Practical audio theory – Stereo or mono

Here’s a philosophical thought for you: If you save a recording as a ‘stereo’ file, it’s not always stereo.
It’s not just a matter of ticking the ‘stereo’ box.

Suppose you record a piano. You use 2 microphones. Everything the left microphone picks up is sent to the left speaker and everything the right microphone picks up to the right speaker. Now there are differences between left and right, for example because the left microphone picks up more of the low strings of the piano and the right mic more of the high strings. These small differences make the recording sound stereo.

 

If you would record this piano with 1 microphone, the recording is mono. You can later choose to save this recording as a stereo file, but then the sound of the same microphone will be copied to both the left and right channel. Because both channels are now exactly the same, the recording will sound mono. There are no differences between left and right.

You can hear this very well when you’re sitting right in front of your speakers: the sound seems to come from the spot exactly in the middle between the two speakers. If so, your recording is mono. Even if you saved it as a stereo file. Listen to the difference in sound between these two files (when sitting right in front of your speakers or with headphones on):