However, what worries me is that if I run a Pd vanilla patch on
different Pd versions (i386 or amd64) with the same floating point
precision, I expect the same results.
Generally, you can't really expect that. Even without -ffast-math,
different CPU architectures or instruction sets will give slightly
different results (unless you jump through various hoops).
Here's an interesting article by a game developer:
https://gafferongames.com/post/floating_point_determinism/
Usually, these errors are very small, but with (suboptimal) recursive
algorithms they can get amplified significantly. Your patch is a very
striking demonstration of the problems with the direct 2 form of the
biquad filter :-)
Christof
On 11.02.2022 23:11, mu...@iem.at wrote:
Zitat von Christof Ressi <i...@christofressi.com>:
That's only half the story. Generally, one shouldn't expect floating
point computations to yield the exact same result with different
compilers/machines. The rounding errors themselves are very small,
but they can accumulate over long periods of time or get amplified by
recursive algorithms.
I've made an alternative implementation [biquad2~] that uses direct
form 1. It shows significantly less noise than the [biquad~]
examples. See attachments.
That's right what you wrote.
However, what worries me is that if I run a Pd vanilla patch on
different Pd versions (i386 or amd64) with the same floating point
precision, I expect the same results.
e.g. the test patch running on Pd-0.52-1-xxx-i386 produces -60dB low
frequency spikes, the identical patch running on Pd-0.52-1-xxx-amd64
produces -34dB high frequency bursts. And that's a realistic simple
situation, a microphone signal feeds a 3rd order high pass filter.
Thomas Musil
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