change in balance from stereo to mono

[Jkjammers]

I edit songs for dance recitals and have been told it is safer to change the songs from stereo to mono in case the high school sound system isn't very great. This would avoid the problem of possibly only hearing either the left or the right side. Recently I was editing a song and when I changed the format from stereo to mono, some of the instruments were slightly turned down and lost their punch. I always thought that when changing a song from stereo to mono, the two sides just overlapped and became one, thus the balance of the instruments would not change. Am I incorrect about that? Is there something I can do? In case this matters, I use the 1.3.12 version of audacity.

Jamie

[steve]

I always thought that when changing a song from stereo to mono, the two sides just overlapped and became one, thus the balance of the instruments would not change.

Usually that is correct, but there can be complications (as you've just discovered).

Here's a little experiment that will demonstrate the problem.

1) Record or import a short audio track.
2) If it is a stereo track, convert it into a mono track (Tracks > Stereo to Mono)
3) Duplicate the track (select the track then Ctrl+D)
4) Select the duplicate track only and apply the effect "Invert" from the Effects menu
5) Press PLAY - there will be no sound
6) Mute either of the tracks and you will hear the other track normally.

What is happening here is that one waveform is the exact negative (inversion) of the other, so when they are played together they will in effect "cancel each other".

Another way to describe "inversion" is to say that the waveforms are "out of phase" (in this case "180 degrees out of phase).

A similar thing can happen with "normal" stereo recordings. If there is a "phase shift" in the sound of any particular instrument between the left channel and the right channel, then when the tracks are mixed to mono there will be a partial cancellation of the sound from that instrument.

This is another reason why it can be a good idea to make your recordings into mono if you intend to play them on a mono PA. Some PA systems will play the full stereo recording, but mix the two channels into mono and cause the effect that you have noticed. By preparing the tracks as mono recordings beforehand gives you the chance to avoid this problem.

Unfortunately there is no way of knowing in advance if this will be a problem or not. The only way to be sure is to make the stereo tracks mono and then listen to them.

If there is a problem, then a possible solution is to just use the left or the right channel of the original stereo track. To do this, click on the name of the track and from the drop down menu select "Split to Mono". Then delete the mono track that you don't want. (You can use the "Solo" button to preview each track and decide which one sounds best).