Direct-Recording Frequency and Amplitude Meter for Analysis of Musical and Other Sonic Waveforms
P.A. Tove, B. Norman, Leif A. Isaksson, Jan Czekajewski · The Journal of the Acoustical Society of America · 1966
The notation of frequency and time relations in the study of musical phenomena produced by single unisonous instruments or song is discussed. The nature of the pertaining electrical waveforms in recorded music of this type, and especially the possibilities of extracting the fundamental and measuring and recording its frequency (pitch), is treated. A transistorized instrument performing this function and having fast response to changes in frequency is described. The output from this meter is fed to a fast ink recorder to show the frequency variations on a convenient diagram as an objective form of music printing, or “visible music.” As a complement, the original waveform is rectified and plotted logarithmically in a second channel on the recorder to show the amplitude variation. The frequency compass covered in a single registration is normally a single octave, which can start at any consecutive minor-third interval (frequency ratio 6/5) in the range A1 (55 cps) to A6 (1760 cps). Changes with time can be recorded with a detail down to about 0.01 sec, and frequency differences of a small fraction of a half-tone can be measured. The dynamic range of the registration of amplitude is ≈40 dB. A third trace on the recorder is a 50-cps waveform used for time marking. The frequency and amplitude levels of the registration can be checked with a calibrator. This is a self-stepping oscillator giving 7 tones, each of 1 sec duration and separated by whole-tone intervals. Thus, it covers one octave and this can be chosen to start at 55, 110, ⋯ or 1760 cps. The amplitude calibration is logarithmical with manually chosen levels.