The Little Modulator

The Little Modulator is a synthesizer instrument modeled on Yamaha’s famous X-series FM synthesizers. It is implemented as a set of Scheme libraries, with driver programs for performance.

This is a work in progress. The implementation is still quite rough. Bug reports and suggestions — especially on the finer points of synthesis implementation — are welcome.

Source

Tarball (FTP).

At the moment I am working on TLM with Gauche. The implementation will need some adjustment to run under other R⁷RS Schemes.

Features

• Sound synthesis using arbitrary (but currently acyclic) graphs of frequency-modulated oscillators for tone production. (Implemented.)

• Per-oscillator customizable envelope generators. (Implemented.)

• Arbitrary pitch specification by frequency and frequency ratio. No artificial restriction to MIDI-note pitches (i.e. to twelve-tone equal temperament). (Implemented, at least internally.)

• MUSIC V / Csound–style score input for ahead-of-time synthesis. (Implemented.)

• Realtime performance under MIDI control. (TODO.)

Dependencies

TLM is currently written in R7RS Scheme with a few additional dependencies:

• SRFI 1
• SRFI 27
• SRFI 133
• SRFI 196

• The R⁶RS bytevector library (AKA (scheme bytevector)) or the equivalent.

Ahead-of-time Example

The following uses an electric-organ-like instrument (described by Chowning & Bristow in FM Theory & Applications (1986), p. 101) to play a five-note scale (Ptolemy’s diatonic) to the file scale.s16. The format is currently raw 16-bit PCM.

(import (scheme base)
        (scheme file)
        (tlm envelopes)
        (tlm output)
        (tlm score)
        (tlm signal-graphs)
        )

(define my-synth
  (let* ((env0 (make-env 99 150.0 95 45.0 99 0.0))
         (carrier-env (env-scale-levels 20 env0))
         (osc0 (make-osc #f (make-env-generator carrier-env) 1.0))
         (osc1 (make-osc 1.0 (make-env-generator env0) #f))
         (osc2 (make-osc #f (make-env-generator carrier-env) 1.288))
         (osc3 (make-osc 2.0 (make-env-generator env0) #f))
         (osc4 (make-osc #f (make-env-generator carrier-env) 2.042))
         (osc5 (make-osc 3.0 (make-env-generator env0) #f))
         (ov (vector osc0 osc1 osc2 osc3 osc4 osc5)))
    (make-instrument ov '((0) (1 0)
                          (2) (3 2)
                          (4) (5 4)))))

(define my-score
  (list (make-note 0 3 400 64)
        (make-note 4 3 450 64)
        (make-note 8 3 500 64)
        (make-note 12 3 533.333 64)
        (make-note 16 6 600 64)))

(call-with-port
 (open-binary-output-file "scale.s16")
 (lambda (port)
   (play-score port my-synth my-score)))

License

EUPL v1.2 or later.