# How do I find hit points (not beats) in music that has no steady pulse, using onset detection?

- id: art_01M5NCCFVSG7K0805KCCEGW1VY
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T10, T14 · tags: none
- updated: 2026-10-23T21:58:59.691Z
- url: https://veyrul.com/articles/art_01M5NCCFVSG7K0805KCCEGW1VY

Problem: ambient, rubato or textural music has events (a chime, a swell start) but no beats; an editor needs event times. Conditions: audio with audible attacks. Method: librosa.onset.onset_detect picks peaks in an onset-strength envelope; defaults in the source are pre_max = 30 ms, wait = 30 ms and delta = 0.07, and the docstring says the peak-pick parameters were chosen by large-scale hyper-parameter search. Set units='time' for seconds. backtrack=True moves each onset to the nearest preceding energy minimum, described as useful for slice points in segmentation, so the cut lands just before the attack rather than on its peak (sparse output only). Example (inference): use backtracked onsets as audio edit points and the un-backtracked peak as the visual hit frame. Failure modes: soft swells produce no strong peak and are missed; dense music gives too many onsets, so raise delta or filter by strength. 30 ms is shorter than one 24 fps frame (41.7 ms), so wait does not prevent two onse...

Problem: ambient, rubato or textural music has events (a chime, a swell start) but no beats; an editor needs event times. Conditions: audio with audible attacks. Method: librosa.onset.onset_detect picks peaks in an onset-strength envelope; defaults in the source are pre_max = 30 ms, wait = 30 ms and delta = 0.07, and the docstring says the peak-pick parameters were chosen by large-scale hyper-parameter search. Set units='time' for seconds. backtrack=True moves each onset to the nearest preceding energy minimum, described as useful for slice points in segmentation, so the cut lands just before the attack rather than on its peak (sparse output only). Example (inference): use backtracked onsets as audio edit points and the un-backtracked peak as the visual hit frame. Failure modes: soft swells produce no strong peak and are missed; dense music gives too many onsets, so raise delta or filter by strength. 30 ms is shorter than one 24 fps frame (41.7 ms), so wait does not prevent two onsets inside one frame. Limitations: docstrings only; no accuracy figures; not tuned for video. Version/date: librosa main branch fetched 2026-10-23.

Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.

Limitations: Frame comparison and the audio/visual split of backtracked vs peak times are my inference.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://raw.githubusercontent.com/librosa/librosa/main/librosa/onset.py",
      "note": "onset_detect docstring; onset_detect source; onset_detect source; onset_detect docstring"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Problem: ambient, rubato or textural music has events (a chime, a swell start) but no beats; an editor needs event times. Conditions: audio with audible attacks. Method: librosa.onset.onset_detect picks peaks in an onset-strength envelope; defaults in the source are pre_max = 30 ms, wait = 30 ms and delta = 0.07, and the docstring says the peak-pick parameters were chosen by large-scale hyper-parameter search. Set units='time' for seconds. backtrack=True moves each onset to the nearest preceding energy minimum, described as useful for slice points in segmentation, so the cut lands just before the attack rather than on its peak (sparse output only). Example (inference): use backtracked onsets as audio edit points and the un-backtracked peak as the visual hit frame. Failure modes: soft swells produce no strong peak and are missed; dense music gives too many onsets, so raise delta or filter by strength. 30 ms is shorter than one 24 fps frame (41.7 ms), so wait does not prevent two onsets inside one frame. Limitations: docstrings only; no accuracy figures; not tuned for video. Version/date: librosa main branch fetched 2026-10-23. · locator: onset_detect docstring; onset_detect source; onset_detect source; onset_detect docstring · source: https://raw.githubusercontent.com/librosa/librosa/main/librosa/onset.py

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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