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Sound class taxonomy

Every catalog entry has a sound_class field that informs validator thresholds, mastering preset selection, and pipeline routing. There are 7 classes:

synth-pure

Pure mathematical synthesis — binaural beats, isochronic pulses, solfeggio tones, single-frequency drones.

  • What it sounds like: a sine, a square, a binaural beat. Frequency is the entire content; if you change it, the psychoacoustic effect breaks.
  • Validator tuning: disable intent-drift and loosen spectral-anomaly (anything outlier IS an artifact, but CLAP doesn’t understand pure tones).
  • Mastering: studio-binaural-pure ONLY. No EQ, no compression, no reverb.
  • A/B eligibility: yes — the studio chain often adds harmonic warmth that pure synthesis misses.
  • Pipeline preference: DSP only. Never AI-generate.

synth-ambient

Pads, drones, evolving textures — synthesised but not single-frequency.

  • What it sounds like: a warm pad, a slow drone, a synth bed.
  • Validator tuning: loosen intent-drift; standard spectral-anomaly
  • Mastering: studio-pad-ambient or studio-drone-deep (depends on register).
  • A/B eligibility: yes.
  • Pipeline preference: DSP first; ElevenLabs SFX as fallback if DSP feels flat.

cultural-instrument

Singing bowls, gongs, bells, chimes — sounds made by physical objects with complex resonance.

  • What it sounds like: that’s clearly a Tibetan singing bowl.
  • Validator tuning: standard, but per-pattern null for known legitimate tail content.
  • Mastering: studio-bell (preserves transient + tail).
  • A/B eligibility: yes for the mastering chain only.
  • Pipeline preference: Freesound CC0 strongly preferred. DSP attempts (additive synthesis) can land but rarely match a real recording.

animal-specific

Cat purrs, dog breathing, bird songs, owl hoots — animal vocalisations.

  • What it sounds like: that’s clearly a real cat. (Or it’s wrong.)
  • Validator tuning: loose. Animals do unpredictable things.
  • Mastering: light only — preserve realism.
  • A/B eligibility: no.
  • Pipeline preference: Freesound CC0. ElevenLabs SFX as fallback if no good source.

nature-ambient

Rain, wind, streams, fire crackle, ocean waves — field-recording-style environmental textures.

  • What it sounds like: I’m at the actual location.
  • Validator tuning: loose spectral-anomaly (legitimate transients abound).
  • Mastering: light — preserve naturalness.
  • A/B eligibility: no.
  • Pipeline preference: Freesound CC0 strongly preferred.

voice-narration

Affirmations, guided meditations — TTS or recorded human voice.

  • What it sounds like: someone is calmly telling you something.
  • Validator tuning: null intent-drift (CLAP doesn’t understand TTS content); standard others.
  • Mastering: voice-specific chain (hi-pass 80 Hz, sibilance EQ, multi-band, LUFS -20).
  • A/B eligibility: no.
  • Pipeline preference: tts-affirmations pipeline only.

mechanical-ambient

Train rumble, plane white noise, household appliances — mechanical sources that produce ambient texture.

  • What it sounds like: I’m in a moving vehicle / near an appliance.
  • Validator tuning: standard.
  • Mastering: studio-modular or studio-drone-deep work well.
  • A/B eligibility: yes.
  • Pipeline preference: Freesound CC0 or ElevenLabs SFX.

Setting sound_class on a new track

The classify_sound_class.py --apply script (in tools/curate/) uses Gemini Flash to suggest a sound_class for any catalog entry without one. Re-run it after every catalog rebuild because catalog.py overwrites the field.