Audio consoles originally gave the ability to control sound volume and placement in a left-right stereo field.  Eventually other devices such as EQ were plugged into consoles and were eventually built into each channel.  Digital versions of mixing consoles have digital versions of these other devices called PLUGINS.

Processing audio can be performed in both subtle and obvious ways.  In some cases processing allows an Engineer to mix a song so that a specific feeling is expressed without being obvious, in others a signature effect is used for its recognition (such as extreme auto-tune).  Processing sounds in specific ways can create a musical genre, such as the Reggae Dub, and can be an extension of the Avante Garde concepts of the studio as an instrument and musical tracks as raw materials.

There are basic effects that are commonly used to process audio beyond level and panning position in a stereo field.

EQ (or Equalization) is a device that allows you to raise or lower specific parts of a sound (bass, midrange, treble, etc).  You can select a range of frequencies and make only those frequencies louder or softer.  An EQ is short for EQUALIZER, which was originally used to equalize problem sounds.  In other words if your microphone was picking up too much of the cymbals on a drum set you would use an Equalizer to turn down the high frequencies and equalize the loudness of the drum kit elements. 

EQs are used to shape sound.  All EQs have common controls such as frequency, width of the range being affected, and increasing or decreasing the selected range of sound.  Every EQ is different, and has a different “sound color” that will make a particular EQ better for a particular purpose.  Do not assume that the same settings used on a different EQ will result in the same sound.

A GATE is an effect that will automatically mute a sound when it becomes quieter than a certain volume.  It was originally used to automatically shut off a channel when there was no loud sound (such as someone speaking) and only quiet background noise. 

You can see how this can be handy on a loud electric guitar that has a low volume humming that is not heard when the guitarist is playing a note.  A Gate would be perfect to automatically mute the channel whenever there was no loud guitar note, only low volume humming noise.  You can set how loud the note you WANT to hear has to be in order to open the Gate with a control called a THRESHOLD.  Set the threshold to a volume that only the notes intended to be heard will reach, and when the sound goes below that threshold (down to the low volume of the humming noise) the Gate will automatically mute the sound.

A COMPRESSOR is used to control how loud a sound gets.  Like the Gate it also uses a THRESHOLD.  When sound gets louder than the threshold, it is squeezed down in volume so the sound only gets a little bit louder.  A Compressor will not only control the range of how louder something will get but also in squeezing a sound make it more dense.  Compressors can be used to make sure a singer’s volume does not jump out of control and to make the sound of a drum in a big room thick rather than airy.

DELAY is also called ECHO and describes when a sound repeats clearly and distinctly.  When there are many repeats as is caused when sound bounces around a large or tiled room the repeats smash together into a long tail called REVERB.