iPodRocks

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Settings — Harmonic Analysis ​

Harmonic Analysis controls how iPodRocks detects musical key and BPM. This data powers Savant's harmonic ordering and the Library/Savant info banners.

What it does ​

  • Coverage stat — Shows how many tracks have key data vs BPM-only vs none.
  • Extract harmonic data on scan — Read key and BPM from file tags (TKEY, TBPM) during library scan.
  • Analyze with Essentia — Use Essentia.js to detect key/BPM from the audio waveform. Slower but works when tags are missing.
  • Backfill % — When using tag extraction only, percentage of library to process in one backfill run.
  • Analyze % — When using Essentia, percentage of library to analyze per backfill run (genre-sampled).

How it works ​

  • Tag extraction — Reads TKEY and TBPM from ID3/native tags. Fast, but many files lack these tags.
  • Essentia — Decodes audio, runs KeyExtractor and RhythmExtractor2013. More accurate, but CPU-intensive. A single WASM instance is reused to avoid memory leaks.
  • Backfill — Processes tracks that do not yet have key data. Skips already-processed tracks. Run from Settings or the Savant tab.
  • Camelot — Keys are converted to Camelot notation (e.g. 8B) for harmonic mixing. Savant uses this to order tracks.

How to work with it ​

  1. Enable "Extract harmonic data" — Always recommended. Re-scan the library to pick up tags.
  2. Enable "Analyze with Essentia" — When many files lack key tags. Set Analyze % (e.g. 10% per run). Run Backfill from the Savant tab or Settings.
  3. Re-scan — After changing "Extract harmonic data", run a full library scan so new scans use the setting.
  4. Backfill — Run when you have BPM-only or no key data. It only processes tracks that need it; already-done tracks are skipped.
  5. Library/Savant banners — Show coverage and link to Settings when coverage is low.