STOZXFR User Guide
This
screen shot of STOZXFR shows the initial result of mapping an arbitrary analog
filter (actually the 8-th order C-message weighting filter used in voice-band
telephone measurements) to the z-domain. A sampling rate of 20 kHz was
specified; a higher sampling rate will provide a closer match of the z-domain
response to the s-domain response, at the expense of significantly greater
computational load. The z-domain response is in blue,
the s-domain response is in green. The delay characteristics track very
well; the magnitude characteristics differ by less than 1 dB, except that, as
expected, the z-domain response falls off more rapidly than the s-domain
response. Recall that for lowpass and bandpass filters there is a null in
the frequency response at FS/2 as a consequence of using the bilinear-z mapping
method.
There are two tools available for modifying the z-domain response so as to more closely match the s-domain response: the first is the Gain Adjust option which will change the Gain of each z-domain section so that the peak of the z-domain response equals the peak of the s-domain response. The Gain Adjust option can be used in conjunction with the principal tool, namely the adjustment of the z-domain poles and zeros. Before doing any adjustment of the pole/zero values, the Hotlink property for the frequency response plot should be enabled. As the pole values are changed there will be drawn a family of responses indicating how the adjustment is proceeding. The Clear&Replot button should be clicked when the plot becomes too cluttered.
Much greater detail on the features and operation of STOZXFR is to be found in the STOZXFR User's Guide.
An example of the use of STOZXFR is contained in StoZ_Example.pdf