[linux-audio-dev] [ann] guitar preamp plugin, v2

[Tim Goetze]

me wrote:

>Steve Harris wrote:
>
>>On Sun, Nov 02, 2003 at 10:49:17PM +0100, Tim Goetze wrote:
>>> the frequency response is mostly due to the oversampling filters;
>>> unfortunately i am at a loss for good realtime-compatible design
>>> methods for those. it would well be possible to recalculate them
>>> (chebyshev prototypes) but that would take quite a few cycles, and
>>> knowledge about how to move the ripple/s in a chebyshev design
>>> (anyone?).
>>
>>Have you tried polyphase filters? I've never used them but I've heard they
>>are good for oversampling.
>
>i don't have any precise cycle-consumption figures (a good reason to
>try the polyphase filters one day) but i seem to remember having
>figured that they come at equal or bigger cost for comparable stopband
>attenuation. 

i feel the need to clarify/correct myself: the filters employed are
not chebyshev designs, they were designed the same way as 'unmatched':
frequency response given, iteratively approximate the filter.

they do a lot better than chebys of the same order, but it's quite
impossible to recalculate their coefficients at runtime. if that is
demanded, the polyphase design probably wins easily.

tim