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Set up a sig genny and test him out


Much easier to say the test tape is stretched.
Perhaps perfect pitch testing would only work by playing the likes of JSB
Tocatta and Fugue in D major, not pure tones

How come I cannot google the rpm of an audio cassette capstan? A calibrated
strobe and tipex mark on the capstan periphery should give a definite
answer
(assuming the spindle is clean and not worn).
It should be determinable from tape speed of 1 7/8 in per sec and spindle
diameter, that is about 1.9mm, but what should it be to 0.1 percent
accuracy?



pi times diameter gives the circumference of the capstan.
1 7/8 ips divided by circumference gives the required revolutions per
second.
You can measure the RPS of the flywheel, but that does not guarantee that
the tape is traveling at 1 and 7/8.
The bottom line is that you need a calibration tape and a frequency counter.
You can measure the frequency at several spots on the tape to see if the
tape pack and such, has any effect on speed.
BASF used to make an excellent calibration tape. I do not know if they are
still available, and they are not cheap.