cassette tape chicken vs. calibration egg?

[Mykle James Hansen]

Hi all,

Does anybody here possess a tape speed calibration cassette?
The kind that has a steady frequency on, usually 3000 or 3150 hz,
recorded with some fancy calibrated machine & certified to be
accurate within some small window of wow & flutter?

I just bought one. And it’s probably accurate … except that I just
played it in five different tape decks, and they’re all
playing it back more slowly than they should, by approximately
the same amount.

It seems unlikely that my fancy calibration tape I just ordered all the way
from Germany would be incorrect! OTOH it seems odd that all
five of my decks would be slow, rather than some slow & some fast.

Anyway if I’m anal enough to calibrate tape decks, I’m probably
anal enough to want to calibrate test tapes first ...
If my calibration tape matches someone else’s calibration tape,
I’d be more inclined to trust both of them. I can’t really
think of any other way to prove the accuracy.

-mykle-

[Jared Boone]

I don't know about you, or if this applies to mechanical devices, but I suspect it does: as I get older, the trend is inexorably toward running slower.

    - Jared

[Eric Garner]

if it's anything like my turntables, as the lubricant ages, it gets gummy and slows things down. 

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[Brian Richardson]

Seems like you could record a video of the tape playing with your phone and figure out the revolutions per minute and check to see if its going the correct speed? Or use a strobe light to dial in (like folks used to do with cars?)

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[Jared Boone]

Or for that matter, just compare the pitch of a track on a cassette that you can also stream or otherwise play back digitally. (still got a CD player?)

    - Jared

[Justin R. Miller]

On Jan 19, 2024, at 2:04 PM, Brian Richardson <ski...@knowhere.net> wrote:

> Seems like you could record a video of the tape playing with your phone and figure out the revolutions per minute and check to see if its going the correct speed? Or use a strobe light to dial in (like folks used to do with cars?)

If it’s helpful, you can borrow a timing light (along with many other tools) for free from FLAPS (friendly local auto parts store). It’s driven off of a signal from the #1 cylinder though, and via induction, which I bet you could replicate somehow at the revolutions you need. However this might be more of a project than you want to take on as it’s a pretty long yak shave.

I also like the idea of replicating the tone pitch. The command line tool ’sox’ is pretty great for this.

JM

[David Turnbull]

You can turn the magnetic flux directly into visible light then use a scale to check your calibration tape.

https://www.youtube.com/watch?v=aZOxn8ggX8w

https://store.arnoldmagnetics.com/product/284/magnetic-viewer-b-1022

Next you ask a machinist how to verify your scale.

https://en.wikipedia.org/wiki/There_Was_an_Old_Lady_Who_Swallowed_a_Fly

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[Dylan McNamee]

I'm surprised it doesn't have a click every minute or so -- absolute time is pretty easy to measure, especially at the macro-level. Other than that, the exact length of the tape, if provided, should give you a macro-measurement of tape speed. I have two Denon direct drive cassette decks which might be helpful for triangulation (and are probably in need of some calibration).

[Rob Wilcox]

All the kids are going digital now with the tapeless deck project:

https://www.youtube.com/c/TapelessDeckProject That person is in Poland, but I believe supports DIY. 

A long time ago, I worked in the high end recording studio of a famous music school. We had a library of tapes, and acetate disks of performances. They are all ProTools now. 

I need to transfer some 1/4 in tapes and retire my machine. There are some wacky audiophiles trying to being back reel-to-reel tapes. 

There is a guy in Vancouver BC who is making a good business restoring reel-to-reel machines. It is his second career, he retired from restoring CRT video projectors. You may have heard about him - Curt Palme. Now https://www.facebook.com/ReelToReelTapeRecorders. He is doing a good job restoring the last great tape machine the Ampex ATR series. 

To your original question, record a digital work of music into your DAW, play it out to record on your cassette tape, play it back into the Daw and time align a feature from the beginning and the end and see how far off they are. Similarly record a tone from the daw on the tape, then bring it back and use some analog tape cleanup software to study the flutter and wow.  

I see young friends doing cassette releases sometimes. 

Keep us posted on your analog adventures!

Rob

[Jerry Biehler]

You could make a reference tape with a function generator fed into the input of one of the other tape decks and compare them together. If they are all off by the same amount then something is up. Either that or find some way to put a tachometer on the capstan and see how fast it is running. 

-Jerry

On Jan 19, 2024, at 7:35 PM, Rob Wilcox <robwi...@gmail.com> wrote:

All the kids are going digital now with the tapeless deck project:

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[Loren M. Lang]

On Fri, Jan 19, 2024 at 02:31:02PM -0800, Justin R. Miller wrote:
> On Jan 19, 2024, at 2:04 PM, Brian Richardson <ski...@knowhere.net> wrote:
>
> > Seems like you could record a video of the tape playing with your phone and figure out the revolutions per minute and check to see if its going the correct speed? Or use a strobe light to dial in (like folks used to do with cars?)
>
>
> If it’s helpful, you can borrow a timing light (along with many other tools) for free from FLAPS (friendly local auto parts store). It’s driven off of a signal from the #1 cylinder though, and via induction, which I bet you could replicate somehow at the revolutions you need. However this might be more of a project than you want to take on as it’s a pretty long yak shave.

As I recall, the speed of the drive spindle for the take-up reel is
variable as the diameter of the reel increases over time. I believe
there's a separate motor inline with the read head that pulls the tape
through at a constant speed so that is what you need to measure. That
will be a little trickier, of course.

I'm actually not sure how they keep the tension constant on the tape
with that mechanism so now I am really curious how the whole mechanism
works.

>
> I also like the idea of replicating the tone pitch. The command line tool ’sox’ is pretty great for this.
>
> JM
>

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[Russell Senior]

There is a pinch roller near the read write head that maintains a constant tape speed. In theory, you could paint a dot on the pinch roller and count its revolutions over a given time period. Knowing the diameter would give you the tape speed.

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[Russell Senior]

Actually (clarification), it is the capstan that's driven, the pinch roller just holds the tape against the capstan.

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rus...@personaltelco.net

[Doug Ausmus]

The captain sets the speed past the head, the take-up and supply reels are design to operate such that they slip to create enough tension for a clean takeup. This slippage technique is a mechanical design element and was common for many mechanisms back in the day.

It is still used today in industry to control feed and take-up tension but with more modern methods such as a magnetic particle clutch.

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[Doug Ausmus]

Autocorrect: ... capstan... not captain... Ughh

[Jerry Biehler]

There is a slip brake/clutch on each pinion that applies a constant torque to the tape. 

-Jerry

On Mar 24, 2024, at 1:30 PM, Doug Ausmus <dau...@gmail.com> wrote:



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