Haven't been able to find a clear answer on this. I'm interested in 75-500Hz bandwidth. It's for a tuner(android app) so i want a pretty quick response time.
Is it worth the computational time to high pass the signal?
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$\begingroup$ do you want to detect a single sinusoid in this audio? dunno how HPF would speed things up. for pitch detection, i only HPF to block DC and then toss in some simple -6 dB/oct LPF to help emphasize the periodic portion and attenuate the crap. so for pitch detection of monophonic musical tones, i pass it through a BPF of low Q and a resonant frequency of about 20 Hz. $\endgroup$– robert bristow-johnsonCommented Jan 18, 2017 at 1:23
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$\begingroup$ I'm trying to detect the pitch. I know the HPF will add computational time, I'm wondering if it's worth the time to filter out the DC and low frequency (<50 or 60Hz) components, or if its not really necessary $\endgroup$– Nick54321Commented Jan 18, 2017 at 2:30
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1$\begingroup$ DC blocking is useful in pitch detection. whether you are using some autocorrelation technique or zero-crossing, you need to get rid of DC from the signal if you're gonna be doing pitch detection. and any DC blocking filter is an HPF. and a gentle -6 dB/oct LPF is also useful for preserving periodicity while whacking some of the high-frequency components (that might be noisy). $\endgroup$– robert bristow-johnsonCommented Jan 18, 2017 at 2:41
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$\begingroup$ dunno if you're using MATLAB or some other tool to quickly try things out, but take your monophonic audio (one note at a time, no chords), run it through a BPF with resonant frequency at 20 Hz and 1/2 < Q < 1. look at the waveform going in and coming out. the waveform coming out will look a lot better for determining its period. $\endgroup$– robert bristow-johnsonCommented Jan 18, 2017 at 2:46
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$\begingroup$ im just designing what i want in matlab and implementing/testing in the app. I'm going to be using a frequency domain approach. I have a pretty aggressive LPF(but very linear in the BW im interested in) cutting off sounds higher than 1kHz. It's intended for a guitar so i thought removing high f components would help with spectral density accuracy. $\endgroup$– Nick54321Commented Jan 18, 2017 at 2:52
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2 Answers
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The computational overhead of a band-pass or high-pass (DC blocking) filter on a processor capable of pseudo-real-time musical pitch detection and estimation accurate enough for tuning (+-1 cent?) is probably a small fraction of a percent.
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$\begingroup$ for 1st-order HPF or 2nd-order BPF, for sure. $\endgroup$ Commented Jan 18, 2017 at 3:00
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$\begingroup$ haven't done that benchmark on my smartphone, but on single-board ARMv7-A with NEON extensions, people still do complex MS/s through dozens-of-taps FIRs, so I'm confident my 3x that clock rate, 4x the cores smartphone will be relatively fine at audio rates for more than first or second order BPFs, @robertbristow-johnson. $\endgroup$ Commented Jan 18, 2017 at 9:55
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Yes, it is. If you pickup signals with a microphone you will often see enormous amounts of low frequency signals (air condition, HVAC, traffic, wind, etc.). Even in quiet rooms there tends to be a lot of very low frequency noise.
This noise can dominate the time domain waveform and reducing it can often make your pitch detector more reliable and/or allows for a cheaper or more efficient algorithm.
