72 Sampling Rate Conversion
Whether stereo or mono conversion is requested.
The magnitude of the input and output rates. For the same ratio, lower rates
are easier.
The ratio between the rates; medium ratios (2-5) are easiest. Ratios that are
very large may b e constrained by the amount of memory available to the DSP.
Whether the ratio is an integer, a small fraction, or neither. Integer and
fractional ratios are marginally easier in most cases. If the ratio is very large
(or very small), then integer ratios will place less demand on the DSP.
7.1 Sp ecications of Some Example Converters
The following table gives the sp ecications for some example conversions. Note
that these sp ecications are intended as an indication of p erformance only, due
to the dynamic methods used to allocate memory and resources, the exact results
you obtain may dier slightly. Exact impulse responses can be measured using the
nagetfilter
command described in Section 10.5.
7.2 Changing the Filter Resp onse
By default, the software uses a maximally-sharp, lowpass lter as described ab ove.
However, it is p ossible to specify an arbitrary lter resp onse with the single proviso
that its passband frequency will never exceed that of the default lter. The desired
response is given as points on the magnitude response curve. For example, the lter
shown in Figure 7.1 was specied using the string:
0@-90,200@-90,400@0,3400@0,3600@-90
The lter string should be entered in your
.datlinkrc
le. For example, adding the
line:
naplay.filter*: 0@-90,100@0
would use a 100 Hz high-pass lter whenever
naplay
is used for output to the
DAT-Link
.
Dierent lters can be specied for dierent sample rate conversions by using an
option name of the form:
pgm.filter.irate.orate
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