On 4/28/07, Tim Ellison <[EMAIL PROTECTED]> wrote: > > On the web page, it states that the filter shape factor for a 500 Hz > filter is 1.35:1 and a 2.6 KHz filter is 1.06:1. But I believe that > these values were taken at 48K sampling rate with a 1024 DSP filter. > > I don't have a scope or a signal generator to check this, so I am asking > if anyone has done (or would consider doing) an analysis of the filter > shape factor with different DSP buffer sizes and sampling rates? I > would be very interested in seeing how the shape factor varies with > these parameters at a 500 Hz and 2.6 KHz filter width?
The shape factor is proportional to the sample rate divided by the filter length. If you double the sample rate but keep the filter length the same, the shape factor goes up. If you keep the sample rate the same but double the filter length, the shape factor goes down. The reason I only say proportional is that what changes the most in this picture is the transition bandwidth. The back of the envelope here says, at 48kHz, difference between 1.35:1 at 500Hz and 1.06:1 at 2.6kHz is about 30Hz in the transition bands at -60dB. Not much. The rule of thumb is, for a given shape factor, if you double the sample rate, you need to double the filter length to keep the same shape factor. 73 Frank AB2KT -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/attachments/20070428/dcef2ad3/attachment.html _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
