Hi.
I use windows 10 and use version 2.3.3
If I have a voice track above and a music track below. Is there anything I have to do to prevent clipping (as now there are two sources of sound)? Or does Audacity adjust that when it’s rendered or all mixed down?
Thanks in advance!
The bouncing sound meter will always tell you what the total sound volume is.
I don’t use the default meters. I change the meter range to 96dB (total digital range) and pull them across the whole Audacity window.
If there is any doubt, you can Tracks > Mix > Mix and Render to a New Track and then inspect the new mix. Audacity doesn’t overload as long as you’re on the timeline, so if you do have an overload condition on the mixdown, you can reduce the volume of the mixdown and then export that. Be sure and select the new mixdown track and File > Export Selected, not regular Export.
Koz
Mixing is done by summation* so you have to reduce the levels. 
There are a few ways to do that before mixing… You can use the Amplify effect, the little gain slider to the left of the waveform, or you can use the mixer (view → Mixer Board). -6dB is 50% so if the peaks don’t exceed -6dB, two channels can’t exceed 0dB (100%). With 4 tracks you’d have to reduce to -12dB. (The actual mix-peak depends on how the peaks line-up.)
And/or you can do it after mixing/exporting… If you export as floating-point WAV (“32-bit float”) it can go over 0dB without clipping. It’s “bad practice” to leave it that way because it will clip your DAC if you play it back at full-digital volume. So, re-import the floating-point WAV and run the Amplify or Normalize effect to bring the levels down.
One advantage to doing it after mixing is that you can adjust the track levels for a good sounding mix instead of trying to “calculate” the levels. (That’s more important with music than something like an interview where both tracks should be the same.)
*Analog mixers are built-around a summing amplifier, and they have a master level control as well as level controls for each input channel. Multitrack DAW applications also have a master level control. But it can still be hard to predict the exact peak of the mix so some people use the same method of re-importing for a separate “mastering” step.
That overload thing is something Audacity does to keep you out of trouble when you’re applying effects, filters, and corrections. Audacity doesn’t run internally at normal 16-bit digital. It uses 32-bit floating which effectively doesn’t overload at 0dB like WAV files do. That means as long as you’re on the timeline, you can fix overloads whenever you want.
Sound files do still overload, however, so you do have to eventually fix it.
Note that you can’t fix overloads by opening up your already overloaded and damaged sound files in Audacity. That’s why overload/clipping during recording is one of the sure-fire ways to kill your show.
That’s also why home microphones almost always come out of the box with low volume.
Koz