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Audio Talkthrough demo -- distortion with fir filter

Question asked by TomA Employee on Apr 14, 2009
Latest reply on Feb 10, 2010 by TomA

I have modified the talk through C program included with the EZ-KITs (537) and
am trying to implement a very simple low pass FIR filter which I
designed in Matlab and implemented in the process data function, all
done in C.  Unfortunately, I get a considerable amount of distortion on the
output and not the desired filter response.

I suspect that the distortion has something to do with the internal data
representation since I believe the 1871 and 1854 data converters treat
the data as 24-bit, unsigned integers and my FIR calculations are using
single-precision floating point.  I have tried several approaches using
numeric format conversions to try and ensure the data formats, but none
successfully.  I also read that there are "fract" functions included
within the C run-time libarary, but I have avoided them since I am just
trying to demonstrate basic filter design and implementation using C.