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0 pointsa-dub4y ago0 comments

i'm guessing you're talking about things like og 4 tap biquads and the like.

in the time domain, you're looking at what... for each sample a pointwise multiply for each tap and then a sum, right? i'm guessing for most audio applications at commonly used sample rates, you're rarely going to have more than 24 taps at the very most? (with most only really needed 8 to 16?)

with the fft, unless you're using super exotic multiwindow schemes, you're looking at a pointwise multiply just to do the windowing before the fft. then you're looking at n log n to compute the fft itself, then zeroing or applying an envelope (pointwise multiply), then another n log n back to the frequency domain.

i think with simd you're way faster to just stay in the time domain.

would be interesting to bench for sure though... small ffts and simd may be super fast and not that many instructions.

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TheOtherHobbes4y ago

It's not unusual to use hundreds of taps for a clean linear phase filter with a sharp slope. Discrete convolution reverb would need hundreds of thousands - which is why you use an FFT for that.

a-dubOP4y ago

interesting. just looked at a datasheet for a modern audio dsp and they set aside memory for ~256 coefficients per 48k channel. i guess big filters are a thing.

still, you're looking at applying a window before the fft in most applications. that's a full pointwise multiply before even stepping into the fft (and back).

reverbs have delay lines, right? what does that look like in the spectral domain? some shift of the phases?

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