Time conversion from 'time_signature' and BPM from an Ableton Live 11 MIDI file using python-mido

Question

I have exported a MIDI file from Ableton Live 11 and I would like to extract the variation of the mod wheel in the form of a two-columns table with values and corresponding timestamp in seconds.

For this I have written a Python script using mido to parse the MIDI file. As in this file, there is no 'set_tempo' MetaMessage I provided the BPM value as a parameter to my script. Using the 'time_signature' MetaMessage, I was thinking to convert MIDI time into seconds using the clocks_per_click value. If I got it right, clocks_per_click is the number of MIDI clock ticks per quarter of note. Therefore, my MIDI time to second conversion should be:

# number of seconds in a beat
beat_seconds = 60 / bpm

# number of seconds in a quarter note
quarter_note_seconds = beat_seconds / 4 

# number of seconds in a MIDI clock tick
tick_seconds = quarter_note_seconds / clocks_per_click

# MIDI time to second conversion
seconds = time * tick_seconds

The issue is that the MIDI file from Ableton display 36 clocks_per_click, though it doesn't give me the correct result. The correct result is obtained when clocks_per_click is set to 24.

Here is the MIDI file I am referring to: modramp.zip It is a linear increase of the mod wheel from 0 to 255 during the first beat. The MIDI last one measure.

I would really appreciate if you can explain me why the clocks_per_click seems not to correspond to the time displayed in the messages there and if there would be another way to convert this time value without using the 'set_tempo' MetaMessage, which is missing.

Thank you in advance,

Joel

Answer 1

According to the Ableton Live docs the MIDI export resolution is 96 ppq.

Using Mido I can convert ticks to seconds using the following:

import mido

ticks_per_beat = 96
bpm = 118

ticks = 2688

tempo = mido.bpm2tempo(bpm)
seconds = mido.tick2second(ticks, ticks_per_beat, tempo)

Aside for OP's specific case: It says "which means a 16th note can be divided into 24 steps" so that might be where your 24 number came in. With common time (4/4) a quarter note is the same as one beat, so your quarter_note_seconds should be the same as beat_seconds. Dividing it by 4 would give you sixteenth_note_seconds.