convolution necessarily involves latency, so you cannot directly
process incoming buffers of arbitrary sizes and expect to produce
outgoing buffers of the required size.
What you should do is pick a fixed buffer size which works well with
your number of taps+coefficients and the resulting tail. Then feed
your buffer from the incoming frames, run your convolution, and use
the results to fill the output frames. It seems like you could have
a very small latency with only 10 coefficients and taps, even though
the Process function will be dealing with larger buffers. However,
you cannot directly process things without an indirect step involving
latency.
By the way, your simple code shows a 'delay' buffer on the stack
which would be allocated and deallocated on every Process call. You
cannot expect this to work well. You should allocate such buffers in
your initialize method and make them part of the AU object. latency
basically means that the output samples are delayed in time compared
to the input samples. You must have storage which is not deallocated
between Process() calls in order for this to work.
Brian Willoughby
Sound Consulting
On Jun 23, 2009, at 06:13, Salvator|TriTone Digital wrote:
I'm writing a simple convolution plugin, and face a problem with the
convolution 'tail' beyond buffer size.
Actually the convolution take place fine within the buffer size
boundaries, but at each end of buffer, the tail of convolution is
either truncated, or feedingback.
memcpy(delay, delay+inFramesToProcess, sizeof(float) *
numTaps-1); // i.e. save content by moving samples at beginning
memcpy(delay+numTaps-1, inSourceP, sizeof(float) *
inFramesToProcess); // i.e. fill the last samples with input signal
vDSP_conv(delay,1,coefficients+numTaps-1,-1,inDestP,
1,inFramesToProcess,numTaps);// convolve "delay" with "coefficient" &
output into inDestP
}
Any hints on how making the convolution preserving the samples that
would be beyond "inFramesToProcess" ?
I also tried a circular buffer implementation, but face the exact
same problem so I posted this one as it's simpler to read.
Thanks !
Salvator
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