For those who need the authority of a best practices document to justify to higher-ups the time needed to perform azimuth adjustments for each tape, IASA-TC04 has this to say:
5.4.12 Corrections for Errors Caused by Misaligned Recording Equipment
184.108.40.206 Misalignment of recording equipment leads to recording imperfections, which can take manifold form. While many of them are not, or hardly correctable, some of these faults can objectively be detected and compensated for. It is imperative to take compensation measures in the replay process of the original documents incurred, as no such correction will be possible once the signal has been transferred to another carrier.
220.127.116.11 Azimuth and Tape Path Alignment: Inaccurate alignment of the record head of the original recording machine means that at replay, the signal retrieved will exhibit a reduced high frequency response, and, in the case of two or more track replay, an altered phase relationship between the two channels. Adjustment of the angle of the replay head such that the relationship of the head is in the same plane as the magnetised field on the tape is termed the azimuth adjustment and this simple adjustment can markedly improve the quality and intelligibility of the retrieved signal. There is no difficulty in training staff in this task, and good binaural hearing is all the measuring technology required. An accurate phase meter or oscilloscope will aid in the adjustment of mono and properly recorded tapes, they may, however, be misleading on tapes recorded on cheap, domestic equipment. In such cases aural judgement of the high frequencies should be relied on. Additionally or alternatively, a software programme providing a real time-spectrogram function can be used. Azimuth adjustment should be a routine part of all magnetic tape transfers.
18.104.22.168 Digital systems may correct the phase relationship of the signal (often described as azimuth correction), however, such procedures cannot retrieve the high frequency information that is lost. Azimuth adjustments must be made on the original tape before transfer commences.
Director of Technical Operations
Media Digitization and Preservation Initiative
From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of Tom Fine
Sent: Wednesday, September 10, 2014 7:51 AM
To: [log in to unmask]
Subject: Re: [ARSCLIST] recording "cleanup" plugins and 192/24
It's interestng you bring up this topic. I was just reading the book that comes with the new Beatles In Mono LP box and they talk specifically about azimuth on the full-track tapes. Despite the fact that these mono masters were made in-house at Abbey Road, most of them on the same machines, the mastering engineer said he had to adjust azimuth on the fly as records were being cut, especially with the later albums where mono mixes were done days or months apart. His point was, azimuth was specific to each track on some albums. He had made notes and used a gauge-based azimuth adjustment on his Studer A80 playback deck, so he was able to make precise tweaks as the tape rolled between cuts, according to the book text.
I was taught, with full-track azimuth, that you really have to adjust to ear, how the top end sounds best. Keep in mind that time-damaged tapes and poorly slit tapes will likely "country lane" through the transport and wreak havoc with azimuth. Adjusting tones at the head of the full-track tape (when they exist) is somewhat helpful, but ears need to be the final judge.
Azimuth is a tricky thing and I'm still learning about it after 40 years of playing tapes. What I have learned is that it's really critical to solve the azimuth puzzle in the analog domain because problems can't be satisfactorily fixed in the digital domain.
For old full-track tapes, I am curious about using the center two tracks of a 4-track quarter-inch machine. I haven't done much with this, but when there are tones on the tape, you can get a scientific azimuth adjust with a scope. Many old tapes are edge-damaged and I wonder if it's better not to play the outer edges of the tape. However, the effects of country-laning may be even worse if you're grabbing two narrow bands of signal and either combining them or not.
If you want to hear a prime example of azimuth issues, get a copy of the "Sun Records Greatest Hits"
LP that was sold on Record Store Day this year. The tapes were clearly and audibly played back with a 2-track head and either were in such poor shape that they couldn't go through the transport correctly or the playback engineer was inept. In any case, with many of the songs, if you combine them to mono, they flange, "phase effect" and go in and out of treble cancellation, telltale signs of being played out of azimuth. If you listen on a stereo cartridge and don't combine to mono, it's not as bad, it just sounds like bad edge-warp. I think it was inept playback all around, but I've never handled the tapes. I do bet that they'd sound better if played back either through a narrow-width single head capturing the middle 1/2 of the tape height or with the middle two tracks of a 4-track quarter-inch head with azimuth constantly monitored on a scope and tuned to ear.
By the way, even with the less than ideal playback and remastering, the tunes on that Sun LP jump right out the speakers, still hot and rockin' to this day.
-- Tom Fine
----- Original Message -----
From: "Andrew Dapuzzo" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, September 10, 2014 7:34 AM
Subject: Re: [ARSCLIST] recording "cleanup" plugins and 192/24
> While I understand the importance of capturing output "above 20kHz" with
> the aforementioned tools, are there any tools available to help with
> azimuth adjustments? Older recordings, especially those made in the field
> with machines that have been "banged up", may be recorded with azimuth that
> is slightly off. Therefore, the higher frequencies may be lost or
> diminished if playback is not adjusted to the exact azimuth of the original
> recording. Is the only tool available our ears listening as we manually
> adjust the azimuth?
> On Fri, Aug 29, 2014 at 6:18 PM, John K. Chester <[log in to unmask]> wrote:
>> At 04:49 PM 8/29/2014, Tom Fine wrote:
>>> John, is there a modification for to remove those noises? Do 3rd party
>>> electronics also carry those noises or are they something with the power
>>> rails under the transport? Sorry if these are ignorant questions, I'm not
>>> that familiar with the innards of ATR's.
>> I suspect this is neither the list nor the proper subject heading for
>> discussing such a highly technical issue, but here's a brief answer:
>> I have never tried to clean up an ATR with stock electronics, although I
>> have a good idea of where to start. I have no data on 3rd party
>> electronics other than Plangent's. When I got the Plangent electronics to
>> be clean enough for our purposes, I stopped worrying about the problem.
>> Plangent does use a preamp in the headblock with a cable running directly
>> to our box, which helps keep things clean.
>> I do find it a bit odd that folks doing 192k transfers often don't seem to
>> worry about how much signal gets from the tape to the tape machine output
>> above 20 kHz, and how much noise in that region comes from the machine
>> rather than the tape. There are useful signals up there, and we know that
>> if the transfer captures them they can later be used to improve the quality
>> of the audio below 20 kHz that we can actually hear.
>> -- John Chester
>> ----- Original Message ----- From: "John K. Chester" <[log in to unmask]>
>>> To: <[log in to unmask]>
>>> Sent: Friday, August 29, 2014 4:33 PM
>>> Subject: Re: [ARSCLIST] recording "cleanup" plugins and 192/24
>>> At 05:06 PM 8/29/2014, Shai Drori wrote:
>>>>> So if I turn the display off the 28.8 kHz goes away?
>>>> No, that noise on an ATR is actually coming from the reel motor
>>>> drivers. The display generates other noise which starts somewhere in the
>>>> mid-50's of kHz and has lots of harmonics.
>>>> Turning off the display removes a lot of the noise spikes in the audio
>>>> output but not all of them.
>>>> -- John Chester