Not enough digit precision for the "Change Speed" effect

I’ve recorded a long track (~1h), along with some video footage. The video does not sync up with the audio, most likely because of tiny clock differences between the recording devices.

We need to change the speed of the audio track, but unfortunately the “Change Speed” effect dialog allows to enter the percentage change only with 3 decimal digits of precision. In our case -0.016 is not enough, -0.018 is too much, but -0.017 is not quite there.

Is it possible to enable higher precision in this dialog, or should I create a bug in the tracker?

I’m on Manjaro (Arch), with Linux 5.8.18, Audacity 2.4.1. I’ve installed Audacity from my distribution’s repository

For maximum precision, use the “New Length” setting.

Although it might help with a single modification, we’re recording a new ~1h material every week, and we need to change the length by precisely the same ration each time. Calculating the desired duration for each recording manually each time is far from optimal. More decimal precision would mean that we just have to remember the number to enter and that’s it

As with other controls in Audacity, the percentage change is calculated to more than 10 decimal places precision, but obviously it would be ridiculous to display so many decimal places in every control.

A simple way to access the full precision of the Change Speed effect is to create a Macro containing the Change Speed command.

  1. To obtain the exact amount of stretch required, use the Change Speed effect and set the amount of stretch using the “New Length” setting.
  2. Apply the effect and check that it is correct.
  3. “Ctrl + Z” to Undo the effect
  4. “Tools Menu > Macros”
  5. Add a “New” macro and give it a meaningful name.
  6. Add the command “Change Speed” to the macro - ensure that the settings are identical to what you used in step 1.
  7. Click the “OK” button.

To run the Macro:
"Tools menu > Apply Macro > name-of-macro

Optional: Add a keyboard shortcut to run the Macro (see:

Interesting, will test that out.

I was trying to do kind of a similar thing, by creating a “preset”, exporting it to a file, changing the percentage value within file, and importing it back. But unfortunately it just rounded what I’ve entered to the file to the regular digit precision.

A preset will also work, but the displayed “Percent Change” will still only show 3 decimal places, and you have to be careful not to adjust anything after selecting the preset. The Macro approach has the advantage that it is applied immediately without opening the effect interface, so the exact setting is fixed in the Macro (and you can create a shortcut).