Mix and render problem: first channel gets over amplified

Hello all:

I have a mix of prerecorded music and my introductions as voice on three channels:

[My voice][prerecorded music]
-------------------------------------[My voice][prerecorded music]
--------------------------------------------------------------------------[My voice][prerecorded music]

The first channel’s volume is a bit high relative to the others but it is not clipping. The other two channels are well within the 1,-1 limits.

When I mix and render the three channels, the resulting single channel ends up go 14 units beyond 1,-1 limits for the lenght that correspond to the first channel.

I reduced the amplitude for the first channel well below the maximum for the second and thirs channels, but I still end up with grossly amplified channel for the lenght of the first one.

What is going on?


[I am on Windows 7 Enterprise, running Audacity 2.0.5]

Mixing is done by addition (summation). Analog mixers are actually built around summing amplifiers.

Adjust the relative volume of the individual tracks until it sounds right. Audacity itself uses floating point, so there is no upper limit and audio data won’t actually be clipped until you save the audio file. (You may have to reduce the master playback volume so that you don’t drive your DAC into clipping.)

After mixing (but before saving) run the Amplify effect and bring the peaks down to 0dB. Now, when you save your file it won’t clip.

To adjust the relative volume of the tracks, use the gain sliders on the tracks until you don’t see clipping in Meter Toolbar.

Amplify tells you nothing about the summed volume so it is better used after the render in my opinion, to judge the final export level.


I think the complaint is that they don’t add up in a well-behaved manner. The top track’s volume goes up more than the other two.


Kozikowski understood the issue.

There is no clipping before the mix and render with channel one. Audacity somehow brings the amplitude way up. It should not. Over the past few years I have done hundreds of mix and renders and it is the first time I am running across this problem.

The issue doesn’t make sense, unless you have the gain slider turned up on the first track, or unless the other tracks have content where the length of the first channel is. What are the dashes in your drawing?


The way I understood the illustration, the dashes are silent stretches and should not contribute to the show. When exported to a single sound file, the Project should produce three short performances one right after the other. We assume they were recorded at roughly the same volume.

I do have a question as to where you got the silences. Were they just a live microphone with you off quietly making fresh coffee in the kitchen, or did you make the silences using trickery?

And yes, moving any of the sliders to the left of the tracks may create a result you weren’t expecting. It’s possible to bump those by accident and what you think you told Audacity to do and what you actually told it are different.


Dashes indicate no sound/no content.

The silent stretches have no sound at all. I simply moved the tracks with “Align End to End” menu item, which created these long stretches of silence for track 2 and 3.

I don’t have audacity installed on this computer, so I will try to figure out what “sliders” are. Who knows, I may have done something wrong. I’ll check it in the evening.

I solved the issue by copying the contents of each channel manually, and creating a single channel.

When I exported this single channel, the resulting mp3 also sounded fine. In other words no over amplifications for the first channel.

I think there is a bug in Audacity…

Thanks for getting back about the problem. So you mean, pasting each track end-to-end?

I can’t reproduce a problem with three tracks as you described.

Can you make an Audacity project for us that would reproduce the issue as soon as we mixed and rendered it?

If so, use File > Check Dependencies… and copy in any dependent files.

Undo to the stage just before you would mix and render.

Save and close the project and zip up the AUP file and _data folder.

Upload the ZIP file to dropbox, dropsend or other service like http://www.mailbigfile.com/ then give us the URL of the file.