Sampling Rate Conversion - Townshend Computer Tools DAT-Link User Manual

Chapter 7

Sampling Rate Conversion

DAT-Link
The provides real-time conversion during recording or playback between
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 processor in the
DAT-Link
. Note that the conversions are not limited to integer fractions; any rate
can be chosen and obtained by the
Since the sample rate converters are generated dynamically, it is dicult to predict
the exact speci cations of the converter without looking a speci c 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

where 1 and 2 are the input and output sampling rates.
f f
s s
The attenuation of the lter in the entire stopband, will be approximately 90

dB. This value can be changed, as will be described below.
The passband ripple should be about 0.0003 dB.

The lter will always be linear-phase.

The passband frequency will be chosen as high as possible, 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 sharpest possible lter cuto .
The diculty of the conversion is a ected by the following:
DAT-Link
.
= min( )
f ; f
s s
1 2
f
stop
2