RSound: An Adequate Sound Engine for Racket

A note about volume: be careful not to damage your hearing, please. To take a simple example, the sine-wave function generates a sine wave with amplitude 1.0. That translates into the loudest possible sine wave that can be represented. So please set your volume low, and be careful with the headphones. Maybe there should be a parameter that controls the clipping volume. Hmm.

1 Sound Control

These procedures start and stop playing sounds and loops.

2 Sound I/O

These procedures read and write rsounds from/to disk.

The RSound library reads and writes WAV files only; this means fewer FFI dependencies (the reading & writing is done in racket), and works on all platforms.

It currently has lots of restrictions (it insists on 16-bit PCM encoding, for instance), but deals with a number of common bizarre conventions that certain WAV files have (PAD chunks, extra blank bytes at the end of the fmt chunk, etc.), and tries to fail relatively gracefully on files it can’t handle.

Reading in a large sound can result in a very large value (~10 Megabytes per minute); for larger sounds, consider reading in only a part of the file, using rsound-read/clip.

It currently has lots of restrictions (it insists on 16-bit PCM encoding, for instance), but deals with a number of common bizarre conventions that certain WAV files have (PAD chunks, extra blank bytes at the end of the fmt chunk, etc.), and tries to fail relatively gracefully on files it can’t handle.

The file must be encoded as a WAV file readable with rsound-read.

The file must be encoded as a WAV file readable with rsound-read.

3 Rsound Manipulation

These procedures allow the creation, analysis, and manipulation of rsounds.

So, suppose we have two rsounds: one called ’a’, of length 20000, and one called ’b’, of length 10000. Evaluating

(rsound-overlay* (list (list a 5000)

(list b 0)

(list b 11000)))

... would produce a sound of 21000 frames, where each instance of ’b’ overlaps with the central instance of ’a’.

4 Signals

A signal is a function mapping a frame number to a real number in the range -1.0 to 1.0. There are several built-in functions that produce signals.

In order to listen to them, you’ll need to transform them into rsounds:

Here’s an example of using it:

(define samplerate 44100)

(define sr/inv (/ 1 samplerate))

(define (sig1 t)

(* 0.1 (sin (* t 560 twopi sr/inv))))

(define r (fun->mono-rsound (* samplerate 4) samplerate sig1))

(rsound-play r)

Alternatively, we could use sine-wave to achieve the same result:

(define samplerate 44100)

(define r (fun->mono-rsound (* samplerate 4) samplerate (scale 0.1 (sine-wave 560 samplerate))))

(rsound-play r)

So, for instance, if we defined the function flatline as

(define (flatline t l)

l)

... then (signal flatline 0.4) would produce the same result as (dc-signal 0.4).

There are also a number of functions that combine existing signals, called "signal combinators":

We can turn an rsound back into a signal, using rsound->signal:

Where should these go?

Finally, here’s a predicate. This could be a full-on contract, but I’m afraid of the overhead.

5 Visualizing Rsounds

(require (planet clements/rsound/draw))

6 RSound Utilities

So, for instance,

  (fir-filter (list (list 13 0.4) (list 4 0.1)))

...would produce a filter that added the current frame to 4/10 of the input frame 13 frames ago and 1/10 of the input frame 4 frames ago.

So, for instance,

  (iir-filter (list (list 13 0.4) (list 4 0.1)))

...would produce a filter that added the current frame to 4/10 of the output frame 13 frames ago and 1/10 of the output frame 4 frames ago.

not-yet-documented: (provide twopi make-tone make-squaretone ding make-ding split-in-4 times vectors->rsound echo1 fft-complex-forward fft-complex-inverse)

7 Reporting Bugs

For Heaven’s sake, report lots of bugs!