Chapter 7
Sampling Rate Conversion
The
DAT-Link
provides real-time conversion during recording or playbackbetween
the sampling rate used on the digital audio I/O's and any rate requested by the
user. Based on the requested rates, the software dynamically creates a conversion
program which makes optimal use of the DSP32C digital signal pro cessor in the
DAT-Link
. Note that the conversions are not limited to integer fractions; any rate
can be chosen and obtained by the
DAT-Link
.
Since the sample rate converters are generated dynamically, it is dicult to predict
the exact sp ecications of the converter without lo oking a specic examples (as will
be done in Section 7.1). However, the following information will be adequate for
most purposes:
The converter contains a low pass lter with a stopband frequency of
f
stop
=
min(
f
s
1
;f
s
2
)
2
where
f
s
1 and
f
s
2 are the input and output sampling rates.
The attenuation of the lter in the entire stopband, will b e approximately 90
dB. This value can b e changed, as will be described below.
The passband ripple should b e ab out 0.0003 dB.
The lter will always be linear-phase.
The passband frequency will be chosen as high as p ossible, minimizing the
transition band. The exact frequency depends on the
diculty
of the requested
conversion. In all cases, the software uses as much of the DSP32C's resources
as possible to obtain the sharp est p ossible lter cuto.
The
diculty
of the conversion is aected by the following:
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