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Compression Theory- the fundamental purpose of a compressor is to reduce the dynamic range of a signal so it fits better into a mix. It’s effects can make a track seem louder, and change the timbre of the sound being compressed.

Threshold- is the point at which the compressor starts to work.

Ratio- the amount of reduction that takes place after the threshold is exceeded. Expressed in a ratio like 3:1 or 4:1; in a 3:1 ratio, if the threshold was exceeded by 3 dB it would be reduced to 1 dB and in a 4:1 ratio, if the threshold was exceeded by 4 dB it would be reduced to 1 dB. This also stays the same no matter how much the signal is exceeded; for example a 3:1 ratio, if the signal was exceeded by 6 dB it would be reduced to 2 dB. A 4:1 ratio, if the signal was exceeded by 8 dB it would be reduced to 2 dB.

Attack/Release- Determines how fast or slow the compressor kicks in after exceeding the threshold and how fast or slow the compressor turns off after exceeding the threshold.

Knee- usually hard or soft. A hard knee is when a compressor turns on right after it exceeds the threshold. A soft knee is when a signal starts to be gently compressed when it starts to approach the threshold. This way the compression is more gradual, usually starting with a 1:1 ratio until it reaches the selected ratio. 6-9 dB soft knees are supposed to be the best for instruments such as string, brass, and wind instruments.

Peak/RMS- if not specified the compressor will probably be a RMS compressor. Some compressors offer these options. RMS compression works on an average signal level and usually does not respond to fast transients where a peak compression works with fast transients. For drums use peak and on all other instruments use RMS. Most instruments are discerned from their transients and a Peak compressor can alter the transients making instruments besides percussion to sound dull.

Gain(make-up-gain)- Brings the signal up to a pre-compressed volume.

Side Chaining- uses a signal rather than a threshold to compress a signal. It’s good for making pumping synths and doing voice overs on movies and radio. Key and Link- The Key triggers the compressor. For example if there is a duet of singers. Using one of the vocals (vox) to trigger the compressor of the other vox. This way when they are singing by themselves the compressor won’t be working but when they both sing the compressors will be on. It’s kind of like automatic mixing.-

Hold Control- if present this determines the minimum amount of time that the compressor will be working. It can help if there is a signal that dips above and below a threshold and causes an unwanted pumping sound.

input filter- addition eq for the compressor. On high end units. It eqs to compressor, it’s not like a an extra eq for the sound but just for how the compressor works. Kind of like a multiband compressor function. If a highpass filter is on the compressor won’t be triggered below the highpass filters cutoff.

Vocals- 2:1, 2.5:1, 3:1 Compress the signal around 3dB. This will be 3dB of gain reduction. Fast attack and mid to slow release. Soft knee around 3-5.

Bass- ratio of 5:1 6:1. Probably a hard knee 6dB of compression. Fast attack midrange or slow release.

Fast- 0-30ms mid- 30-70ms, 70-120ms slow

fast 5-128, mid 128ms-1second, slow 1second and above

Too fast attacks and releases create pumping. Can use compressors to help improve other things besides dynamic range. Removing extra dB can help smooth a vocalist out. Using proper eq and compressors will significantly reduce to labor of mixing. Things will kind of help themselves. When recording, it is best to not record effects with the original signal but to instead mix them in later. An exception to this would be distortion on guitar or maybe a small amount of compression on a bass guitar. When compressing drums make sure that there is no over compression. On a four on the floor drum loop make sure that the compressor goes back to 0 dB between each kick hit.