Ron wrote in message
...
N_Cook wrote:
Arfa Daily wrote in message
...
"N_Cook" wrote in message
...
Assuming my test tape is stretched (I doubt it , as it would have to
be
even
stretch the whole length).
I normally test speed monaurally so the beats are unmistakable. That
is
1KHz
test tape output and floating accurate 1KHz sine signal both fed into
one
headphone cup. Easily gives 0.1 percent resolution (assuming test tape
is
ok).

If I record accurate 1KHz tone onto a blank tape for exactly ( to
human
reaction time accuracy) 100 seconds. Then replay for beats of 1Hz or
so
and
output lasts for 100 seconds +/- reaction time then is the speed
correct?
I
suspect that repeating this process with the speed regulator changed ,
say
5
percent, would also give "correct" speed, that time also


Does anyone know how much effect types and thickness (play duration
C30
to
C90) have on replay speed perhaps in conjunction with too soft or too
hard
pinch wheel rubber ?


I just use a speed test tape from Konig. It has a strobe wheel behind
what
would normally be the tape viewing window. Very easy to see an accurate
setting for the speed, and virtually instant comparison between forward
and
reverse. Also easy to see any cyclic variations in speed, or long term
drift.

Arfa




Strobing of what rotational part against what reference?
How do you know if the tape is stretched?



It doesn't matter if the tape is stretched, the tape speed is governed
by the rotational speed of the capstan.
If the tape were stretched you would have to adjust the capstan speed to
get the right playback pitch on that particular tape tho I doubt it
would be very noticable.
Somewhere I still have a cassette with 100 hz on one side and 8k on the
other, plus a strobe disk visible through the window on the 100 hz side.
You set the capstan speed by measuring the 100 hz on playback. The 8k is
for head alignment. The strobe disk is driven by the capstan.

Quite often the playback speed would be adjusted to be correct, followed
by complaints from the customer that all his tapes now seem to play at
the wrong speed!

Ron(UK)


Whatever touches the capstan spindle could wear and if the reference source
for stobing is a mains lamp, that is only set for (UK) 50x60x60 cycles per
hour (for synchronous clocks) and short term only +/-0.5 percent targetted
frequency.

I have the related problem of someone who says he has perfect pitch.