On Apr 4, 2011, at 10:48 PM, Seth Nickell wrote:
2) Anyone have requests for features/api? Its currently simplistic:
- takes a "read FILENAME" message, loads the file, does a test
convolution against pink noise to normalize the gain to something
sane
Is this done within the main Pd audio thread?
The convolution engine has support for doing it either on the calling
thread, or a background thread. I'm thinking of default to a
background thread. That seem like the right move?
Pd has its own scheduling system which is best to stick to as long as
you can so that you can keep the deterministic operation intact. For
convolution, I can't see a reason to use a thread. It adds complexity
and more code to run, but if the CPU is overtaxed by realtime
convolution processing, you are going to get an interruption in the
audio regardless of whether the processing is in a thread or not.
.hc
- caches the last N impulse responses, as the test convolution
takes a little time
- allows setting the cache size with a "cachesize N" message
To make sure I understood this: cachesize is not the size of the
first
partition of the partitioned convolution, but the cache that tries
to avoid
audio dropouts when performing the test convolution?
The convolution engine can swap-in a pre-loaded ('cached') IR in
realtime without glitching... but it means keeping 2x the Impulse
Response data in RAM. To keep the default API simple but useful, I'm
defaulting to caching only the last 5 impulse responses in RAM.
"cachesize N" lets you increase that number.... lets say in a
performance you wanted to use 30 different impulse responses and you
have 2GB of ram... should be nbd.
- disable normalization with "normalize 0" or "normalize 1"
Yes, disabling this could be a good idea! You could also add a
"gain 0-1"
message for manual control.
Its worth noting that impulse responses are usually whack without gain
normalization.... like factors of hundreds to millions off a usable
signal.
Features I'm considering (let me know if they sound useful):
- load from an array instead of from disk (no gain
normalization?)
Very good.
- It wouldn't be hard to enable MxN convolution if that floats
somebody's boat.
I am sure if you come up with a convolution as efficient and
flexible as
jconv by Fons within Pd, then soon a multichannel use and hence
request will
come up fast.
I'd be interested in what flexibility means in this context, it might
give me some good ideas for features to add. Efficiency-wise, last
time I benchmarked its more efficient than jconv, but the difference
is offset by less graceful degradation under CPU load (I convolve in
background threads to preserve realtime in the main thread while
avoiding an irritating patent that's going to expire soon...).
WRT to Pd's audio scheduling... are Pd signal externals held to
realtime or can my dsp call vary the number of cycles it takes by 100%
from call to call? VST seems to do ok with this, but AudioUnits get
scheduled to run at the very last instant they possibly could. If Pd
can have some variance, I can drop the threads and improve the
external's degradation under high CPU load.
thanks for the feedback (also, is the best list for this kind of
feedback?),
-Seth
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