How to make a Speed Calibration tape

[Dr ZEE]

I agree...but I'm asking, how would you know if you have acceptable stablity.
?

Well, I guess first one need to define "acceptable".
You can "observe" and raughly estimate the "speed instability" of a machine by recording a tone or puls, then play it back and "compare" with the source.
This will "show" the instability of the "second generation"

Ideal situation, of course, for precise estimation of "speed instability" would be to (already) have the tape that is magicly PERFECTLY pre-recorded with a PERFECT puls, which would require a PERFECT generator and a perfect recorder-machine, which of course exist only at MRL, and only GOD knows how MRL guys estimate the speed stability of their machine.

Firms like to use terms like "Laser Precision" in their adds , it works wonders

MRL provides STANDARDS (and the ONLY standards) not because it is so, but because WE all AGREED that it is so. And that's just the way it is

 

[miroslav]

And on playback we get:

11121222322211234322221111 Left sync head
-----11121222322211234322221111 Right playback head (offset in time)

Now we see differences in the frequency between the channels.

Yes...I understand sync/PB head operations....

But if the tape speed changes...will it not change simultaneously for both sync and PB head locations?
So therefore...will not the "beat"/offset remain the same (even with change)?

The reason I asked about using source VS playback because then you would have one steady/stable signal against a moving one (PB)...and if the tape fluctuates in speed, then the beat changes against the steady/stable one.

 

[miroslav]

... and only GOD knows how MRL guys estimate the speed stability of their machine.

For their speed tapes...they claim it's .05% of true wavelength (and that's only due to tape stretch and tension).



I'm not GOD...I just read their PDF.

 

[evm1024]

Yes...I understand sync/PB head operations....

But if the tape speed changes...will it not change simultaneously for both sync and PB head locations?
So therefore...will not the "beat"/offset remain the same (even with change)?

The reason I asked about using source VS playback because then you would have one steady/stable signal against a moving one (PB)...and if the tape fluctuates in speed, then the beat changes against the steady/stable one.

If you have a stable oscillator you can use that....

On record we get speed differences but no phase changes. On playback (within the same head) we get further speed changes but no phase changes. The speed changes track.

When using different heads per channel the speed changes the playback equally but the speeds recorded on the 2 tracks differ which results in a phase change.

When the numbers in the graphs are the same (left ch to right ch) we have no phase change even tho the frequency changes. When we have different numbers left ch to right ch we have a phase change that tells us that the tracks are not stable in frequency and thus speed.

Regards, ethan

 

[evm1024]

For their speed tapes...they claim it's .05% of true wavelength (and that's only due to tape stretch and tension).



I'm not GOD...I just read their PDF.

You know Jay is quite approachable. We have exchanged emails a few times. I do wonder who will pick up MRL production when he retires.

--Ethan

 

[Dr ZEE]

...I was just throwing a little fun into the discussion.
....

humor is essential.
Just imagin Ethan's serious and focused face while he's cutting precisely 25 feet of tape using his trusted wooden tool ...heh heh

Ethan, I demend a photo!

 

[evm1024]

humor is essential.
Just imagin Ethan's serious and focused face while he's cutting precisely 25 feet of tape using his trusted wooden tool ...heh heh

Ethan, I demend a photo!

Soon, I have to try this out, and I want a calibration tape.

Sadly (well not really as that we are in for some fun) we are in cruise season and I head down to newport tomorrow (hear that Beats!) to inspect one of the research ships we will be using in the next 3 weeks. I'm going to try to extend the WiFi range offshore (we have hit a ship at 40 NM before!) for this cruise.

Also, I'm working on setting up VOIP phones to the research scientests can talk ship to ship offshore (read out of cell phone range) to coordinate activities without running up to the bridge and using the VHF.

The short explanation is that time is very short for the next few weeks.

--Ethan

 

[Dr ZEE]

.. time is very short ...

--Ethan

Time is non-existing, yet convenient notion

 

[evm1024]

Time is non-existing, yet convenient notion

There is no spoon

 

[Dr ZEE]

There is no spoon

true.

 

[miroslav]

When using different heads per channel the speed changes the playback equally but the speeds recorded on the 2 tracks differ which results in a phase change.

The part I'm not seeing is what do they differ from...each other? What is the reference point that they are differing from?
It makes sense that as your speed changes the playback from *both* Sync and PB heads will change...but it changes equally, so how will the outputs differ/change relative to each other?
The change happens simultaneously at both heads, right...so while the overall playback changes as speed varies, how are you using the two heads to establish any differences in their initial offset?

Example (as I’m seeing it):
You and I are on a treadmill at the airport and you are standing 3 feet in front of me.
They vary the speed of the treadmill, but you and I always remain 3 feet apart, and our speed changes simultaneously as they vary the speed.
So what is the reference point if both points are moving/varying simultaneously while always maintaining the same distance/offset from each other?

That’s what I’m stuck on…

You know Jay is quite approachable. We have exchanged emails a few times. I do wonder who will pick up MRL production when he retires.

