[sdiy] IR Reverb

Eric Brombaugh ebrombaugh1 at cox.net
Fri Feb 16 19:11:32 CET 2018

Yes - a brute force requires 100k MACs / sample.

An FFT approach reduces the the total number of multiply / add 
operations required to do a convolution due to the optimization of the 
"fast" algorithm. FFTs reduce the N^2 operations of a DFT to N*log(N), 
so the larger the transform you can get by with, the more advantage 
you'll see. The downside is that FFTs introduce a lot of latency, so to 
get around this transform-based convolution engines will typically 
subdivide the process into a small & fast FIR to handle the early 
results, followed by gradually larger and larger FFTs to handle the 
later results.


On 02/16/2018 10:53 AM, Tim Ressel wrote:
> Thanks for all the replies!  So the concept sounds simple enough. I get 
> the sense the issue is going to be processing time. Am I wrong, or would 
> a brute-force approach to a 2-second reverb time require 100K MAC cycles 
> per sample? I found some open-source packages that use FFTs to do this. 
> I was under the impression FFTs would be less fast than other methods.
> Ever get the feeling you're opening Pandora's Box only to find a can of 
> worms inside?

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