This patch implements nonlinear distortion in the resonant ladder
filter. It's based on the differential equations in the Huovilainen '04
DAFx paper, but using matrix exponential to compute the evolution of the
state variables. The implementation is scalar (and calls into sqrtf),
but designed to be implemented in very efficient SIMD.
This patch wires up the LFO to the synth unit, and makes it affect pitch
(control over amplitude is not there yet). It also adds LFO delay to the
base LFO implementation, and there are some other cleanups as well (for
example, not unpacking patch data every note).
LFO speeds, delays, and pitch modulation ranges have been calibrated
against the DX7, but testing hasn't been exhaustive.
Finally implements detune (using an approximation, but better than
nothing). Also minor improvements to note generation, including scaling
output level more accurately, and getting rid of dynamic allocations of
note objects.
On API 17+ (JellyBean MR1), get the buffer size and sample rate from the
platform, and use that, rather than hardcoding the defaults. We're still
using an internal buffer size (N) hardcoded to 64, so the amount of
computation per callback is not as consistent as it would be if that
were more flexible.
More sophisticated note stealing (better than round robin) and also
implementation of sustain (on midi controller 64). This implementation
matches the DX7 precisely.
This change adds a (single) resonant filter to the C++ synth unit, and
wires up both USB MIDI and on-screen controls for cutoff and resonance.
Also fixes a bug in KnobView which caused the knob value to jump around.
Raph Levien