Setting repro head azimuth on your playback transport

Fred Thal

[Industry Expert]
Jul 15, 2016
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For introduction of this topic, please consider three questions:

What could support the view that setting repro head azimuth for optimal playback is not necessary?

Which pre-recorded tape producers are putting azimuth alignment tones on their tapes?

How should one set the playback head azimuth when there is no azimuth alignment tone on the tape?

Responses invited.

Thanks.
 

topoxforddoc

Well-Known Member
Feb 20, 2015
67
6
138
Cheltenham, UK
For introduction of this topic, please consider three questions:

What could support the view that setting repro head azimuth for optimal playback is not necessary?

Which pre-recorded tape producers are putting azimuth alignment tones on their tapes?

How should one set the playback head azimuth when there is no azimuth alignment tone on the tape?

Responses invited.

Thanks.

Fred,

This is my view, but I got taught by an ex BBC Broadcast engineer, who then worked at the British Film Institute restoring film soundtracks and old videos/films. Sadly Stewart Emmings, my mentor, passed away a month ago at the age of 49.

1) Line up tones are absolutely necessary if you are going to get the best out of your tape. I routinely check the repro level on both channels and replay azimuth on various distribution masters and safety copies using twin PPM meters with a mono/sum function. On my two Sony APR5000 machines, I adjust the test tone repro levels on the fly using the software driven menu. In fact, the TSL AMUT-2MA PPM meter unit I use also has an azimuth meter incorporated. The other way to do this is with a scope using X-Y Lissajous. (Of course, when checking all of my masters with my PPM unit, I have found that the replay azimuth has not needed adjustment - that's what you would expect from a properly recorded tape)

2) No idea about current producers. I know that my Tape Project tapes have no line up tones. Personally I can't understand why current producers don't routinely put line up tones on all of their output - may just be a workload issue. All of my old "master tapes" have tones however. These are all duplicated (with new 1k, 10k, 100 & 15k line up tones) onto modern tape stock on receipt after adjusting the reproducer repro levels and replay azimuth using my PPM meters, before transfer to another properly lined up Sony APR5000.

3) Tough question - you just have to assume that the tape has been recorded correctly on a properly adjusted machine. When there are no tones, I set my machine up for repro level and replay azimuth using a standard test tape and hope that the machine the tape was recorded on was set up properly too.

Charlie
 
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Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
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Thanks for replying, topoxforddoc.

I get asked if there's really an analog tape revival underway today. Is it a novelty for people who think tape machines look cool and are fun to display and use?

Or, is it for people who believe that the main problem with tape machines (and pre-recorded tapes) fidelity was only the playback electronics, so that all you need for reaching analog audio nirvana is adding a new outboard tape stage? (But what about all the time-base smearing from the tape transports and tape replication?)

Or, is it about a small, elite sub-set within the ultra-high-end analog community, where people are willing to go to extremes for achieving the highest possible playback quality? Even if it means acquiring real master tapes?

If it's the latter, that could be interesting. But today's tape renaissance is likely destined for failure in the high-end segment if the persons promoting it try to downplay or hide the fact that optimum tape playback is hardly trivial.

Bottom line is that some real effort is required to understand analog tape. There's an undeniable need for education. Of course, the student must first be eager for that knowledge. It's not a good sign when we have people selling purportedly reference grade "master tape copies" that have no meaningful alignment tones on them.

We accept that not everyone is receptive to being informed that they are overlooking something. Imagine how some of the pros inside the record labels bristle at the notion that they might not know how to properly play back a master tape! But after 35 years of observing them, that's been our conclusion at Audio Transfer Lab. Sadly. By the way, just how badly the analog master tape to digital transfers were done by most record labels remains an under-reported scandal.

Here then, for any interested WBF readers, is a shortened form of how it needs to be done, when you are serious about recapturing the audio program residing on a master tape in the highest quality.

