> > 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?
>
>
> In a polyphase M-fold decimator, you have M polyphase filter coefficient
sets
> E_0 through E_{M-1} that each operate at the outgoing sample rate. Each
section
> is fed from an M-fold downsampler. M phases of the input signal are
obtained
> at the M downsampler outputs by delaying the input of each by a sample.
Then
> each polyphase section is convolved and the results summed. Again
> your computations require M*K*Fs multiplications/second instead of
M^2*K*Fs,
> where Fs is the output sample rate.

This is how I understand it is, too... Don't see the reason for Jim to say
that polyphase only comes into play during interpolation. Could you Jim
please explain me your point of view?

As I see on most diagrams, you have the filter splitted in branches, each
one having a different phase response, thus the term "polyphase", both in
interpolation and decimation filters.

I ask too, "Am I wrong?".

Regards,

--
Jaime Andrés Aranguren Cardona
[email protected]
SanJaaC Electronics
Soluciones en DSP
www.sanjaac.com

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