Does anybody know if it is possible to calculate a FFT on a certain bandwith, less that the sampling frequency? For example: I only have the resources to do a 64 point FFT, but I know the energy I want to measure is between 1kHz and 2kHz (fs = 8 kHz). Can I do a 64 point FFT on the band 1kHz 2kHz ? Rgds JEAN
FFT on a narrow band
Started by ●November 3, 2003
Reply by ●November 3, 20032003-11-03
At 03:50 AM 11/3/2003, Jean Viljoen wrote: >Does anybody know if it is possible to calculate a FFT on a certain >bandwith, less that the sampling frequency? > >For example: I only have the resources to do a 64 point FFT, but I know >the energy I want to measure is between 1kHz and 2kHz (fs == 8 kHz). Can >I do a 64 point FFT on the band 1kHz 2kHz ? > >Rgds >JEAN > > Yes, Its called a zoom FFT. Try a Google search on this topic and I > think you will find your answer. > >Here is a link to the basic idea: http://www.numerix-dsp.com/zoomfft.html Al Clark Danville Signal Processing, Inc. -------------------------------- Purveyors of Fine DSP Hardware and other Cool Stuff Available at http://www.danvillesignal.com
Reply by ●November 3, 20032003-11-03
Jean, Check out the Chirp z-transform. I'm not sure, but I think this can do what you want. Regards, Tony ______________________________ Tony Zampini (tony@tony...) Director of Engineering DSP Global 33 Plan Way, Bldg. #4 Warwick, RI 02886 Tel. 401-737-9900 FAX: 401-739-4197 www.dspglobal.com ----- Original Message ----- From: "Jean Viljoen" <jean.viljoen@jean...> To: "Audio DSP Group" <audiodsp@audi...> Sent: Monday, November 03, 2003 4:50 AM Subject: [audiodsp] FFT on a narrow band > Does anybody know if it is possible to calculate a FFT on a certain > bandwith, less that the sampling frequency? > > For example: I only have the resources to do a 64 point FFT, but I know > the energy I want to measure is between 1kHz and 2kHz (fs == 8 kHz). Can > I do a 64 point FFT on the band 1kHz - 2kHz ? > > Rgds > JEAN > > > > > > > > _____________________________________ > Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. > > _____________________________________ > About this discussion group: > > To Join: audiodsp-subscribe@audi... > > To Post: audiodsp@audi... > > To Leave: audiodsp-unsubscribe@audi... > > Archives: http://groups.yahoo.com/group/audiodsp > > Other DSP-Related Groups: http://www.dsprelated.com > > > ">http://docs.yahoo.com/info/terms/ > > >
Reply by ●November 3, 20032003-11-03
If you want full spectral resolution in the band from 1kHz to 2kHz (32 frequency bins for a 64 point FFT) then do the following... What you could try is first bandpass filter the signal between 1kHz and 2kHz*, then decimate by 4 to give a sample rate of 2kHz (now the spectrum will be re-mapped: 1kHz to 2kHz becomes 0 to 1kHz). Performing a FFT will give the spectrum from 2kHz to 1kHz. * Note: you should suppress all components below 1kHz and above 2kHz to avoid aliasing, so your pass band will be less than 1kHz. Alex Young DSP software Engineer Consultant for Philips Digital Systems Laboratories To: "Audio DSP Group" <audiodsp@audi...> cc: (bcc: Alex Young/LEU/PDSL/PHILIPS) Subject: [audiodsp] FFT on a narrow band "Jean Viljoen" Classification: <jean.viljoen@jean... > 03/11/03 10:50 Does anybody know if it is possible to calculate a FFT on a certain bandwith, less that the sampling frequency? For example: I only have the resources to do a 64 point FFT, but I know the energy I want to measure is between 1kHz and 2kHz (fs == 8 kHz). Can I do a 64 point FFT on the band 1kHz ? 2kHz ? Rgds JEAN _____________________________________ Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. _____________________________________ About this discussion group: To Join: audiodsp-subscribe@audi... To Post: audiodsp@audi... To Leave: audiodsp-unsubscribe@audi... Archives: http://groups.yahoo.com/group/audiodsp Other DSP-Related Groups: http://www.dsprelated.com ">http://docs.yahoo.com/info/terms/