How to play back an analog master tape in seven steps (Courtesy of Audio Transfer Laboratory):

Step one: Identify the tape width and the recorded track dimensions
Step two: Install a read-only headblock exactly matching the above parameters on the reproducer
Step three: Set the reproducer's tape tensions according to tape's base film type
Step four: Identify the recorded tape speed and equalization
Step five: Set the reproducer's tape speed and the playback amplifier's equalization to match the above parameters
Step six: Adjust the repro head azimuth to the calibration tone or recorded program
Step seven: If additional calibrations tones are present, fine-adjust the playback amplifier for flat overall response of the recorded program
 

topoxforddoc

Well-Known Member
Feb 20, 2015
67
6
138
Cheltenham, UK
Hi Fred,

I have only been in this game for about 2 years, but it's amazing how much you can learn. Sadly my mentor passed away a month ago, but I think of him every time I line up another tape on my machines.

Now I understand the basics, I can see why optimising everything is the key to getting the absolute best out of this great medium. I can't see how fancy replay electronics can come before understanding basics about how analogue tape works and how to line up your machine. Maybe it's just because people are frightened at the thought of adjusting everything on a pro studio machine. A nice glitzy consumer/prosumer machine looks manageable, just like a cassette deck. But of course, few cassette decks get the very best out of that medium, but some do, like the high end Naks, where you can adjust the azimuth and calibration.

The problem about many consumer decks is that access to calibration controls is sometimes difficult. Also, most consumer machines have only one "memory" setting i.e. the one you have just made with your tweaker. Hence, there may not be much appetite to learn as it's just too much fuss.

Using the Sony APR5003 has been a dream in terms of learning, as everything is software driven off the front panel. The huge printed manual is great; if you don't have it, you can download it from Richard Hess' APR website.

I haven't needed a huge amount of kit to get going - a test tape, calibrated test tones, an XLR-RCA balanced transformer and my TSL PPM unit with mono/sum function (or an oscilloscope if you just have standard PPMs without twin needles or mono/sum). Once you have learnt how to do it, it just becomes second nature. With the high cost of master tapes and new pancakes (I'm in your small elite sub-set here), it seems daft not to try and get the very best out of it. It's no different to guys spending ages on setting up a cartridge for vinyl replay.

Charlie
 

stellavox

Well-Known Member
Apr 23, 2010
284
61
1,583
For introduction of this topic, please consider three questions:

What could support the view that setting repro head azimuth for optimal playback is not necessary?

Which pre-recorded tape producers are putting azimuth alignment tones on their tapes?

How should one set the playback head azimuth when there is no azimuth alignment tone on the tape?

Responses invited.

Thanks.

Fred,

I don't understand where you are "coming from" with this post, especially when I read your followup comments. You ask one set of questions originally, then launch into what I view as various criticisms of the "tape revival" in your subsequent posts.

Let's take your original post first; I doubt that anyone who is taking part in this current revival and had done their homework would argue that head azimuth is NOT important. HOWEVER, on most of the machines I have ever worked on, the azimuth, once set "properly" (I use the Sound Technology "technique" with the special tone sequence) stays put unless the machine is "severely disturbed" - let's say dropped. When I discuss the transport situation with the most of the folks I deal with (that use my tape preamp), they have used a "competent" technician to set up their deck and azimuth is of course one of the things that gets checked and set "correctly". SO I would opine that there is no need for the folks supplying prerecorded media to put an azimuth tone on the tape. I do appreciate those who do put a 1Khz tone at the beginning.

To reply to your second post; yeah, I have listened to a LOT of different decks, and A/B'd their "sound" using stock electronics and the heads wired out outboard electronics and found that from what I will call an "audiophile perspective, the STOCK repro electronics on most decks is the major impediment to really good sound. And my opinion is not alone; there are maybe a half-dozen folks supplying outboard tape repros and someone is buying their product. I'd suggest eliciting opinions from others on this forum, especially those who have outboard electronics and a switch installed on their transport to allow the head output to be switched between outboard and the "stock electronics, as to why they did it and what the results were/are. As an aside, I've also had and taken the opportunity to listen between 2 track repro HEADS from different manufacturers and heard differences there also.

Charles
 
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topoxforddoc

Well-Known Member
Feb 20, 2015
67
6
138
Cheltenham, UK
I think that Fred is trying to ask how many people assume that the tape they're playing has been recorded perfectly and still in optimal condition. The point is that not every tape you play is going to be optimal. I have certainly had original distribution master tapes, where I have had to adjust things on the repro side before playing and duplicating the tape onto new stock.

