A PD patch was created for the purpose of measuring the modulation depth (in semitones) produced by various changes in PMS and PMD on the TX7. The TX was set up so that only one oscillator was active - producing a sine tone, which helped avoid any ambiguity created by more complex tones, and improved the accuracy of the measurements. A frequency of 880Hz was used in order to avoid any poor low frequency performace in the pitch detection process. An FFT based pitch detector (fiddle~) was used with an FFT window size of 1024. For smooth changes in frequency, this gave a ‘worst case’ accuracy of +/-3cents, and a time resolution of 23ms per frame. As the LFO wavelength was 8 seconds, and the maximum modulation depth was 2 octaves, this gave a maximum possible change of 7 cents between analysis frames. Although not ideal, this was considered to be an adequate level of accuracy for good ‘best fit’ curves to be produced.
[Attachment][1]
[1]: /jamie_bullock/harvey/TX7-data-1.tar “TX7 measurements:
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