Notch Filter Adds Phantom Track Segments At The End Of Tracks

I am processing series of 20-30 ½-hour to 1-hour tracks, and all within one project (multiple files). Each track is different in time length and, because these are sourced from TV shows and movies (ac3 files from video containers) they often have a hum that Notch Filter easily removes.

However, when applying Notch Filter on these projects, Notch Filter will take the longest track time in the project, and then add a silent segment of track, to any shorter tracks, in order to make all tracks equal in time. This silent filler is added to the end of the shorter tracks after all tracks have finished being processed by Notch Filter.

I hesitate to use Truncate Silence because that risks shortening the legitimate track which would introduce lag to the video.

Does anyone know how to stop this odd behavior, or delete this secondary track without individually mouse-selecting the added segments and deleting them manually? Perhaps there are better plugins for notch removal other than the default Notch Filter?

My OS is Win10 Pro and I’m using Audacity 3.6.4

You can’t stop it. It’s a limitation of Nyquist plug-ins. These kind of plug-ins operate on the entire selection - Nyquist sees selected track that are “empty” as “silence”.

You can avoid the problem by selecting one track at a time and processing them one at a time. That would obviously be rather tedious to do manually, but you may be able to automate the process with macros.

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Thanks. After lots of testing, I found that the “Detach at Silences” edit feature will remove these spuriously added track segments with only a few +/- milliseconds being added to the original audio length. The “Truncate Silence” filter is too limited (minimum -80dB threshold) and deletes too much in the original audio.

Well, “Detach at Silences” doesn’t work. The loss of even a handful of milliseconds will cause noticeable lip-sync problems. If anyone else has any idea how to either bypass the problem created by “Notch Filter” or how to delete the superfluous track that is created without the use of a mouse (i.e.; without manual actions), I’d be grateful.

Perhaps you could say more about the use case. It certainly sounds unusual and very specific.

I’m not sure what else to add to the OP, without some coaching. What type of info would you like?

For example:

  • Why do you have 20-30, ½-hour to 1-hour tracks, all within one project?
  • Do the tracks need to be in one project, or have you put them into one project so that you can process them all together and then “Export multiple” to save as separate files?
  • Why do you have so many tracks that all need notch filtering (with the same filter settings)?

These are demuxed ac3 files from ripped DVDs. Once the audio is processed with Audacity, the audio files are muxed with the video files (thus the importance of maintaining track length integrity for lip-sync purposes).

I am compressing and limiting the audio files to raise voices, while compressing laugh tracks, sound effects, music, etc. One season of a TV show, for example, may have 20-40 episodes and all with the same audio characteristics so, I can apply the same settings to all of these files in a single project. In such projects, I may also need to apply “Notch Filter” or “Noise Reduction.”

The reason for “Notch Filter” is because many of these episodes have a small hum which can be noticeable in quiet passages. Of course, as in the OP, once I apply “Notch Filter” to these large projects, that unacceptable (lip-sync issue) phantom segment is added to all tracks that are shorter than the longest track.

Presently, I’m working on a way (not, yet, solved) to automate the removal of these segments via combinations of clip selection (the “Notch Filter”-added phantom) and cursor placements (including the “Nyquist Prompt” issue that you addressed in another of my posts). I use a stand-alone macro program (MacroExpress - similar to autoit) that manipulates all of the various Audacity capabilities (including “Export multiple” to save as separate files) so that I can push a button and walk away since the processing, and other series of steps, can take hours to complete.

That makes sense, but it sounds like an alternative approach will work better.

Rather than putting all of the tracks into one project, you could “batch process” the files using a macro. Your macro would contain a sequence of commands to apply each effect (compression, notch filter, noise reduction, anything else), and ending with an “Export” command. You would then apply the macro to files, selecting all of the ripped files.

The one slightly awkward command is the Noise Reduction effect, because you will need to capture the noise profile manually before you run the macro.

This approach will avoid the problem of the added silence.

Let me give that some more thought. Early on, I had been avoiding this due to the Noise Reduction effect. I do use the Audacity macros to apply the filter combinations, now. As it turns out, though, Noise Reduction isn’t needed as often as I thought it would be. It may be that I could run the single-track projects, as you suggested, and apply noise reduction, to all now-processed files in a single project as a final noise reduction stage. The noise reduction does need to applied as a last step anyway. Good thought.

With some time and effort, I found a solution. It was triggered by your idea of processing the files, one at a time. However, I am now able to do it within a single project. Utilizing the macro manager; Macro Express, I first load the many audio tracks into a single project. I then apply “Notch Filter” to each track, one-by-one, and, once completed, I can apply the Audacity macro containing the compressor, limiter and Noise Reduction to the entire project.

The trick was to find the right filters to avoid adding the phantom tracks, mentioned above. To do this, I first move the focus to the first track using “Move focus to first track”. Then, prior to each cycle, I apply Select - None, which is important toward ensuring that only one track at a time is chosen. Following this, I apply Select-Region-“Track start to end”, which prevents the selection extending beyond the end of the track, in order to prevent the creation of the phantom track. Then, I apply Notch Filter. Once completed, Arrow Down moves the focus to the next track down and the cycle is repeated.

The macro program adds various aspects to ensure timing and cycle ending with the last file in the project, but the key to avoiding the phantom track was to use the sequence outlined in the paragraph, above.

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