Subject: Re: Robust method of fundamental frequency estimation. From: "Maher, Rob" <rmaher@xxxxxxxx> Date: Fri, 2 Feb 2007 11:22:25 -0700 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>Some of the inexpensive tuners measure the zero crossing rate (time domain) of the fundamental. In other words, they measure the waveform period directly. PC software tuners often use the same approach. Even with a relatively low digital sampling rate (e.g., 44100 Hz) the number of samples per half-cycle for guitar string frequencies (~80 - ~300 Hz) is more than 100 samples, and this is large enough that reasonably good tuning can be accomplished. Averaging over several cycles gives a bit of improvement, too. Regarding the use of FFT-based fundamental frequency estimation: one of the advantages of using higher frequency harmonics in the estimation process, rather than just the fundamental, is that the uniform frequency resolution (call it dX) of the DFT can be exploited. For example, if the frequency of the third partial of a harmonic waveform is found to be (X +/- dX) Hz using an interpolated FFT (where dX represents the error in estimating the frequency) the fundamental estimate is thus X/3 +/- dX/3, which is improved in resolution. Note: this requires figuring out which partial represents which harmonic (see the Two-Way Mismatch article), and doesn't help if the waveform is actually aperiodic (such as the piano). There are some ways to take into account the stretched partial frequencies due to string stiffness, but it is pretty empirical. Rob Maher -----Original Message----- From: AUDITORY - Research in Auditory Perception [mailto:AUDITORY@xxxxxxxx On Behalf Of Bob Masta Sent: Friday, February 02, 2007 7:14 AM To: AUDITORY@xxxxxxxx Subject: Re: Robust method of fundamental frequency estimation. Dear list: As long as we are on this topic, does anyone know what method those $20 guitar tuner devices use? I n my limited experience (observing others) they seem to work pretty well for guitars. In fact, I'd have to say "amazingly well", based upon my pre-computer attempts at pitch extraction for stringed instruments. <g> Has anyone tried one on low piano notes? Best regards, Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis www.daqarta.com Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!