the volume has hit -12dB for .2ms the
compressor begins to activate. Should the volume coming in be -8dB the output would be -9dB as it is removing 1 dB for every 4 over the
threshold. It will continue compressing in varying amounts while over the
threshold, then when the volume goes under the
threshold the
compressor continues compressing for 200ms then it would once again be
passive. The entire time if the audio is above or below the
threshold 2dB will be added to the signal.
To illustrate a
gate lets take a
gate with a -24dB
threshold, .2ms attack again, with a 1.5s hold time and a 800ms
release.
The
gate would stop all sound going into it. If the volume is above -24dB it does not let any sound through it unless it is at -24dB or more .2ms or longer. The
gate will deactivate allowing all sound to go through as it was coming in until 1.5 seconds after sound was under the
threshold again. It would then take 800ms to close again and no sound would be allowed through.
For applications, gates are most often used on the tom mics of a drum kit. The
threshold is set high enough that no sound goes through the toms, but low enough for the gates to open up when the toms are hit.
Compressors are more frequently used. I have used compressors on kick and snare drums,
bass guitars, acoustic guitars, vocals,
electric guitars, keyboards, and the main mix. Compressors are your friends when set properly, but the
key with setting a compressor is that you should not be able to hear when it is on. Have you hard the volume of a song change on the radio? That is a
compressor, and it is annoying to me personally. Try playing around with both if you have a chance to. If you have someone who starts screaming into the mic a lot, or a musician that plays quiet then loud they are nice to have.
Sorry the post was so long, but there is a lot to
cover. I think that is most of what you can learn from text though, reading is not a substitute for playing around with them.