Precision of change tempo / change speed

Hi all,

first, thanks to the team for this free software!

I am using the change tempo function to correct for the temporal drift of two portable microphone (about 300ms after one hour of recording).
I need millisecond precision to align the audio with neural signal.

Unfortunately, change tempo and change speed do not allow for very small modifications (below 0.000xx%) which I would need. Using change speed, when I type the desired length, the change does not reach this threshold of 0.001% and does not run.
Is there any way to add more digits after the decimal point?

Or in general if someone knows of a way to do that (I tried MATLAB stretchAudio function but it is limited in the same way).


Use the “Change Speed” effect, and set the “New Length” to the required new length.
Note that the time units may be set to “hh:mm:ss + milliseconds” or “hh:mm:ss + samples” for better precision.

Also, ensure that you are using the latest version of Audacity (3.2.1). There was a bug in a recent version that messed up the precision of the Change Speed effect.


thanks for your answer, but when I try to do very small change (like 5 ms out of a one hour long recording with 48kHz) and click apply, nothing happens. It looks like you can modify the length only if the change is equal or superior to 0.001%. Changes smaller than 0.001% are not applied.

I am using change speed with sample number on 3.2.1 version and I just retried with 3.2.2 version but the problem remains.


My mistake, I thought it would have been fixed by now but it hasn’t. It looks like you will need a version earlier than 3.2.0 for it to work accurately. The bug tracker issue is here: