On Thu, 16 Dec 2004 09:21:11 -0500, Jim Thomas <[email protected]>
wrote:

>Jaime Andrés Aranguren Cardona wrote:
>> "Jim Thomas" <[email protected]> escribió en el mensaje
>> news:[email protected]..
>>
>>>Jaime Andrés Aranguren Cardona wrote:
>>>
>>>>What else could I try, guys? I'd really appreciate if you can take a
>>
>> look at
>>
>>>>my code, and help me find out where the mistakes can be, or provide me
>>
>> with
>>
>>>>some reference C code.
>>>>
>>>>Thanks you very much in advance,
>>>
>>>Did you see Grant's multirate code on dspguru.com?
>>>
>>
>>
>> Hi Jim,
>>
>> Yes I did. It is not polyphase, right? I'd love it was... Any example in C
>> with ployphase implementation?
>
>The interpolation code on dspguru is most definitely polyphase.
>
>My understanding is that polyphase only comes into play during interpolation.
>It's only during interpolation that you get the opportunity to skip through the
>coefs - essentially choosing a phase of the impulse response. In decimation you
>work on contiguous samples, but only calculate the outputs you're going to keep.
>
>Am I wrong?

I'm coming in in the middle of this and there's already a lot of good
responses here, but:

Polyphase filters are commonly used in decimating applications when
the decimated samples need to be interpolated somewhere in between
where the original samples were. Many modern communications systems
do this for symbol recovery, where an oversampled input is
simultaneously phase-locked and downsampled to the signal symbols.
Polyphase filters are great for this since the symbol rate can be
changed without changing the ADC sample rate and the related
anti-alias filters, etc.


Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org