[sdiy] Looking for cheap lowpass filter algorithm

[Seb Francis]

Magnus Danielson wrote:
>
>
> You *ARE* using all the 48 kHz input-data, not just all of the 48 kHz output
> data of the filter. Every odd sample will only go through the odd taps of the
> filter while every even sample will only go through the ever taps of the
> filter, where as normally all samples will go through all taps of the filter.
>
>   

Ahh, it suddenly becomes clear to me!

And I have it all working nicely now .. no more high frequency distortion :)

In the end I found a bit of software called "ScopeFIR" to calculate the 
FIR coefficients.  Seems to be a very comprehensive program for this 
sort of thing.

Thanks for your help,
Seb