Calibration tones on pre-recorded tapes?

[Fred Thal]

. . . The wider the track width and higher the tape speed, the greater the loss of HF when the repro azimuth is out of alignment.

Hello Charlie,

Thank you for posting. You're getting close, but not yet correct.

It's not the higher the tape speed, but lower the tape speed.

This is because a lower tape speed equates to shorter recorded wavelengths, which are proportionally more susceptible to azimuth losses for a given angle of mis-alignment.

Your observation about employing narrow tracks as a way around the problem is correct.

Here, we are trading away an optimum signal-to-noise-ratio (and other desirable attributes seen with wide tracks) for a format that better facilitates playback on inexpensive consumer and prosumer tape transports that exhibit poor dynamic azimuth stability.

What on earth could be "audiophile" or "high-end" about that approach?

Nothing.

I'm still waiting for a forum reader to show any interest in how the tape width (not the recorded track width) enters into the need for an azimuth alignment tone.

 

[topoxforddoc]

I'm still waiting for a forum reader to show any interest in how the tape width (not the recorded track width) enters into the need for an azimuth alignment tone.

Is that to do with "fringing"

 

[Fred Thal]

Is that to do with "fringing"

Well, a good guess Charlie. But no.

We see two types of fringing in analog audio magnetic recording:

Fringing of the generated flux field seen at the record head gap. More specifically, flux field lines in the free space out in front of the gap. (Relates to how and where recording actually takes place.)

And, fringing at the reproduce head gap. (This latter one is what tape users usually mean by the term fringing.) This fringing is caused by the presence of long recorded wavelengths on any tape having recorded tracks that are wider than the tracks on the reproducing head. This condition is the case seen with the common reproducer alignment or calibration tapes that are full-tape width recorded and not fringing compensated.

But all this has nothing to do with our investigation into how and why tape width plays a role in azimuth errors introduced with tape interchange between machines.

 

[Fred Thal]

Tired yet?

Ok, before everyone tunes out this thread permanently, maybe it's time to offer some clues.

First, here's question two again: How wide is quarter-inch tape and why does this matter?

Now the clues, again presented as questions. The first one contains the biggest clue.

What is the commonly seen range of quarter-inch tape width?

How does the force-guidance headblock design of the Ampex ATR-102 work?

What happens to the geometry of the ATR headblock's reverse-camber path arc, when a slightly narrower (or wider) tape stock transits through it?

(This is very relevant to our discussion, as we see this popular professional model Ampex recorder in wide use by many of the major pre-recorded tape producers today.)

 

[topoxforddoc]

Is it to do with whether the tape is slitted as imperial (1/4 inch) or metric (6.3mm).

Charlie

 

[Fred Thal]

Is it to do with whether the tape is slitted as imperial (1/4 inch) or metric (6.3mm).

Charlie

Sorry, no.

It's not about metric or Imperial measure.

We accept that the range of actual width on nominal quarter-inch tape is from about 6.20 to 6.29 mm.

But it's up to the individual manufacturer to decide what passes their final quality control (QC), or not.

Slitting accuracy was always a huge QC problem for the tape industry here in the USA.

Turns out it's very hard to control, very, very hard to do.

Only Agfa and BASF in Germany were ever able to do it right, consistently, and today they are both long out of the tape business.

 

[c1ferrari]

Very good read, here: http://thehistoryofrecording.com/Papers/Jay_McKnight/Azimuth_in-a_Magnetic_Tape_Recorder.pdf

 

[c1ferrari]

Slitting accuracy was always a huge QC problem for the tape industry here in the USA.

Turns out it's very hard to control, very, very hard to do.

Only Agfa and BASF in Germany were ever able to do it right, consistently, and today they are both long out of the tape business.

This is EXTREMELY frustrating...RTM -- champion our cause!
Here's an explanation of analog audio tape manufacture: http://www.recordingthemasters.com/thefactory/

 

[topoxforddoc]

First, here's question two again: How wide is quarter-inch tape and why does this matter?

Now the clues, again presented as questions. The first one contains the biggest clue.

Fred

Is this to do with the fact that the McKnight AES paper (linked above by Sam) discusses how the tape path for 1/4 inch tape can vary by a tiny amount, and that this might affect the repro head azimuth? Hence, you need the line up tones on each tape, so that the repro head can be lined up for each pass.

"Finally, an effect that we have observed on 6.3 mm width tapes, but have not seen on wider tapes: Suppose that we record a tone on a tape, then cut it into two pieces. The azimuth on both measures the same, as it should. We put one aside, and we use the other about twice a day to set azimuth on our tape transport. After a month or two we compare the azimuth on the used tape and the set-aside tape, and find that the azimuth is considerably different (sorry—don’t have a value at hand).
We do not know in what way the tape has changed to cause this effect, but it happens repeatedly."

Charlie

 

[Fred Thal]

. . . the tape path for 1/4 inch tape can vary by a tiny amount, and that this might affect the repro head azimuth? Hence, you need the line up tones on each tape, so that the repro head can be lined up for each pass.

Yes.

But, rather than saying "might affect" you could better say "does affect".

If you study different headblock (and tape transport) architectures (we have many), comparing how those different headblock designs handle differing tape widths (meaning tape widths differing by only one or two thousandths of an inch) you'll quickly appreciate why repro head azimuth absolutely needs to be adjustable for the playback of all tapes.

Anyone asserting that this is not the case is misinformed, if not purposefully misleading you.

Also Charlie, one should not need to adjust the repro head azimuth on each pass, if it's the same tape playback equipment being used. That said, if you instead find that this adjustment is needed with each pass, then you have a hardware problem.

We should re-group now, returning the point of this thread to emphasizing that putting a smart azimuth alignment tone at the head of any pre-recorded tape that purports to be "audiophile grade" ought to be mandatory.

Eight seconds of such a smart tone would probably suffice. Anyone not wanting to bother with it would be free to ignore it. So why aren't the tape producers doing this?