About the Spectral Toolbox

The Spectral Toolbox is a suite of analysis-resynthesis programs that locate relevant partials of a sound and allow them to be resynthesized at any specified frequencies. This enables a variety of techniques including spectral mappings (sending all partials of a sound to fixed destinations), spectral morphing continuously interpolating between the partials of a source sound and a destination) and dynamic tonality (a way of organizing the relationship between a family of tunings and a set of related timbres). A complete application called the TransFormSynth concretely demonstrates the methods using either a one-dimensional controller such as a midi keyboard or a two-dimensional control surface (such as a MIDI guitar, a computer keyboard, or the forthcoming Thummer controller).

The Spectral Toolbox is featured in the Computer Music Journal paper Spectral tools for Dynamic Tonality and audio morphing. The paper describes the following sound examples, as well the software available for download below.

Audio examples

Maple Leaf Rag Scot Joplin's famous ragtime piece is used to demonstrate some of the processing techniques

Noisy Leaf Rag Both melody and harmony are removed from the Maple Leaf Rag, leaving only the underlying rhythmic pattern.

multiphonics morphs #1 (type 1) Different kinds of audio morphings are demonstrated by morphing between various clainet multiphonics.

multiphonics morphs #1 (type 2)

multiphonics morphs #2 (type 1)

multiphonics morphs #2 (type 2)

multiphonics morphs #3 (type 1)

multiphonics morphs #3 (type 2)

original gong

harmonic gong with all partials mapped to 65 Hz

65 Hz Rag Maple Leaf Rag with all harmonics mapped to multiples of 65 Hz

Maple-makeharm Maple Leaf Rag mapped to harmonic sound with changing fundamentals

Maple 5-TET Maple Leaf Rag mapped to 5-TET

Make Believe Rag (many different n-TET mappings)

Four versions of clarinet + harmonics:

Legend (24-TET melody only)

Legend (melody morphed into the multiphonics #1)

Legend (melody morphed into the multiphonics #2)

Legend (melody morphed into the multiphonics #3)

Legend (melody morphed into the multiphonics #4)

Legend (Performance)


C to Shining C: This is an early example of Dynamic Tonality. The piece contains only one chord, Cmaj, played throughout, yet a sense of harmonic tension is imparted by a tuning progression and a timbre progression, as follows:

  • Cmaj 19-TET/harmonic -> Cmaj 5-TET/harmonic -> Cmaj 19-TET/consonant -> Cmaj 5-TET/consonant
    • The timbre progresses from a harmonic timbre (with partials following the harmonic series) to a pseudo-harmonic timbre (with partials adjusted to align with the notes of the current tuning) and back again.
    • Twice as rapidly, the tuning progresses (via polyphonic tuning bends), within the syntonic temperament, from an initial tuning in which the tempered perfect fifth (P5) is 695 cents wide (19-tone equal temperament, 19-TET) to a second tuning in which the P5 is 720 cents wide (5-TET), and back again.

The piece is recorded in (or transposed in the recording to) D major, despite its name. As the tuning changes, the pitches of all notes except the tonic change, and the widths of all intervals except the octave change; however, the relationships among the intervals (as defined by the syntonic temperament's period, generator, and comma sequence) remain invariant (i.e., consistent) throughout. This invariance among a temperament's interval relationships is what makes invariant fingering (on an isomorphic keyboard) possible, even while the tuning is changing. In the syntonic temperament, the tempered major third (M3) is as wide as four tempered perfect fifths (P5's) minus two octaves – so the M3's width changes across the tuning progression from

  • 380 cents in 19-TET (P5 = 695), where the Cmaj triad's M3 is very close in width to its just width of 386.3 cents,
  • to 480 cents in 5-TET (P5 = 720), where the Cmaj triad's M3 is close in width to a perfect fourth of 498 cents, making the Cmaj chord sound rather like a Csus4.

Thus, the tuning progression's widening of the Cmaj's M3 from a nearly-just major third in 19-TET to a slightly flat perfect fourth in 5-TET creates harmonic tension, which is relieved by the return to 19-TET. This is an example of Dynamic Tonality's ability to expand the frontiers of tonality by offering new means of creating tension and release, even within a single chord.

Shred, Magic Traveller, Lighthouse: This is a live performance of three pieces: Shred is from 0:00-3:18, Magic Traveller is from 3:18-06:26, and Lighthouse is from 06:26 – end. Performance by Andrew Milne (Thummers), Anthony Prechtl (QWERTY keyboard and oud), Aki Tulikari (drums), at the Music Mind Technology Concert, Jyväskylä University, April 22nd 2008.


First download these installation instructions

You'll need these java classes

plus either the:

Spectral Toolbox for Max/MSP runtime code—use this if you have Max/MSP runtime installed, but not if you also have the full version of Max/MSP.

or the

Spectral Toolbox for Max/MSP (source code)—use this if you have the full version of Max/MSP installed.


Find out about the TransFormSynth

Find out about the Spectral Toolbox

The Spectral Toolbox was designed by William Sethares with the help of Stefan Tiedje, Andrew Milne, and Anthony Prechtl. The Spectral Toolbox and the text on this webpage are released under the GNU General Public License v2.0.

Site design by Anthony Prechtl