more detailed information about "duration"

[Schran4er]

Thank you for your work.

Do you mind helping me out with a little bit more information about the "mean_duration" parameter for the expert description?
The only detailed information about duration that I can find in the paper is: "Mean duration is quantized to 32 logarithmically spaced intervals in [0, 128] positions (12 positions per quarter note)."
If I understand this correctly, this would imply that a duration value of 1 is equal to a note being played for 1/12 quarter notes, whereas a duration value of 32 would mean that it is played for 128/12 quarter notes. However, looking at the generated results from the example descriptions, this doesn't seem to be the case.

Kind regards, and thank you in advance!

[dvruette]

Absolutely! Here we're talking about the mean duration, which is computed as follows (in pseudocode):

# 1 position == 1/12 quarter note
mesh = np.logspace(0, 7, 32+1, base=2) # log space between 1 and 128 positions (~2.5 bars)

mean_durations = []
for bar in bars:
  mean_duration = mean(duration_in_positions(note)) for note in bar.notes)
  mean_duration = quantize_to_mesh(mean_duration, mesh)
  mean_durations.append(mean_duration)

Note that the mean duration is only used for the description and does not correspond 1:1 with the duration indices for notes. In case you're referring to note durations: In the REMI+ representation, note durations are actually quantized to a different mesh, which is chosen in a way to have a high resolution for shorter notes and a lower resolution for longer notes (see constants.py for the exact mesh).

I hope this helps, lmk if you still have questions.

[Schran4er]

Thank you very much for the quick response, this already helps me a lot!

Now, just out of curiousity, if "mean duration does not correspond 1:1 with the duration indices for notes": how does it correspond then? Or are you referring to the quantization to the different mesh in REMI+?

[dvruette]

Yes, exactly, I’m referring to the fact that a different mesh is used for quantizing mean durations vs. note durations. To get actual durations from REMI+/description tokens, you’d have to first de-quantize them by indexing the respective mesh.

[Schran4er]

Alright, thx again! I'll let you know if I have any more questions.