Whilst I haven't had any yet where the repro azimuth needs changing to suit the tape, I have certainly had several tapes, where the line up tones at the head don't read at PPM4 on both channels. Sometimes, you can find that the HF line up tones are down as well on older masters. If you just play the tape as is, with no repro adjustment, the tape will not sound at its best. However, alter the repro levels so that the line up tones are matched with a flat frequency response, and hey bingo, suddenly the slightly disappointing purchase comes to life.

Azimuth repro head adjustment is just another part of optimising replay, when playing or transferring older tapes. To be honest, getting this whole business right normally doesn't take me more that 5-10 minutes with the right equipment. But this is no different to making sure that your cartridge is perfectly aligned with correct VTA, VTF and azimuth on your turntable. Get that wrong and no high end phono preamp will rescue the signal from a badly adjusted phono cartridge.

2 years ago, I would just have been completely flummoxed by it all. But now I understand, it seems crazy not to try and get the best out of my very expensive master tapes.

Charlie
 

Ron Resnick

Site Co-Owner, Administrator
Jan 24, 2015
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Thank you, Fred, for starting this interesting thread!
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
The three questions presented at the beginning of this thread were intended to provoke thought about what's going on with the azimuth adjustment on tape playback and also to draw attention to the curious fact that many (most?) providers of pre-recorded tape copies are not putting useful alignment tones on their products.

For the benefit of any readers not familiar with the professional analog tape world, here are a few additional points:

Copies made from master tapes should not be called master tapes, as obviously they are only copies.

It can get confusing. For example if you go down a generation (or more) from a master tape, perhaps to add equalization specific for vinyl mastering, then that resulting tape product might be called an eq master.

Back in the day, any master tape that did not have a series of alignment tones at the head, was considered a technically sub-standard product. In other words, it was by definition not a professionally made product. The debate back then was not about whether or not there should be alignment tones on master reels, but rather about how many (different) such tones were desired.

Aligning a reproducer to the recorded azimuth of any given tape was (and is!) considered a fundamental requirement in the professional world.

Take a look at any professional reproducer (a reproducer is the technical name for a tape playback transport). Notice the calibrated azimuth adjuster knob, with a calibrated scale on the headblock at the repro head. This adjuster is there because a given tape will often travel a different path through different tape transports and their headblocks.

Hope as we may, we actually have almost no basis for any confidence that the transport which made a given tape also recorded that tape with an azimuth alignment that will somehow exactly match a fixed reference setting on our playback machine.

Anyone doubting the need for analog tape playback azimuth adjustment might do well to ask a reputable vinyl mastering engineer having deep experience cutting from tape.

Placing a 1 kHz tone on a 15 in/s tape is hardly useful for the purpose of adjusting azimuth on the playback machine.

If a pre-recorded tape maker is willing to devote 25s of time to calibration tones, that would be wonderful, but filling that block with only a 1 kHz tone is tantamount to being brain-dead. In my opinion, somebody needs to learn a lot more about optimal analog tape replication or hire a qualified consultant for help with this.

Azimuth adjustment on a tape playback machine (again, such a machine is technically called a reproducer) is not an issue of the mechanical stability of the head mounting in the headblock. It is one of facilitating proper tape interchange.

In other words, it's about adjusting the repro head azimuth to a given pre-recorded tape in question, so that the frequency response on playback will be correct.

Not understanding the result of misaligned repro head azimuth with respect to a given recorded tape invites some serious undesirable consequences for the end user.

Again, can we take this tape renaissance seriously? Or do the purveyors of pre-recorded tapes see it only as a novelty market?
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
For anyone who has been left in the dark wondering, I now see that we've overlooked explaining what happens when the repro azimuth is not correct. Sorry!

In analog magnetic tape, azimuth is a mechanical alignment concerning the repro head gap's orientation relative to the recorded signal (the magnetized domains) on any given tape.

When the azimuth alignment is wrong, the result is a drooping frequency response. The high frequencies affected by azimuth misalignment will not be reproduced correctly. They will be attenuated, oftentimes severely so. The response losses due to azimuth misalignment in analog tape reproduction are not directly recoverable.

In practical terms: if a recorded tape sounds "dull" (no highs) always suspect azimuth misalignment first!
 
