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From: "Talbot Andrew" <ACTALBOT@dera.gov.uk>
To: rsgb_lf_group@blacksheep.org
Subject: LF: RE: Re: Shrinking sounds - fiasco
Date: Fri, 23 Jun 2000 14:27:53 +0100
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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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