the 'filter.h' library does not support cascaded biquadratic filters (ie 2nd order IIR filters). Does anyone have such filters available? Preferably both for fract16 and fract32 data.
direct form I with all coefficients /2 so that they are <1. Additionally the numerator coefficients are optionally scaled up (by power of 2) so that significant digits/bits are retained for low frequency filters. 32 bit coefficients are plenty. You could also use 16 bit coefficients and 'AB2t' structure (again with coefficients scaled <1). Either of these will work below 100Hz even with 192kHz sampling frequency.
There was a Analog devices Plattform called visualAudio with such functions like biquads etc. included
32bit and 64bit for Blackfin or Floating libs for sharc.
i dont know if this visualaudio studio is available currently on the Internet.
To address Christoph's uncertainty about VisualAudio - it was made obsolete some time ago, and is no longer available from Analog Devices. We typically recommend customers look at Audio Weaver from DSP Concepts, which is similar to VisualAudio, but actively developed and maintained.
Thanks for the responses...I wrote my own in assembler
fine, what Kind of IIR have you implemented(32/48/64bit), and how effective they are.
32 bit data, coefficients and state - takes 12 cycles/biquad/sample - this is more than adequate for any real audio signal which is effectively limited to about 120 dB SNR
hi ! thanks for info - what Kind of IIR-structure. and how are the coeffs. coded/calculated
We have observed some artefacts with 32bit filters in the lowfreq.range < 100Hz.
Retrieving data ...