Pitch-Class Spectral Gravity — Tonal Spectral Attraction

What this does

Pitch-Class Spectral Gravity turns a selected pitch collection into a periodic gain field on the log-frequency axis. Every spectral frequency is evaluated by its distance from the nearest member of the collection. Frequencies close to a target pitch class are retained or boosted; frequencies farther away are progressively attenuated.

Key Features:

• Entirely native Praat — no Python, external executables, plugins, or libraries.
• Continuous spectral gravity — smooth pitch-class attraction on a log-frequency axis.
• Optional quantised field — a stepped, harder tuned-grid colour.
• 10 pitch collections — major, minor, harmonic minor, whole-tone, octatonic, pentatonic, chromatic, and custom.
• 5 creative presets — from gentle colouring to a radical resonant grid.
• Mono and stereo — stereo channels are processed independently and recombined.
• Dry/Wet blending — interpolate between the source and the transformed spectrum.
• Explanatory Praat Picture visualisation — pitch-class field, applied gain curve, and input/output spectrum.

Quick start

1. Select exactly one Sound object in Praat.
2. Run Pitch_Class_Spectral_Gravity.praat.
3. Choose a Root and Collection.
4. Start with Preset = Tonal field.
5. Keep Field shape = Continuous for the smooth default behaviour.
6. Use Attraction width to decide how narrowly the spectrum gathers around the target pitch classes.
7. Use Dry/Wet to blend the transformed result with the original.

How it works

1. A periodic field on the log-frequency axis

The selected Sound is converted to a Praat Spectrum. Instead of constructing many band-pass Sound objects, the script builds one gain curve on a dense logarithmic grid and applies it to the spectrum with a lookup for every FFT bin.

s is a MIDI-like semitone position and pc is its continuous pitch-class position around the octave. In Continuous mode the position is not snapped to a note.

2. Distance to the nearest collection member

For each spectral position, the script finds the shortest circular distance d, in semitones, to the nearest active pitch class.

Attraction width is the Gaussian width sigma. A wide value creates broad harmonic colouring; a narrow value leaves only a tight neighbourhood around the selected pitch classes.

3. Complex-spectrum weighting

The same scalar gain is applied to both real and imaginary components of each FFT bin. The operation therefore changes magnitude without deliberately rotating the original spectral phase. The processed spectrum is then transformed back to Sound and mixed with the dry source.

Pitch collections

The chosen Root transposes the selected pitch-class pattern. Custom mode accepts pitch classes as numbers from 0 to 11.

5 Presets

Field shapes

Controls

Advanced settings

Visualisation

When Draw visualization is enabled, the script produces a Praat Picture display with three complementary views:

Technical behavior

• Processes one selected Sound and never modifies the original.
• Uses one whole-sound FFT / inverse-FFT pass per channel.
• Builds the log-frequency gain field once as a Matrix and performs a lookup for each spectral bin.
• Applies identical gain to real and imaginary spectrum components, preserving each bin's original phase angle during weighting.
• Stereo channels are processed independently with the same tonal field and then recombined.
• The selected analysis range is clamped safely to Nyquist.
• The Info window reports the gain range actually measured from the generated curve, rather than estimating it only from nominal pitch-class distances.
• With normalization off, Dry/Wet = 0% is not silently peak-corrected; peaks above 1.0 are reported instead.

Limitations

• Static field: the transform is applied to the entire Sound at once. It does not follow changing notes or trajectories through time.
• Phase preservation is not transient preservation: applying the same gain to real and imaginary components avoids intentional phase rotation, but sufficiently narrow spectral filtering can still ring in time.
• Radical settings intentionally thin the spectrum: very narrow Attraction width plus strong attenuation behaves more like a resonant comb than gentle tonal colouring.
• No spectral transport: non-target energy is attenuated; it is not physically moved into the nearest target band.

Outputs

The script creates a new Sound named:

<original-name>_PCGravity

The output preserves the source sample rate, duration, and channel count. The original Sound remains unchanged.

Applications

Tonalise noisy or inharmonic material

Use case: breath, bow noise, cymbal resonance, metallic scraping, field recordings, or percussion acquire a scale-related spectral bias without being converted into ordinary pitched notes.

Impose harmonic identity without F0 tracking

Use case: multiphonics, complex instrumental sounds, or mixed pitched/unpitched textures can be drawn toward a major, minor, octatonic, whole-tone, pentatonic, or custom field.

12-TET spectral gravity

Use case: choose Chromatic to pull between-note or inharmonic energy toward the 12-tone equal-tempered grid without imposing a key.

Resonant spectral grid

Use case: the Radical preset or Quantised grid can turn the collection into a deliberately narrow spectral scaffold, producing more extreme colour and possible ringing.