SpectraScore – User Guide

What this does

SpectraScore is a lightweight spectral orchestration tool inspired by IRCAM's Orchidée and Orchidea systems. It analyzes a target sound's acoustic properties (pitch, loudness, timbre, harmonicity) and automatically searches through combinations of orchestral instruments to find the best timbral match. The script extracts fundamental frequency via autocorrelation, measures intensity for dynamic assignment (pp/mf/ff), calculates spectral centroid (brightness) and spread (texture), and analyzes harmonic energy distribution across six frequency bands. Using this spectral fingerprint, it searches through 1 to K instrument combinations (K=2–12), scoring each based on weighted distance between target and combined instrument timbres, with smart heuristics to avoid doubling the same section unless divisi is allowed and to prevent dynamic overshooting. The output is a complete MusicXML score with proper transpositions, clefs, and whole-note durations, where instruments can be voiced in unison, distributed across octaves, arranged as chords, or—most powerfully—assigned to specific harmonics in a spectral orchestration strategy that matches each instrument's natural brightness to reinforce particular overtones of the target sound. The system supports full microtonal tuning with configurable precision (quarter-tones, eighth-tones, or finer), calculating exact cent deviations for each harmonic and encoding them in MusicXML with both <alter> values and <accidental> symbols for compatibility with notation software like bach.score, Finale, or Dorico, making it invaluable for composers exploring spectral orchestration, timbre-matching, computer-assisted composition, or anyone wanting to analyze a sound and receive an instant, musically meaningful orchestral transcription that captures its essence.

Orchestration Theory

SpectraScore implements a simplified version of target-matching orchestration pioneered by IRCAM. The theoretical foundation:

Core Principle

Orchestral instruments have characteristic spectral signatures defined by their centroid (brightness), spread (spectral width), and harmonic structure. By measuring these features in a target sound and comparing them to a database of instrument timbres, we can find instrument combinations that approximate the target.

Analysis Pipeline

1. Pitch Detection: To Pitch (ac)... extracts F0 via autocorrelation
2. Intensity: To Intensity... measures mean dB → dynamic (pp/mf/ff)
3. Harmonicity: To Harmonicity (cc)... extracts HNR (harmonic-to-noise ratio)
4. Spectrum: To Spectrum → centroid (brightness), spread (texture)
5. Band Energy: Six frequency bands (50–10000 Hz) capture energy distribution

Distance Metric

Each instrument combination is scored using weighted Euclidean distance:

score = |centroid_target - centroid_inst| / 2000 
      + |spread_target - spread_inst| / 1000
      + 0.5 × |odd_even_target - odd_even_inst|

Lower scores indicate better matches. The search explores all combinations from K=1 to max_combination_size.

Spectral Mixing

For combinations, spectra are linearly mixed (averaged), and descriptors are recomputed. This approximates acoustic superposition without requiring convolution.

Voicing Strategies

SpectraScore offers four orchestration approaches:

Instrument Database

Twelve orchestral instruments with realistic ranges, transpositions, and timbre statistics for three dynamics:

Brightness values are spectral centroids at ff dynamic. The database includes centroid, spread, and odd/even harmonic ratios for pp, mf, and ff.

Quick start

1. In Praat, select exactly one Sound object (your target sound).
2. Run script… → SpectraScore.praat.
3. Choose instruments to enable (check/uncheck boxes).
4. Set voicing_strategy to Spectral for best results.
5. For microtones: set min_harmonic = 7, microtone_precision = 12.5.
6. Set max_combination_size (2–12 for fuller orchestration).
7. Click OK.
8. The script prints analysis + MusicXML to the Info window.
9. Copy the MusicXML output and save as .musicxml file.
10. Import into Finale, Dorico, or Max/MSP bach.score.

Parameters (form fields)

Outputs

The script prints to the Info window:

• Target Analysis: F0, intensity, HNR, centroid, spread, spectral bands
• Search Progress: Shows combinations tested and scores at each K level
• Best Match: Lists selected instruments with final score
• Voicing Assignments: Shows which harmonic each instrument reinforces, with MIDI note + cent offset
• Microtonal Alter Values: Debug output showing <alter> calculations
• MusicXML Output: Complete MusicXML 3.1 score ready to copy/paste

MusicXML Structure

The generated score includes:

• One part per instrument with proper <part-name>
• Correct clef (<sign>G/F/C</sign>)
• Transposition for B♭/F instruments (<transpose><chromatic>)
• Whole-note duration (<type>whole</type>)
• Dynamic marking (<dynamics><pp/mf/ff/>)
• Microtones: <alter>0.63</alter> (decimal semitones) + <accidental>quarter-flat</accidental>

Microtones in bach.score

To display microtones in Max/MSP bach.score:

1. Set tonedivision to 8 (eighth-tones) before importing MusicXML
2. Use microtone_precision = 12.5 in the script (12.5 cents = 1/8 tone)
3. Set min_harmonic = 7 to force higher harmonics with significant cent deviations
4. Import the MusicXML file into bach.score
5. The <accidental> tags will display as quarter-sharp/flat symbols
6. The <alter> values control playback pitch

Accidental Symbols

The script automatically adds MusicXML accidentals based on cent deviation:

• 12.5–37.5 cents: sharp-up / flat-down (small arrow)
• 37.5–62.5 cents: quarter-sharp / quarter-flat
• 62.5–87.5 cents: three-quarters-sharp / three-quarters-flat