On 2/25/14 2:48 PM, Ross Bencina wrote:
On 26/02/2014 2:25 AM, robert bristow-johnson wrote:
are you trying to do multiple cycles of the sine and then have a
discontinuity as it snaps back in sync with the side-chain waveform? if
so, that doesn't sound very "bandlimited" to me.
As I understand it, the question is now to make such snap-back band
limited.
so that's the same issue with regular saw-sync or square-sync, but with
the sine instead.
The approach that I am familiar with is the "corrective grains"
approach (AKA BLIT/BLEP/BLAMP etc) where you basically run a
granulator that generates grains that cancel the aliasing caused by
the phase discontinuity. The exact grain needed is dependent on the
derivatives of the signal (doable for sine waves). The original paper
for this technique is Eli Brandt (2001), "Hard sync without aliasing",
Proc. ICMC 2001.: http://www.cs.cmu.edu/~eli/L/icmc01/hardsync.html
yup that was the BLIT stuff, i think, so a sawtooth is the integral if
this BandLimited Impulse Train (with a little DC added).
I have not read Vadim's paper so I am not familiar with the alternatives.
you can, pretty cleanly, if you have a lotta memory available to the
oscillator, have a family of curves that would replace the 2 or 4
samples immediately adjacent and both sides of the beginning of the
synced oscillator cycle. you need a family of curves because the of the
different states the sine wave would be in when you begin to "snap" the
phase back. if the curve tables have enough points, you can linearly
interpolate.
if this was a synced saw, you would need only one "snapback" curve
because the only difference, i think, would be just a scaler applied to
curve depending on the state of the saw wave.
exactly what the curve (and siblings) would be, mathematically, is not
something i will spell out. we all get to purvey our own particular
pixie dust (like some of us have for good old-fashioned bandlimited
interpolation between samples that might be burned into a chip like an
AD1890).
--
r b-j r...@audioimagination.com
"Imagination is more important than knowledge."
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