Subject: [linux-audio-dev] Software filter engines for high end audio
From: Anders Torger (torger_AT_ludd.luth.se)
Date: ke helmi 16 2000 - 06:18:17 EST
Are there any FIR (or IIR or Warped IIR or Warped FIR) filter engines out
there, suitable for audio applications? I'm asking, because I am working
on an own, and would like to know if there are any more out there. My
software currently only implements a Warped FIR filter, which can take 16
- 24 bit audio as input and produces 24 bit output. Later I will add a FIR
filter, capable of about 3000 taps on a 266 MHz Pentium II (16 bit 44.1
kHz input, 24 bit output, and no risk for overflow), which however is
limited to only 16 bit samples as input. The high performance is achieved
from analysing the filter coefficients and generating assembler code
especially fit for the given set, which is then compiled and attached to
the filter engine. The release of the FIR filter is at least a few weeks
away though, since I need to finish an ALSA driver for the RME Digi96
digital I/O first.
I plan to use the filter in software driven room correction systems, and
in fact I have already a working prototype based on the WFIR filter, found
at http://www.ludd.luth.se/~torger/filter.html. Complete with an MLS
measuring system. All GPL'd of course. I'd love to get comments and
questions about the system :-)
The plan is to make a room correction system based on the FIR filter
later, which will be able to correct phase problems, as well as magnitude.
The current system does not correct phase.
I find this area very interesting, since it is possible to make your Linux
machine (which must be rather fast, I use a dual P2 266, one processor per
channel) into a room correction system that is on par or surpasses
commercial systems that cost around 4000 US dollars. The problem so far
has been the lack of quality digital I/O cards for Linux, but soon we will
have a driver for RME Digi96, the best alternative (price/performance) I
have found for two channel systems.
/Anders Torger
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