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Tapetech

Well-Known Member
Apr 10, 2014
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Fairfax, VA
I believe that azimuth error is not going to be a serious problem for the great majority of today's participants in this new "tape revival". Reason being is that most of these participants are using recently restored tape decks with new or relapped heads which have been azimuth adjusted with MLR tapes. Same can be said for the pre-recorded tapes these same people are buying: These tapes have been recently recorded on fully (and recently) refurbished tape decks. The heads are typically new Flux Magnetic heads and the azimuth has been adjusted with MRL tapes. Given this scenario, I think typical azimuth errors encountered are going to be quite small.

I also think it may not be a good idea for your typical audiophile to be messing with head adjustment screws. Test equipment is also a consideration: the vast majority of audiophiles do not own dual-trace oscilloscopes (with are needed to properly align play head azimuth).

If an audiophile has a recently refurbished deck and buys tapes from quality, known sources, then azimuth errors will be very small and not be a big factor in replay quality.

I thinks play EQ errors could be a larger factor (than azimuth) for new participants in today's "tape revival". If one buys a tape preamp and connects it to a tape deck that has a "head output", errors in play EQ could and probably do happen. The tape preamp EQ needs to be adjusted for that particular head and most audiophile that use separate tape preamps don't do that (tune their preamp frequency response for the particular head with an MRL test tape).

Buying a turn-key tape deck "package" (with built-in or separate preamps) that has been fully tuned by a professional with an MRL tape is the solution to the above problem.
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
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. . . the vast majority of audiophiles do not own dual-trace oscilloscopes (with are needed to properly align play head azimuth).

No, that's not correct.

You do NOT need a dual-trace oscilloscope to adjust repro head azimuth.

Although the 2-channel oscilloscope application recommendation has widely appeared in many tape recorder technical manuals, and although it can (with a full width recorded azimuth alignment tape) effectively bring a two-track repro head into an azimuth alignment where the head's two gaps are nominally co-linear (for inter-channel phase matching) it was never technically correct.

For example, how could this 2-channel scope technique ever work for a full-track monaural repro head?

The only technically correct definition of optimum repro head azimuth alignment is this:

That setting which gives the peak short recorded wavelength response (essentially, this means the peak high frequency response) for a recorded track under consideration.

Importantly, this response amplitude peak is easily seen with a simple VU meter, or with an audio frequency AC millivoltmeter.

Whereas a Lissajous pattern displayed on a 2-channel scope only shows you the relative phase relationship of two channels.

Misunderstanding or overlooking the subtleties of this distinction can easily lead to sub-optimum analog tape playback. A full classroom day is devoted to understanding and performing azimuth alignment on reproducers in our professional operator training classes.

Lastly, I think your blanket confidence in the technical competence of all the tape copy makers now on the scene with respect to such things as record azimuth alignment precision might be misplaced. Of course, if the tape copy makers would only now include meaningful alignment tones on their tapes, we could easily verify this and also be able to optimize playback with any reproducer, including prosumer and consumer machines, many of which have never enjoyed reputations for azimuth accuracy.
 

stellavox

Well-Known Member
Apr 23, 2010
284
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1,583
Fred,

I can't agree with your assertion that "inter-channel phase matching" is not important - especially in multi-channel recordings.

Let's try this: What if we have a 2 track "original" made on a machine with "correct" azimuth, and play it back on another machine that has it's (inter-channel) azimuth "off", so that the phase of (let's say) the left channel slightly leads the right channel. When I compare the dub to the original, won't I HEAR that the imaging is "off" somehow - not as precise - maybe "smeared"? Especially on an orchestral recording in a good hall with its added ambient clues, so that there is a "LOT GOING ON" within the soundstage, not just in amplitude and frequency but also in TIME? And as you add tracks, especially up to 24, I would opine that the "smearing" of a "mis-azimuthed" head on another machine would have to be greatly exaggerated.

Are you aware of anyone having tried this (say rocking the azimuth of the PB head slightly back and forth) and reported on the AUDIBLE EFFECTS?

I have NOT tried this but have an intuitive feeling that inter-channel phase matching is VERY important for FAITHFULLY reproducing the IMAGING of the SOUND on the original tape. Am I missing here - are the audible effects of these phase differences so small as to be inaudible??

