an introduction to mixing

Mixing means controlling the volume level of each sound in a set of sounds to get the desired relative volumes for each so that the final composite sound sounds right. This can be accomplished by changing the amplitudes of the sounds or controlling their individual gain settings. EQing is another technique to use to get the sounds to work in a complementary manner.

audacity manual on mixing tracks: https://manual.audacityteam.org/man/mixing.html

some tips on mixing (especially for music but will be relevant to mixing any kind of audio): https://www.masterclass.com/articles/home-recording-studio-101-how-to-mix-audio

for bonus points, an article on the history of acousmatic music and GRM (summary of an even longer article): https://www.inventionen.de/Inventionen_08/GRMtoMusic.html

simple demonstration of mixing two tracks in Audacity: https://www.youtube.com/watch?v=YCssAU82Pbg

good tips on EQ when mixing: https://www.youtube.com/watch?v=KfG05aJ4yn8