Distortion if tracks added

I have recorded 4 tracks which sound perfect
on their own if others are muted. If I unmute
others in some combinations the sound is distorted
like clipping. Also the output level meter is in
het red then.
What can I do?

It is clipping… :wink: Mixing is done by addition (summation). Analog mixers are built around analog summing amplifiers. 6dB is a factor of two, so depending on how the peaks line-up. mixing two files could boost the peaks by 6dB.

There are a couple of ways (at least) to handle this -

  • Reduce all of the files by 12dB before mixing. Then if the mixed file it too quiet (depending on how the peaks align) you run the Amplify effect to bring-up the level on your “final mix”.

  • Or go-ahead and mix them “normally”, and export to 32-bit floating-point WAV. (Floating-point won’t clip and Audacity uses floating-point internally, although your digital-to-analog converter will clip if you play a file that goes over 0dB.) Open the floating-point file and run the Amplify effect to bring the peaks down to 0dB, then re-export in the format of your choice.

I tried lowering the individual track volume
controls what works. Have to make a habit
of amplifying each track to -6 db direct after
recording, solves the problem.

Have to make a habit of amplifying each track to -6 db direct after recording, solves the problem.

With 4 tracks, -6dB may not always be enough. Worst case, 4 tracks peaking at -6dB can sum to +6dB. And realistically, you probably don’t want to mix the tracks at exactly the same level… You usually want to mix for whatever sounds best.

But if you do go over 0dB, you can always use the 2-step method of rendering (exporting) to floating point and then re-normalizing. And, because you can’t exactly-predict the final mix level, it’s not unusual to do an extra “mastering” step anyway

FYI - DAW software (REAPER, SONAR, Cubase, etc.) makes this easier with level controls for each track as well as a master level control (like an analog mixer). And, with a DAW you can “automate” the levels similar to Audacity’s Envelope tool, so for example you can fade-up the guitar during the guitar solo and fade-down parts of a track that are too loud, etc. But even with a DAW, you might end-up doing a final mastering step. The downside (besides the cost) is that these programs are at least 10 times as complicated as an audio editor like Audacity.

what audacity does is deviding all
track volumes by the #tracks and
then mixes (adds) them.
This should alway stay within 32 bits
boundaries if 32 float format.
Obviously it has some flaw doing that.

There is no flaw, Audacity just doesn’t do the maths for you (it’s a feature request).