THANKS

Charles

ps If I'm making any kind of a coherent argument for phase matching, then using a two-channel scope to observe /set it can work just fine.
 
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Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
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Fred, I can't agree with your assertion that "inter-channel phase matching" is not important -

Nowhere did I assert that.

Please re-read my post and see that the point under discussion there was that optimum azimuth and inter-channel phase matching are actually two distinctly different matters.

Of course, my protests about using only correct terminology often fall on deaf ears. It's not helpful that many mastering engineers have long conflated the terms "phase shift" with "azimuth error". Cedar's digital "azimuth corrector" product is a good example how this misunderstanding perpetuates itself.

This is part of the story of why so many of the analog master tape to digital file transfers have been quality-compromised.

We try to show mastering engineers who are working with analog tape that correcting for phase shift is indeed a trivial task when accomplished in the digital domain.

Yet optimizing the playback azimuth on an analog master tape is always best done only in the analog domain.

Complex algorithms in DSP plug-ins that purport to restore high frequency loses resulting from azimuth misalignment in the analog domain are only guesses at restoring unknowable information. The initial domain transfer is a step that requires the greatest of care.

As for the importance of inter-channel phase matching to stereo imaging, keep in mind that when a stereo program has equal amplitude versus time in both channels (in other words, has high inter-channel program correlation), the stereo sound field collapses into a mono point source.

Most mastering engineers are using inter-channel phase adjusting tools mainly to avoid undesirable comb filtering. (See Bob Katz's Mastering Audio for a discussion of this.) Other tools are employed for establishing a solid image location.
 
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topoxforddoc

Well-Known Member
Feb 20, 2015
67
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138
Cheltenham, UK
Fred,

Thanks for all this detailed insight. Can I just ask (as a relative beginner in this field - I'm not an audio engineer, but a cancer surgeon) - do you think that my original answers to your questions are reasonable, or do I need to tweak what i do?

Thanks

Charlie
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
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Fred, . . . do I need to tweak what i do?

No, Charlie, I think you're doing fine.

You had a good teacher and you show some understanding of the subject. That puts you well ahead of what many others are doing with tape playback.

By the way, it's always a very good sign when tapes made on different machines will also replay on different machines without a need for playback azimuth adjustment. But unfortunately this is too rarely seen in tape interchange.

My point in this thread was to emphasize that a playback azimuth check and/or adjustment is mandatory when playing back a tape that has been recorded by others. All true analog tape professionals know that the reproducer's play head (just another name for the repro head) must be azimuth aligned to any given tape. (Unless you somehow don't care about the possible loss of higher frequencies in your playback of the recorded program.)

We could now start a new thread about putting meaningful calibration tones on pre-recorded tapes, if there is sufficient reader interest?
 

topoxforddoc

Well-Known Member
Feb 20, 2015
67
6
138
Cheltenham, UK
No, Charlie, I think you're doing fine.

My point in this thread was to emphasize that a playback azimuth check and/or adjustment is mandatory when playing back a tape that has been recorded by others. All true analog tape professionals know that the reproducer's play head (just another name for the repro head) must be azimuth aligned to any given tape. (Unless you somehow don't care about the possible loss of higher frequencies in your playback of the recorded program.)

We could now start a new thread about putting meaningful calibration tones on pre-recorded tapes, if there is sufficient reader interest?

Fred,

Many thanks for that. I'm sure that Stewart will be smiling down on me for taking this in. Your point about line up tones is also valid too. My normal workflow when duplicating or recording is as follows

Tones at head - 30 secs each of 1k, 10k, 100, and 15k tones at zero level PPM4 (with no NR) - followed by record 30 secs Dolby SR set up noise if using my Dolby 363 unit - and then record music.

Does that seem a reasonable way forward?

Charlie
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
I think I understand. Thank you Fred.

Charles

Hi Charles,

A much better (and far more thorough) explanation is found in AES Preprint 1666: “Azimuth and Interchannel Time Displacement Error in Multi-track Tape Recording”

Jay McKnight was the author.
 

c1ferrari

Member Sponsor & WBF Founding Member
May 15, 2010
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Thank you, all, for an erudite discussion. :cool:
 

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