Re: [SoX-users] Convolution, channel-selectiveness of effects and spectrograms

[Martin G. <mar...@gm...>]

On Fri, 28 Nov 2025 at 20:18, Sergei Steshenko <ser...@ya...> wrote:
> Regardless of particular FFT package, and regardless of the fact
> that SoX works on 32 bit FP audio data, convolutions should rather be
> performed using 64 bit FP data. If necessary I'll explain why - the
> hint: compare values of cos(0) and cos(2 * pi / N) where N number of
> points in FFT.

I don't understand the why (I'm a good code monkey but not so hot in
analogue math)
but I'll remember that, so thanks for mentioning it.
Does the same go for FFTs used for the spectrograms? I'd assumed that
25-bit floats
would lose nothing of significance there and that a 40% speedup might
be possible;
I'll assume that what you say applies to any effect that resynthesizes
audio from FFTs.

I notice that the PFFFT page says it only does single-precision so I assume that
excludes using it for convolutions?

    M