Well, the way I do it is to use a mixed down frequency centred on zero
and use low pass filtering to give bandpass when mixed back up for
listening. As described the method would need some low pass filtering
as part of the initial mixing down process.
Filtering may well also be needed in the final upconversion process
Andy
3) and 4) can be taken together - if using an FIR filter, the
filtering
process needs to be done for each decimated sample only - this saves
considerable processing overhead for the long filter tap lengths
necessary
If you plan to combine steps 3) and 4) by doing first decimating and
then narrow band (sub-Hz) filtering, shouldn't you low pass filter the
signal produced by the mixdown at 2) to have a bandwidth less than 15
Hz for the final 31.25 Hz sample rate to meet the Nyquist criteria ?
Paul OH3LWR
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