detect_transients (Tab to Transient, Separate at Transients, Beat Detective)
missed most onsets that weren't the loudest around, and put notes that start
over a ringing note 25-35 ms early, in the previous note's tail. Its
threshold was a share of the loudest flux in the analysed audio, so quiet
hits vanished next to loud ones and the result changed with where the
analysis started. It placed each onset on the first sample reaching a
quarter of the frame's peak, which a ringing note already does.
- Vibrato-suppressed spectral flux: 21 ms windows 5.3 ms apart, log
magnitudes on 24 bands per octave from 30 Hz to 20 kHz, each band compared
with the loudest of its neighbours in the frame before, so vibrato and
chorus don't count. Channels are analysed as the sum of their energies,
so stereo content that cancels in mono still counts.
- A peak must be the highest within 30 ms and exceed the mean flux from
100 ms before to 70 ms after by a fixed amount (2.5 at sensitivity 0.5),
so quiet hits count and the result doesn't depend on where the audio
starts.
- A fast release smears energy between a note's partials, which looks like
a rise. A detection also needs a 3 dB step in its high-passed energy, or
total energy that grows in its frame or the next.
- Each onset goes to the step edge of the high-passed energy (the sample
where the next 3 ms gain most over the 6 ms before), then back to where
the energy crosses the midpoint between the two: 0.3-0.5 ms before
percussive attacks.
On 29 synthetic cases with known onsets (drums with ghost notes; drum-synth
grooves dry and through reverb, compression and limiting; 180 bpm; flams and
claps; legato piano; plucked bass and guitar; strums; 808 kicks; hand drums;
synth bass, leads, pads and staccato notes; string swells; a vibrato pad;
quiet hits over noise and hum; stereo pairs; formant syllables), the
F-measure went from 0.658 to 0.977. It found 1398 onsets instead of 870,
with 5 false ones instead of 315; all 5 are vowels starting after a
consonant. Still missed: hats under a crash, ghost notes under a louder
hit's tail, and slow string swells.
The old offline_meters test bursts stopped dead at -37 dB, an audible click
that now counts as a transient; they ring out instead.
grovebit