Why do mixing consoles have so many channels on them?

Question

Why do mixing consoles have so many channels on them?

Answer 1

because they are mixers, and they have to mix each channel and give resultant output.

Answer 2

Each instrument or person singing into a microphone is brought into the mixer on its own channel.  This way you can control the tone (treble, mid range, bass) and volume of the sound for each channel individually.  The end result is that each component of the musical sound has the correct tonal qualities and is at the proper volume for the final mix of what the audience hears.

The mixer also sends sound from each channel back to the people on stage so they can hear themselves or other parts of the music to help them play.  This is called a monitor mix and can sound very different from the FOH (front of the house) mix that the audience hears.

Mixers also add effects to certain instruments but mainly vocals such as reverb to enhance the sound.  This is controlled at each channel.

In short... a mixer is all about controlling and shaping the sound.