Numerical Label Track

I have need to assign varying numeric values to specific times over the course of an audio track. I can accomplish this using a Label Track and just type in the numbers in the label’s text field. A much nicer solution would be to have a curve that I can edit directly, exactly the same way that the Time Track editor works.

I attempted to use Time Tracks for this, but I am limited to just one per Audacity project, and I can’t seem to find a way to disable it’s effect on playback (I just want to use it for label/annotation purposes).

Question – does a plugin exist that delivers the functionality I’m after here? If not, does the plugin API support creating custom track types, such that I might create this plugin myself?


Please describe in a bit more detail, and give some background to what you are doing. What are the numbers for? How do you intend to use them? …

The best way I can describe this is that it is a variation of a Label Track, but without the tempo-modifying behavior. Instead of accepting free-form text for label values, it takes numerical values and provides an interpolated curve with draggable curve points (just like Time Tracks).

My use case is this – I need to annotate spoken voice tracks with numerical values for emotion and sentiment. These values change over the course of each track, I’d like to just define a series of key points on the curve at specific timestamps and be shown an interpolated curve rendered in the track body. The track data (just curve points, not interpolated values) would need to show up in the .aup xml file for export purposes, just as it already does with Label Tracks.

The Time Track interface already does all of this, except that I can only have one, and that it will govern playback speed if enabled. Basically I want to add any number of Time-Track style label tracks, with no functionality beyond just the ability to add curve points and access them in the underlying data file.

You can’t get exactly what you are asking for unless you are a highly skilled C++ programmer and modify the core Audacity code to create your own custom version of Audacity with a new track type. Plug-ins are not able to create new track types.

There are a couple of options available to you.

The feature in Audacity that is designed for annotating, is the Label Track. This allows you to enter arbitrary text (or numbers) at any time.

  • Audacity supports multiple label tracks (as many as you like).
  • Labels can be created very quickly and easily. There is an option that allows labels to be created just by typing into a label track (see “Type to create a label” on this page:
  • Label tracks can be imported / exported.

The one feature that label tracks don’t have, is they don’t show an interpolated line.

Another option is that you could create an audio track with a very low sample rate. The lowest supported sample rate is one sample per second.
Note that if you do this, the track must be muted when you play, otherwise it will be mixed with the audio and may cause very bad distortion. You can then “draw” the waveform with the “Draw” tool (
Here is an example showing 30 seconds with a muted track that has one sample per second: