Hi all, I have a little question... Is there a trade-off beetween the cut-off frequency of an IIR filter and it's sampling frequency ? In practice I have noticed that we cannot have a relation more than Fs = 100 * Fc with 16 bits coeffcients... Is there a theoritical proof ? Thanks
Cut-off frequency and sampling frequency IIR filter
Started by ●March 8, 2007
Reply by ●March 8, 20072007-03-08
On 8 Mar, 15:02, patrick.me...@dmradiocom.fr wrote:> Hi all, > > I have a little question... > > Is there a trade-off beetween the cut-off frequency of an IIR filter > and it's sampling frequency ?In principle: No.> In practiceYes. It has to do with imperfect numerical computations in real-life CPUs. All number systems have more or less inherent inaccuracy, depending on the number formats they use.> I have noticed that we cannot have a relation more than Fs > = 100 * Fc with 16 bits coeffcients... > > Is there a theoritical proof ?I would be surprised if there is. These things vary, depending on the filter structure and a lot of other factors. Apparently -- I haven't tried these things myself -- ladder realizations are more accurate, in certain respects, than naive direct form 1 or 2 structures, given the same numerical formats. But now we are entering the field of expertice of the seasoned DSP (as in specialized processor) programmers... Rune
Reply by ●March 8, 20072007-03-08
patrick.melet@dmradiocom.fr wrote:> Hi all, > > I have a little question... > > Is there a trade-off beetween the cut-off frequency of an IIR filter > and it's sampling frequency ?It is the matter of the practical implementation.> In practice I have noticed that we cannot have a relation more than Fs > = 100 * Fc with 16 bits coeffcients...It is possible, however the structure of the filter has to be modified for that purpose.> Is there a theoritical proof ?The gain of the recursive part of IIR filter is approximately Q*(Fs/Fc)^2. The precision problems are the direct consequence of that. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com