Magnetic Tape Harmonics / Modulation

[Brian Roth]

Geez....nothing much to add to this fracas besides:

http://mrltapes.com/scrape-flutter-and-tape-compliance-bibliography.pdf
Discussion about how tape "scrapes" across static surfaces and causes measurable/audible errors.

And Jay McKnight (RIP) was one of the original "rocket scientists" who investigated all this stuff decades ago when he worked at Ampex. Many of his other papers are "available somewhere" in the world. AES Journal??? He also closely studied the electromagnetic interaction of the recording head and the tape traveling past the head.

Bri

 

[gyraf]

..please avoid feeding the troll..

 

[Brian Roth]

..please avoid feeding the troll..

Point taken......

 

[abbey road d enfer]

I am actually challenging myself to look (and restrict) only into the magnetic process itself. Sorry, no time or occasion for more.

Just one tip, in case you had overlooked it. Bias oscillator phase and amplitude noise.

 

[kbx]

Please correct me if I've read this thread wrong...

but I find it baffling that anyone without an MRL tape (the most basic of agreed-upon alignment tools) would proclaim to be doing any sort of thorough scientific investigation of tape recording.

Not to mention- using old tape with sticky shed as part of their data.

Did I miss something?

 

[ruffrecords]

@kbx
to answer, I would need from you a bit more of details from your know how.

What is more precisely your concern with the non-MRL tapes (ex. LPR35) vs. my setup? Which tapes will fit?

I think he means an MRL test tape.

Cheers

Ian

 

[abbey road d enfer]

MRL stands for Magnetic Reference Labs; they are the most renown (may the only remaining) producer of reference (calibration) tapes.
Although I agree with many here that it is an essential element in calibrating a tape recorder for proper use and compatibility, I'm not convinced it is necessary for the subject you are studying. As long as your machine is capable of recording satisfactorily , i.e. with proper frequency response, decent S/N ratio and THD within tape limits, the time-variant effects should not be too different from a calibrated machine.

 

[Brian Roth]

IMHO (feeding a troll???) we need to establish operating levels before trying to look at any other various errors. Hence the reason for such things as MRL test tapes.

Standard operating levels are NOT solely intended to ensure interchange operating levels from one studio to another. At some point, electronics clip and heads saturate.

Flux loops can be helpful for analyzing errors within the electronics and tape head interfaces.

http://brianroth.com/library/flux.pdf
Bri

 

[abbey road d enfer]

At some point, electronics clip and heads saturate.

Tape saturates much before electronics or heads. Establishing a correct operating level can be done by observing the behaviour at HF. There is one point where level compression occurs, by the combined effects of magnetic saturation and self-erasing. Backing a few dB sets an acceptable operating level for the intended research.
Of course, it supposes a machine in reasonable working order.

 

[Brian Roth]

I agree that some tape formulations can "crash and burn" well before the electronics clip or the heads saturate. Newer tape can push the limits with older designs.....

How many dB above 185 nW/M will the electronics and heads operate in a linear fashion before adding signicant distortion along with tape saturation? I guess in a perfect world, those distortion elements would have been eradicated decades ago. Best of luck with an Ampex 350, or some older MCI's.

Bri

 

[gyraf]

I repeat: troll. Walks like a duck.. Etc.

 

[FIX]

I can still hear his voice... "250 nanowebers per meter". Fun fact:
They record the tones backwards so at the very start of the tone. it's dead on. Make sure you adjust by 2/3s of the way in...

 

[JohnRoberts]

Back in the mid-80s I was put in charge of Peavey's 4-track cassette program. I was forced to quickly learn how much I didn't know about magnetic tape. I am glad now to let that sleeping dog lie.

It is possible to recover from bad first impressions but first you need to realize you are making a bad impression. Everybody needs to try to be nice.

JR

 

[radardoug]

I see now, that presumably you expected me to read all the site, not just the page you linked.
Well, I am progressing through the website, but much slower.
I went through his flux-loop also quite fast. I am in a unique advantage here, since I have a calibrated loop flux. If I will ever need a design change, I am still being able to calibrate it up to +/-300G @ 5KHz to 150KHz range, with 0.01% precision (most readers will have here absolutely no idea how much R&D is behind this simple statement&capability). But I hope it will not be the case to need a new design.
Right now I am at 50% digesting his Intro, but I must stop - to get my sleep. Very interesting, but this alone took already more time than I planned. Maybe I continue tomorrow, maybe not.
So far, apparently Dale was successful to create a method and the device for rotational & repetitive scrap flutter, but his conviction&attempt to extend this to the friction (onto or between static elements) to solve all tape spectrum... was not so successful and put him actually up a wall. Maybe he had a unsuitable contact at the HP, back in those days they had the R&D dept concerning for these matters actually not in the US.

His unsuccessful attempt to use his device more than a QC "fingerprint" (pass/no pass) for non-rotational flutter or for tape characteristics, is worth to be noted. I am evaluating this exact door, but it is unclear at this moment how exactly. Proponents here for the W&F theory: are asked to have proofs which MUST lead to a method. But Dale did not have it. At least I did not get this Info with my reading at the current page.

There are statements in here that do not compute! First, you talk about your loop flux. I take it you mean flux loop.
You boast that you have a wonderfull flux loop calibrated to .01% from 5 kHz to 150 kHz. That wont be much use on a tape recorder, where the response is from 10 Hz to 20 kHz. Flux loops generally were used for specific purposes on tape recorders. They did not replace test tapes, which were always used as the primary level calibration. You make comments on Dale Manquen who you did not know. Dale was a giant in the field of analog tape. You comment that he had an unsuitable contact at HP. This shows how little you know of the history of tape recording. These gentlemen were on the bleeding edge of tape technology, and came up with many of the advancements in the science. Please put your ignorant scepticism away. Please do not post again until you have groundbreaking research RESULTS in a field that is now of only passing interest to most.
Since you are from Germany, I can understand you may have difficulties with English as a second language. But that does make it difficult for us to understand you.

 

[gamcneer]

I realize the following note is a bit off-topic, but I have a close acquaintance who figures prominently with Iron Mountain who has disclosed to me some MRL's that his company bought as being inconsistent. Check any purchases IMMEDIATELY after receiving them. Iron Mountain was given some runaround by the MRL people as they had not reported the problems soon enough.

 

[radardoug]

Test tapes need to be carefully looked after. If you had them for 6 months and then reported them, thats lots of time for bad storage to have an effect.

 

[gamcneer]

Test tapes need to be carefully looked after. If you had them for 6 months and then reported them, thats lots of time for bad storage to have an effect.

true. However, in the case I am describing, it was only a matter of days, not even a week

 

[Brian Roth]

I sincerely hope that after Jay McKnight retired (and recently passed away) his company (MRL) will still deliver high quality alignment tapes. Some of us still rely on the accuracy of those tapes.

Bri