Re: Huge resampling factors

Don't get totally locked into the thought that you must resample in
integer ratios, despite all the DSP books showing that approach.
Resampling is interpolation, and nothing says that you have to only
calculate, via interpolation, at periods of 1/n.

So why do we (well, the books, etc.) choose integer ratios? Well, if you
pick an *arbitrary* ratio, it makes a fixed windowed-sinc (or whatever)
table impractical. It also makes it difficult to suggest that the user
do things insert a fractional number of zeros before filtering. For the
latter, we never really insert the zero anyway (we use polyphase
techniques, etc.). For the former, you can either caluate the factors as
needed (usually a bad idea, speed-wise), or just make a reasonably-sized
table and interpolate between the points to get any ratio you want.
Linear interpolation works fine because a well-oversampled windowed-sinc
function is pretty smooth from point to point.

Google for Julius Smith's bandlimited interpolation webpage.


In <Qq6dnbznoLs3RcHeRVn-2w@xxxxxxxxxxxx> stilghar wrote:
> Hi,
>
> I've to resample a signal from 16.3676 MHz to 4.096 MHz. If I'm not
> wrong I should interpolate by 10240 and then decimate by 40919. But,
> these are huge numbers! Is there any other way of doing it?
>
> By the way, due to performance requirements I couldn't acces the whole
> signal at a time, so I have to do the resampling process by blocks.
>
> Thank you.
.

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