From ba74a824658f7f59add288d28006ff48bf46b963 Mon Sep 17 00:00:00 2001 From: Vito Caputo Date: Mon, 3 Feb 2020 00:29:09 -0800 Subject: libs/sig: introduce a signal generator abstraction This adds a small framework of sorts for creating and composing signal generators. Two generators are implemented at this time; sig_ops_sin and sig_ops_mult sig_ops_sin accepts a hz variable and will produce a sine wave of that frequency. sig_ops_mult accepts two sig_t generators and multiplies their outputs Callers may construct their own sig_ops_t ops structs and supply them to sig_new(), but it's expected that libs/sig will grow a collection of commonly used generators which can then be used by simply passing their sig_ops_$foo to sig_new(). See the test code at the bottom of libs/sig/sig.c for some contrived sample usage. Note by composing multiple sig_ops_sin generators with a sig_ops_mult generator, one can already easily construct a synth-like LFO generator. Some obvious todos are to add triangle/sawtooth/square wave generators. More compositional generators may be interesting as well, like additive and subtractive for example. Those will need to implement clipping, as it's expected that the generators *always* stay within unity (0-1). No modules use this yet, but I expect to wire this up to rtv for driving knobs. --- src/libs/sig/ops_sin.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) create mode 100644 src/libs/sig/ops_sin.c (limited to 'src/libs/sig/ops_sin.c') diff --git a/src/libs/sig/ops_sin.c b/src/libs/sig/ops_sin.c new file mode 100644 index 0000000..b228b49 --- /dev/null +++ b/src/libs/sig/ops_sin.c @@ -0,0 +1,49 @@ +#include +#include + +#include "sig.h" + + +typedef struct ops_sin_ctxt_t { + float hz; +} ops_sin_ctxt_t; + + +static size_t ops_sin_size(va_list ap) +{ + return sizeof(ops_sin_ctxt_t); +} + + +static void ops_sin_init(void *context, va_list ap) +{ + ops_sin_ctxt_t *ctxt = context; + + assert(ctxt); + + ctxt->hz = va_arg(ap, double); + assert(ctxt->hz >= .0001f); +} + + +static float ops_sin_output(void *context, unsigned ticks_ms) +{ + ops_sin_ctxt_t *ctxt = context; + float rads_per_ms, rads; + unsigned ms_per_cycle; + + assert(ctxt); + + ms_per_cycle = ctxt->hz * 1000.f; + rads_per_ms = (M_PI * 2.f) * ctxt->hz * .001f; + rads = (float)(ticks_ms % ms_per_cycle) * rads_per_ms; + + return sinf(rads); +} + + +sig_ops_t sig_ops_sin = { + .size = ops_sin_size, + .init = ops_sin_init, + .output = ops_sin_output, +}; -- cgit v1.2.3