Speed measurement test cassette

Does anyone have a source to purchase a good quality speed calibration cassette tape? I used to have an older Nakamichi test tape, but it was worn out to the point it was inaccurate. I was looking for the highest quality one I could find, as I frequently transfer from tape to computer and want accurate result - I'm suspicious of the tapes being sold on line, mainly because they're duplicated or generated from lower quality tape decks which are already inaccurate.
 
One way might be to make a tape:
You need a cassette you can unscrew, record a continuous tone on it, doesn't matter what.
Take it apart carefully and unroll the tape, marking it every metre on the back with a marker pen.
Then carefully use a physically small permanent magnet to erase the tape at each mark.
Respool and reassemble - the recording will have a drop-out every 21.00 seconds if played at 1 7/8" per second.
(well 20.9974 seconds if you think you'll be able to get 500ppm accuracy or better!)

You might be able to spot the marks through the cassette if its transparent.
 
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Clever method. Compact cassettes run at 3 3/4"/sec. Perhaps it is more convenient to create a test tone recording on a calibrated studio recorder.
Once I measured the playing time of a 30sec cassette with a stopwatch. I don't know how accurately is the length measured at manufacturing.
If you record and play back on the same machine, absolute speed accuracy does not matter.
 
Email or PM me, I make probably the best current Speed/W&F cassettes, with the residual W&F below 0.06% not wtd, 0.03% DIN wtd, 0.015% WRMS . Good enough to check if the Nakamichi Dragon performs as it should. Here is the W&F graph of a well serviced Dragon using one of my cassettes.

Cheers

Alex

Dragon_S30A.gif
 
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You're both missing that there are two standards:

1.875 (aka 1 7/8) inches per second (4.7625 cm/s)
4.75 cm per second
Delving into this it appears the standard is metric 4.75cm/s, which is "nominally" 1 7/8"/sec (0.26% different). Why Phillips didn't just choose 5cm/s defeats me in that case - much less likely to lead to 0.26% error confusion! (Having said that cassette tape can stretch more than that!!)

Its interesting that mag tape chose to go down the powers-of-two route to speed standards and vinyl chose 78/45/33.3/16.7 rpm.

And why is tape speed imperial? It was a German invention after all.

I correct my value above to 21.05 seconds per metre.
 
To my knowledge there is only one speed standard for the compact cassette - 1 7/8 ips or 4.7625 cm/s. I suspect that the choice of the standard R2R speed step (30-15-7.5-3.75-1.875 ips) was at least partially due to cassette duplication requirements, it was much simpler to run duplication R2R recorders at standard R2R speeds.

Cheers

Alex

P.S. 3.75 ips or 9.525 cm/s is not a standard speed for Compact Cassette. However it is much more suitable speed for the tape used in cassettes, providing the optimum performance. A properly designed 3.75 ips cassette deck can rival best R2R decks working at 15 ips,
 
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There was double-speed Tascam multitrack cassette decks that ran at 3 3/4 IPS. I read they had to get permission from Philips (designer of the original Compact Cassette) to do that.
I've never heard of the 4.75cm speed, but at 1 percent slower than the "other" standard, it would appear to be (by the standards of back then) pretty much the same.
To my knowledge there is only one speed standard for the compact cassette - 1 7/8 ips or 4.7625 cm/s. I suspect that the choice of the standard R2R speed step (30-15-7.5-3.75-1.875 ips) was at least partially due to cassette duplication requirements, it was much simpler to run duplication R2R recorders at standard R2R speeds.
You seem to be saying the R2R speeds are based on the cassette speed. It would be the other way around. The Compact Cassette was invented in 1963, well after the R2R standard speeds had been established.
 
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Its interesting that mag tape chose to go down the powers-of-two route to speed standards and vinyl chose 78/45/33.3/16.7 rpm.
I looked into that recently, actually. The dude who built the first record player used whatever parts he had in his junk box. That happened to run at 78 RPM. 33.3 RPM is basically as slow as you can go while still have decent bandwidth. 33-1/3 was also chosen because it's easy to generate from a synchronous motor running 3600 RPM at 60 Hz. That's a gear ratio of 108:1. 45 RPM allows for better bandwidth and also a reasonable playing time.

Now we just need to figure out why 12" records recorded at 45 RPM are called half-speed recordings. :)

Tom