ISSUE: floating-point-inaccuracy of low frequency filters with low
frequency signals in pd vanilla
The patch "Test_HP3_butterworth_@_20_Hz.pd" is part of the Live
Electronic of K.H.Stockhausens piece Mikrophonie I.
My colleague David P. told me, that there occur hearable noise,
distortion, oscillations and rustling during perfoming this piece.
The test-patch is a 0.1 Hz oscillator sourcing a highpass filter
3.order with butterworth characteristic at 20 Hz.
Try this patch with pd-0.52-1-msw-i386 and amd64 aka 32-bit and 64-bit
and older pd versions.
The 32 bit version has 20 dB less noise than the 64 bit version (and
no oscillations).
Double precision filters of iemlib ("hp3_butt_dp~.pd") have less noise
than single precision filters.
IOhannes z. and Chrostof R. figured out, it depends on compiler
options -ffast-math and / or -fassociative-math.
Some screenshots are added.
have fun
Thomas Musil
