Limit on selected audio for filter functions

There appears to be a selection size limit for the low pass, high pass, and notch filter functions. I convert vinyl albums for my friends and have found that the filter functions do not work if the size of the selected audio is greater than 20 minutes (approximate). If the audio selection is over this limit, the functions appear to work normally (no errors) but no modifications are made to the audio. The functions work extremely well as long as the size of the selected audio is below this 20 minute limit. Is this a known limit that simply isn’t documented or is it a bug?

  1. Which version of Audacity? (look in “Help > About Audacity” for the exact version number)
  2. Windows, Mac or Linux?
  3. What is the track’s sample rate? (It is shown in the panel on the left hand end of the track)
  4. What is the Project’s sample rate? (In previous versions of Audacity this was displayed in the lower left corner of the main Audacity window. In Audacity 3.3.0 click on “Audio Setup button > Audio Settings”)

I’m not having that problem…

I opened a concert file, a little more than an hour long. (Stereo 48kHz)

I applied a low-pass filter with a -6dB per octave slope. It completed in a little more than 1 minute.

Then I applied a high pass filter with a -36dB per octave slope. I assumed the sharper filter would take longer but it was a little too fast to time and it took maybe 10 seconds.

Just for information: The filter slope should have little if any affect on the processing speed with these plugins.


  • Operation system is Linux Mint 21.1, kernel 5.19.0-41
  • Audacity version is 2.4.2 which is the latest version available in Linux Mint.
  • Sample rate of the project and track is 192 KHz.

I just completed a recording of an entire album at 96 KHz and the filter functions work normally when the entire project is selected (39 minutes). Obviously, the issue I’m seeing is related to the higher sample rate.

FYI: I have been using Linux since the 1.x versions of the kernel, so I’m not unaware of O/S related issues.

I’m running 3.3.0 on Windows 10 64-bit.

I still haven’t duplicated the problem, so maybe it’s only the Linux version or maybe something with your computer…

I up-sampled to 384kHz and exported as FLAC (too big for a WAV file) just to make sure I was working with 384kHz data. (It took several minutes to export and re-open.)

I ran a high-pass filter on the full 105 minutes and after about 8 minutes the whole file was done.

I’d expect that processing 39 minutes of audio at 192 kHz sample rate to be slow because of the amount of data.
Audacity works in 32-bit float format, so that is 4 bytes per sample, and 192 kHz sample rate means 192000 samples per second, so that is 192000×4×60×39 = 1797120000 bytes per channel, or about 1.8 GB of data (double that for a stereo track).

Keep in mind that Audacity retains an Undo history, so for a 39 minute stereo track you will be increasing the project size by around 3.6 GB each time you process the track.

Is it possible that you are running out of disk space on the drive where the project resides?


System resources are not a problem. I have 170GB of SSD storage dedicated to my audio work (audacity tmp and project files are here), 32 GB of system RAM tied to a Ryzen 3800X 8 core processor. Normal disk storage is approxiamately 6TB of which a little more than half is available. Also, there are no errors in the system logs.

I think we may have a bit of a misunderstanding on the time issue. The 39 minutes is the length of the track in audacity, not the length of time needed to execute the command. The high pass filter command executes in 11 seconds for the 39 minute track recorded at 96K.

It’s odd to me that effects like click removal, normalize, and noise removal all work as expected but the filter effects do not, even though the target audio track is the same. Another odd thing is the lack of an error indication, the commands execute but the audio is not modified. Do you know if audacity tries to access any part of the host file system other than the defined tmp directory and the project directory?

I don’t have an explanation but I do have a fix. I downloaded the AppImage of the 3.3 version from the Audacity website. The problem does not exist in the AppImage 3.3 version that I downloaded. Either there is a bug in the older versions of audacity or there is a bug in the Ubuntu build process of audacity, pick you poison. If I get extremely motivated I will build audacity from source code but for now the AppImage is good enouogh to finish my current project.

The other effects that you mention are built-in effects, written in C++. The filters are Nyquist plug-ins.

My guess is that it’s a build problem, but if I get time I’ll try Ubuntu’s build and see if I can reproduce the issue there.

I’ve checked it out and yes there was a bug in Audacity 2.4.2 that caused the Nyquist filters to fail. I was able to reproduce it with a 1 hour, 192 kHz stereo track. The bug was fixed a couple of years ago, probably when the Nyquist library was updated.

I suppose that answers all questions. Thanks for the info and quick response.

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