Yeah, I had some email exchanges with him recently about one of my test tapes, as I was hearing some print-through and wanted to check with him how much was acceptable.
Yes...he was easy to communicate with and was generally friendly and sincere in his concerns.

 

[evm1024]

The diagram shows it all....

Changes in speed on playback are irrelevant for the reasons you stated.

Changes in speed on record print to both tracks at the same time.

On playback using 2 heads the sync head and playback head see the tape at the same speed. However, the sync head reproduces the signal at record time T and the playback head reproduced the signal at time T+n where n equals the time between the sync head and the playback head.

Speed changes occur over time. So at record time T the speed is 15.00 isp and at time T+n the record speed is 15.01 ips.

Because any speed changes on playback happen equally to the sync and playback heads they factor out to 0 but the phase difference between the 2 heads changes in proportion to the speed changes during record.

I can't be more clearer than this. The diagram does show the differences between channels quite well. 1 represents some speed, 2 another speed and so on. Where there are differences in speed between the 2 tracks we get a difference signal. If there was no speed difference there would be no difference between any point on tape.

Regards, ethan

 

[Dr ZEE]

(if I cared! )... To "observe" tape speed instability I would just record tone and play it back and "watch it" in one form or the other on a device that can "show it" in one form or the other , taken from a single track of a single head. It will be what I've called "second generation" "instability", double trouble with a twist, that is ...heh heh

Here's (actually was) a 50 bucks "tape speed instability quantizer / observer" , and nobody cared : http://cgi.ebay.com/Leader-LFM-39-A-Wow-Flutter-Drift-Meter-Unused_W0QQitemZ380146377418, "super-stable" oscillator output on the back is provided

 

[Beck]

Tim, the point here is that to calibrate tape speed you DO NOT NEED to have a special "reference" tone that (as we MUST trust, of course ) is super accurate and was recorded at super accurate and super stable speed.

But! you do need a good (stable) tone (or puls) generator and an accurate counter. And, yes, the machine you record the tone/puls on should have 'acceptable' speed stability.

BTW, MRL is a real great "entity", but it's also a business The things that MRL sells are not gifts from God, you know, those things were actually "made". But, then, of course, only guys at MRL with their out of this world machines and with their knowledge and wisdom can do this. Of course!!!!

Sure Mike, I understand what you’re saying and I think this sort of endeavor can be a lot fun as well as productive. I like Ethan’s initial idea… he’s always thinking.

First, a little about MRL and standards in general. Thank God we have MRL. There used to be others that made calibration tapes, like Ampex, BASF, STL, Nortronics, etc. MRL is the last one standing.

It’s inevitable that standards will go by the wayside, as we get further away from the “Analog days”. So I guess you can always count on me to be the voice of orthodoxy it matters such as this. MRL does what it does very well, and the machines are highly accurate and meticulously maintained. Everything has to be as smooth as possible. Things like tape thickness and tape tension will impact tape speed and thus the accuracy of the tape. McKnight is a treasure. He’s not just a businessman, but also a pioneer that has poured himself into research and advancement of tape recording technology for decades. He’s a visionary and someone I admire very much. I’ve spoken to him myself several times over the years. He’s a great guy. So, we don’t have to dismiss MRL to pursue our experiments. Let’s keep those issues separate.

Back to standards… Ok, so maybe I put the anal in analog, but somebody has to. I was saying before that I think it’s even more important now that we agree on time-honored standards and we would do a disservice to neophytes if that’s not the first thing we introduce them to. Compatibility between like formats will always be important. That’s all I’m saying. If everyone is doing their own thing with varying degrees of success it will be just one more little thing that will make tape a less viable option. Meaning, if those of us that are now in charge of the Good Ship Analog aren’t worthy sailors we may run this baby into the rocks and sink this thing once and for all. I’d hate my name to be listed on that crew sheet.

As for experimentation… cool! There are a lot of reasons to be part of this forum and we can all learn from each other. Myself? I’m primarily an artist… songwriter, musician, and recordist who just happens to have a high technical aptitude when it comes to the devices and mechanisms that I use. I do all my own calibration and have modified half of what’s sitting in my studio. And what I can’t find, I invent and build myself. So I certainly understand the desire to find other ways to do things. In this particular case I say what I’ve always said… “Every serious recordist needs to get a calibration tape for each format.”

Other than that I too like messing around with this stuff but I find it distracts me from writing songs, so I plop down the money for the MRL tape. And now I have one and we're done.

I read over the thread again. So I have a couple questions. In Ethan’s original brainstorming where is the initial frequency going to come from? What do you mean by pulse? what will it be in kHz? and will it be recorded using the deck of which the current speed is an unknown? Just trying to make sure I have the right picture.

~Tim

 

[miroslav]

Because any speed changes on playback happen equally to the sync and playback heads they factor out to 0 but the phase difference between the 2 heads changes in proportion to the speed changes during record.

"...during record."

