Ric Brekne asked for it, so here's the deal on FFTs and TuneLab. The comments are correct that the FFT is used only for the Spectrum Display, which is simply a graph of the FFT power spectrum in the vicinity of the desired pitch. The fine tuning is usually done with the Phase Display, which is functionally like the Accu-Tuner lights because a phase measurement is being made over and over again. It is the phase between the selected partial and an internally-generated ideal signal. In the case of TuneLab, this is all simulated in software. In the case of Accu-Tuner, there is an actual quadrature electrical signal synthesized by the computer chip which is used to strobe transistor switches that drive the LEDs. (I recommend the original Sanderson patent which describes this. It is very readable. I don't have the patent number handy, but you can find it on-line at the Patent Office website.) By watching how the phase drifts forward or backward, the user determines if the piano pitch is high or low. The advantage of a phase-type displa! y is that there is a perfect trade-off between how long you watch the display and how precise the pitch comparison is. The limiting factor is not the technology, but rather the length of the sustain of the note being measured. Every time you strike the note, the phase starts out in a random place, so every strike is a new independent measurement, not a continuation of the measurement. This analysis applies to the Yamaha PT-100, the Conn Strobo-tuner, the Peterson strobes, the Accu-Tuner, and TuneLab. I don't know if Dave or Dean are using a phase-type calculation. Even though both programs use a spinner, which looks like a phase-type display, it is entirely possible to synthesize the movement of the spinner from calculations that are based on FFTs. In principle, it should be possible to extract the same amount of information from a FFT, provided the sample period was optimally-chosen. The description of the CyberTuner in Dean's patents seems to imply that he is using a time-domain bandpass filter to select a particular partial, and then measuring the time between a large number of zero-crossings to determine pitch. Again, in principle, given the optimal bandpass filter and number of zero-crossings, it should be possible to extract the same amount of information as any of these other methods. In my opinion, whether you use quadrature demodulation (like TuneLab and Accu-Tuner) or FFTs, or bandpass filters with zero-crossings, there is no intrinsic difference in the potential of these methods. The differences, if there are any, would lie in the details of how each method was implemented. Robert Scott Real-Time Specialties
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