I change the parameters to change the vibrato frequency, and depth. I wish to put a random number generator in the speed parameter, so that the frequency is constantly changing, and somehow get the pitch to go up and down randomly. I have several VHS captures with this kind of warble in the sound that I wish to recreate digitally without having to record my audio to a VHS tape on my VCR in SLP mode, and then capture it to my computer, which requires patience and lots of cables. (I have all the stuff, it just takes a while.)
If I look at a tone recorded to VHS and captured, the frequency will jump around a little, not staying constant, and does not follow any recognizable pattern.
Here is a screenshot of a note in Spectrum view, and shows the inconstant tone due to variation in tape speed.
I’m using the linear audio track on my VCR, which does not get much of anything from the head drum. The capstan is rotated by a motor, which has a fly-wheel, but the tape does not move at an exactly constant speed. Since the audio is recorded linearly, the variations during recording add up with the ones during playback. VHS HIFI audio, however, is recorded as an FM track mixed with the video tracks, which gives, well, Hi Fidelity audio, basically no noise, nearly high frequency response, etc. The tape would be running at about 1.1 centimeters per second, and I will provide an audio sample of what it sounds like.
Also, the tape reels move extremely slowly, the take-up reel spinning once only every 8 seconds or so. Maybe the pinch roller would run at about 22RPM, but not much else. On the RPM value in the original nyquist prompt script, that was pulled off of this website from somewhere about a year ago, where I don’t remember. The RPM is not actually RPM, it is simply the vibrato speed in 60ths of a second. A value of 60 would give a frequency modulation of 1 cycle per second.