OK...I think I get now how you are saying it.

The way I was reading it before was that you would first Record...then rewind...and then hit Playback and do your tests/measurements using both Sync & PB heads during playback.

But now I see that you are actually staying in Record and then just monitoring from the Sync and PB heads for your measurements...is that what you are saying?

See...on my Otari 2-track, the Sel-Rep and Source/Monitor thing works just a little differently than it does on my 16-track, so the whole time I was thinking you were always talking about doing the measurements in playback mode, not in record mode....which made me wonder how the offset was going to change for one head and not the other.
But in Record mode with both Sync and PB head monitoring...yeah, OK.

 

[evm1024]

SNIP!


I read over the thread again. So I have a couple questions. In Ethan’s original brainstorming where is the initial frequency going to come from? What do you mean by pulse? what will it be in kHz? and will it be recorded using the deck of which the current speed is an unknown? Just trying to make sure I have the right picture.

~Tim

The original sine wave signal can be any frequency. I picked 1 KHz. It is of unknown accuracy but is presumed to be somewhat stable.

The term pulse is used to represent 1 cycle of that original sine wave.

Any deck can be used to record that sine wave. The decks speed is unknown but the wow and flutter are presumed to be less than 1% (ie not obviously audable)

The tape is a known length. By cutting a fixed length of tape and putting leader on it we have defined one of our references to the accuracy of our length measurement.

A counter in total mode will count each and every cycle.

Run the tape on ay deck with the counter hooked up and we get the number of cycles on that length of tape. Run it at any speed, we don't care. The counter is only counting cycles.

With a known length and known cycle count we have all that is needed to calculate the frequency of the recorded signal at our target tape speed (or any other tape speed).

IN the example given in the beginning of this thread, 25' of tape with 20,000 cycles on it yields 1 KHz when your deck is going 15 ips.
25' = 300"
300" / 15ips = 20 sec
20,000 cycles / 20 sec = 1 KHz

If you counted 19,500 cycles then

19,500 / 20 sec = 975 Hz

This is now your target calibration frequency for setting speed....

Regards, Ethan

 

[evm1024]

"...during record."

OK...I think I get now how you are saying it.

The way I was reading it before was that you would first Record...then rewind...and then hit Playback and do your tests/measurements using both Sync & PB heads during playback.

But now I see that you are actually staying in Record and then just monitoring from the Sync and PB heads for your measurements...is that what you are saying?

See...on my Otari 2-track, the Sel-Rep and Source/Monitor thing works just a little differently than it does on my 16-track, so the whole time I was thinking you were always talking about doing the measurements in playback mode, not in record mode....which made me wonder how the offset was going to change for one head and not the other.
But in Record mode with both Sync and PB head monitoring...yeah, OK.

Nope, not staying in record. Your first understanding was correct. We record and then play back.

--Ethan

 

[miroslav]

OK...now I think I finally understand what you are saying.

There are going to be phase differences during record AND playback if the deck speed is unstable...
...so then the phase differences that were *recorded* will vary from the phase differences during *playback* because the instablity of the deck will never be the same way both times.

Is that what you are saying?

 

[Dr ZEE]

..to Tim Beck!

Heh heh.

On subject of "business".

One thing I'd need to clear up a bit for the "record" ... In my mind "business" (in general) is NOT a negative (pejorative) term.
Business = Good! (in general, that is).
Then there are all kind of businesses, but that would be a separate topic.

Honestly, I personally think that MRL tapes are too cheap. And I am not kidding. If I was doing what they do - I would not do this stuff for nothing and would not do this for a little nor for just "O.K. cash".

And when "good guys" run a business - even MORE power to them and it's all good for everyone at the end.
But it is what it is.
************


On subject of standards

Tim! You see we are "dealing" with speed here, distance unit per time unit that is.
So?
The only two standards are needed:
1. 1 inch (or meter) (distance unit)
2. 1 sec (time unit)

Last time I've checked Magneting Rec. Lab kind of was not in Time and Space business... or did I miss something ? heh heh

You see , when you use MRL "speed calibration" tape, you are not matching speed by measuring the actual speed of tape on your machine, but instead you are "matching" speed of tape on your machine to speed of tape on MRL's machine. Which is fine. It makes practical sense at the end. Or does it?
At the end it's not about 15ips, but insead, it's all about WhatEver-MRL-machine-ips.
As long as we ALL agree that MRL's machine is STANDARD, then we are all happy cats ..heh heh heh , as all we really asking for is to get "standardised" .

Or you can do it without MRL, all you need to do is to find the way to actually measure the "actual" speed of tape on your deck.

So, again, Ethan's "idea" is all about figuring out the period of recorded tone(or puls) on tape. If you know the distance between periodic waves/pulses on tape (or total amount of periodic waves/pulses per known length of tape), then your frequency counter can be used as speedometer.

 

[Muckelroy]

Or you could locate a MRL test tape, play back a known frequency, and have somebody with perfect pitch listen to it and tell you which way to adjust your speed