tone detection advice needed/wanted
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From: steveu on 22 Apr 2010 20:59 >I am doing tone detection of 4 known frequencies using the Goertzel >algorithm. The tones have a large bandwidth that I must be able to detect >them, up to +/-4% of the tone value. To do this the Goertzel is set up to >have large bin width, which makes the SNR not so good. Is there perhaps >another approach that will have similar computation time as the Goertzel, >but allow for better SNR? Your SNR issues relate to the bandwidth of your 4 receivers. Whether they are implemented by the Goertzel algorithm or some other algorithm you are going to get comparable results. The only way to improve those results is to use further knowledge of the thing you are trying to detect. You don't make clear whether you are trying to detect the individual tones, or combinations, and you don't say anything about the tone burst duration or your required detection time. Greater knowledge of these things can make a big difference. If a sustained tone is to be detected, you may be able to look not just for it being within your 4% band, but being steady. If a short but well defined length of tone burst is to be detected, testing the length of the burst can make a big difference to detection reliability. If you are looking for combinations of tones there may be further qualities which you can look for. If they start out with accurate frequencies, but suffer up to 4% doppler shift, a valid combination will never be tone A near the low end of its 4% range + tone B near the high end of its range. Homing on the details of the signal in this heuristic way can greatly improve detection reliability. Steve
From: Gerold Schrutz on 23 Apr 2010 01:24 "jacobfenton" <jacob.fenton(a)n_o_s_p_a_m.gmail.com> schrieb im Newsbeitrag news:WoGdnezIvZLx5U3WnZ2dnUVZ_gWdnZ2d(a)giganews.com... >I am doing tone detection of 4 known frequencies using the Goertzel > algorithm. The tones have a large bandwidth that I must be able to detect > them, up to +/-4% of the tone value. To do this the Goertzel is set up to > have large bin width, which makes the SNR not so good. Is there perhaps > another approach that will have similar computation time as the Goertzel, > but allow for better SNR? > > Thanks. > > -Jacob Fenton Hello Jacob, how about using a window in front of the Goertzel? Choosing the right window, you can control the bandwidth without changing the length of the Goertzel computation. Leaving the lenght of the Goertzel computation should give you better S/N ratio. BR Gerold
From: dsp314159265 on 24 Apr 2010 21:47 Hopefully this is not what you meant by "Goertzel is set up to have large bin width" but did you try: and IIR filter with an adjustable BW around the frequencies of interest by placing two poles just inside the unit circle: alpha*exp(j*(w-deltaw)) and alpha*exp(j*(w+deltaw)). alpha is close but less than 1 and the 4% tolerance can be met by changing deltaw. -k >On 22 apr, 18:25, "jacobfenton" <jacob.fenton(a)n_o_s_p_a_m.gmail.com> >wrote: >> I am doing tone detection of 4 known frequencies using the Goertzel >> algorithm. The tones have a large bandwidth that I must be able to detect >> them, > >The term 'tone' is usually used about (nearly) monochromatic >signals. A 'tone with a wide bandwidth' is pretty much a >contradiction in terms. > >What kinds of signal are you *really* looking for? > >> up to +/-4% of the tone value. > >What 'value' is this? Amplitude? Frequency? Something else? > >> To do this the Goertzel is set up to >> have large bin width, which makes the SNR not so good. Is there perhaps >> another approach that will have similar computation time as the Goertzel, >> but allow for better SNR? > >It depends on what signals you are working with and what >you attempt to do. > >Rune >
From: jacobfenton on 26 Apr 2010 11:32 >>I am doing tone detection of 4 known frequencies using the Goertzel >>algorithm. The tones have a large bandwidth that I must be able to detect >>them, up to +/-4% of the tone value. To do this the Goertzel is set up to >>have large bin width, which makes the SNR not so good. Is there perhaps >>another approach that will have similar computation time as the Goertzel, >>but allow for better SNR? > >Your SNR issues relate to the bandwidth of your 4 receivers. Whether they >are implemented by the Goertzel algorithm or some other algorithm you are >going to get comparable results. The only way to improve those results is >to use further knowledge of the thing you are trying to detect. > >You don't make clear whether you are trying to detect the individual tones, >or combinations, and you don't say anything about the tone burst duration >or your required detection time. Greater knowledge of these things can make >a big difference. If a sustained tone is to be detected, you may be able to >look not just for it being within your 4% band, but being steady. If a >short but well defined length of tone burst is to be detected, testing the >length of the burst can make a big difference to detection reliability. If >you are looking for combinations of tones there may be further qualities >which you can look for. If they start out with accurate frequencies, but >suffer up to 4% doppler shift, a valid combination will never be tone A >near the low end of its 4% range + tone B near the high end of its range. >Homing on the details of the signal in this heuristic way can greatly >improve detection reliability. > >Steve > > > The tones are from an FM signal, so they are individual or combined, depending on how many tones are being sent. I will have to inquire more about the 4%, if its due to doppler or not, it is not specified in that detail. I appreciate your response.
From: jacobfenton on 26 Apr 2010 11:35
>On 22 apr, 18:25, "jacobfenton" <jacob.fenton(a)n_o_s_p_a_m.gmail.com> >wrote: >> I am doing tone detection of 4 known frequencies using the Goertzel >> algorithm. The tones have a large bandwidth that I must be able to detect >> them, > >The term 'tone' is usually used about (nearly) monochromatic >signals. A 'tone with a wide bandwidth' is pretty much a >contradiction in terms. > >What kinds of signal are you *really* looking for? > >> up to +/-4% of the tone value. > >What 'value' is this? Amplitude? Frequency? Something else? > >> To do this the Goertzel is set up to >> have large bin width, which makes the SNR not so good. Is there perhaps >> another approach that will have similar computation time as the Goertzel, >> but allow for better SNR? > >It depends on what signals you are working with and what >you attempt to do. > >Rune > The tone frequencies can change up to 4% and I have to still be able to detect them. |