Audacity3.0.2 compressor error

An internal error if the beginning of the sound is a negative time was improved.
However, if the beginning of the sound is a negative time, the compressor will move the truck time shift even if I have locked the track sync.
macOS Catalina.

Thanks for confirming

I can’t replicate this on my Macbook Pro under 11.2.3 Big Sur with Audacity 3.0.2


I have reconfirmed this phenomenon on iMac 27-inch 2020 macOS 10.15.7, Mac mini Late 2012 macOS 10.14.6 and iMac 27-inchi Late 2013.

What does that mean?
Perhaps a couple of screen shots may help to show what you mean.

When I apply the compressor to the upper track, the time shifts in the positive direction.

I can’t reproduce that on Linux.

Is this the compressor that you are using?

Does it still happen if you turn off “Sync Lock”?
Does it still happen if you “Reset configuration” (“Tools” menu)?

If it does still happen, what settings are you using in the compressor effect?

I can reproduce the problem now on W10 - having seen tac2’s last image post (thanks for that tac2). I manage to repeat it with some simpler steps:

  1. Generate 30 second chirp

  2. select from 0-10 seconds

  3. Silence that selection with Ctrl+L

  4. Ctrl+A to select all

  5. Effect>Compressor
    01 Compreesor no negative time.png

  6. Undo to remove the compression

  7. Drag track leftwards with Timeshift tool so 9 seconds are in negative time

  8. Ctrl+A to select all

  9. Effect>Compressor
    02 Compressor 9secs negative time.png
    Note carefully that the waveform is now only 11 seconds log and the 20 it should be


  10. drag waveform right with Timeshift tool so that all the audio is in positive time sating at T=0
    03 Compressor fault.png
    It looks to me as though
    a) the waveform has been pushed rightwards by the 9 seconds with 9 seconds silence added
    b) the waveform has bee truncated on the right by 9 seconds

This could be serious for a user who (for whatever reason) has a large amount of audio in negative time and applies compression to the whole track - as they will lose track data from the far end and that may bot be immediately visible or apparent to them.

The workaround is to
11)use click&drag (or the Selection Toolbar) to select just the portion in positive time ( and NOT Ctrl+A)
12) Effect>Compressor
04 Compressor no selection in negative time.png

Note too that when you have a selection in negative time - the start Time in the Timer toolbar gives no helpful information
05 Compressor issue - unhelpful Start time.png
But this is a different issue

I tried this with several other effects and this does not affect them in the same way.

I plan to log this , but first I will need to test this on my Big Sur Macbook.

@Steve: can you please retest on Linux with these steps to reproduce.

This is what I get at that step:


I get the same results on My Big Sur macOS 11.2.3 Macbook Pro

I’ll be logging this later today.


That is to be expected because time widgets only support positive values. It’s the result of the (frankly, rather dumb) idea that supporting negative time regions was a good thing, when actually it opens a big can of worms. I don’t see this to be a “bug”, but rather a consequence of a series of bad design decisions.

Steve, at Step 8 did you use Ctrl+A (thereby selecting the negative 9 seconds as well as the positive 21 seconds)?
Look carefully at the “timeless” start time in the Selection toolbar.

Your image is what I get if I used click&drag to select just the 21 seconds that are in positive time.


It’s a bug because
a) it only affects Compressor and not the other effects
b) it can result in the loss of data

And it’s a bug of our own making for allowing audio in negative time …


Yes. You can see in my screenshot (highlighting in the timeline) that the selection extends before t=0.

I get the “–h–m-- —s” display whenever the selection starts before t=0.
The time widget has no way of showing negative values.

OK so Ill be logging this as a Mac & Linux bug then 0 does not happen on Linux

This is a regression on 2.4.2 where it works properly - but an improvement on 3.0.0 where

a) On W10 Audacity crashes at Step 9

b) on Mac at Step 9 you get the error mesage

Internal Error>Internal error at wavetrack.cpp line 1374
Please inform the Audacity team at https:/


Logged as P2 Regression Bug #2753 for Win and Mac
Compressor works incorrectly when selected audio is partly in negative time

Good catch tac2 - thanks for the report :slight_smile: :sunglasses:

BTW the workaround is:
Don’t use Cmd+A to make your selection for Compressor - zoom the project to fit the screen and then use Click&Drag to select the audio