How many people check the repro azimuth on a tape before they play it?

topoxforddoc

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Feb 20, 2015
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Cheltenham, UK
I'm sure that all of the tapeheads on WBF know the importance of repro head azimuth. I was taught this by my good friend Stewart Emmings, who sadly went prematurely to a studio in the sky 2 years ago at the age of 49.

Misalignment of the repro head azimuth leads to loss of high frequency playback, which is much greater on lower speeds and wide tape format, such as reel to reel, and less obvious on 1/8 inch cassette tape. The amount of HF loss is related to track width and tape speed. Hence the HF performance of 15 IPS 1/4 inch 2 track HF replay performance is much more reliant on getting the repro head azimuth correct (see section 3-7 of Morrison's seminal paper in AES) - small errors lead to BIG losses in HF response.

http://aes-media.org/historical/pdf/morrison_stl-manual.pdf

I have about 100 1/4 inch 2 track tapes - some original production masters (2nd gen from stereo mix down) and many dubs from production masters (3/4th gen) - all of these have line up tones at the head, so that I can check repro head azimuth and adjust the frequency response on my repro machine to maximise the sound quality. I do this EVERY time for a new tape coming into my home, which is then copied onto new tape stock as a zero level dub at 15 IPS with Dolby SR (I play the copy and keep the original safe). That's why a studio tape usually has a 15k tone first, so that the engineer can ensure that the tape is played exactly in the manner in which the mastering studio intended.

Repro head azimuth is the same as phono cartridge alignment on a turntable - but imagine that each LP mastering lab might cut the LPs in a slightly different way, so that you would have to align the cartridge on each record to get the maximum out of the groove. Vinyl fanatics (yes I am one of those too) are happy to make sure that cartridge alignment is spot on. Presumably tape heads are the same, or maybe I'm wrong.

Charlie
 
Last edited:

topoxforddoc

Well-Known Member
Feb 20, 2015
67
6
138
Cheltenham, UK
By the way, I forgot to add that some vinyl addicts will have a micrometer adjuster on the tonearm to change VTA depending on whether the pressing is 140, 180 or 200 g - that actually only has a modest effect one SQ - yet a small azimuth misalignment on 15IPS 1/4 inch tape has a very big effect on SQ.
 

topoxforddoc

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Feb 20, 2015
67
6
138
Cheltenham, UK
Hah,now there is the old provenance thing. Were those tones put on the recording machine when the "safety master" was made or were they merely copied from the safety master the safety master was made from. No use aligning the replay machine to tones of one or more generation before the previous dub . If one knows that is good but does one really know?

Absolutely. But the studio tape labels all have boxes on them to show which tones are included with a standard order. They all appear in order at the head when I play the tape. Here's an example.

 

microstrip

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I'm sure that all of the tapeheads on WBF know the importance of repro head azimuth. I was taught this by my good friend Stewart Emmings, who sadly went prematurely to a studio in the sky 2 years ago at the age of 49.

Misalignment of the repro head azimuth leads to loss of high frequency playback, which is much greater on lower speeds and wide tape format, such as reel to reel, and less obvious on 1/8 inch cassette tape. The amount of HF loss is related to track width and tape speed. Hence the HF performance of 15 IPS 1/4 inch 2 track HF replay performance is much more reliant on getting the repro head azimuth correct (see section 3-7 of Morrison's seminal paper in AES) - small errors lead to BIG losses in HF response.

http://aes-media.org/historical/pdf/morrison_stl-manual.pdf

I have about 100 1/4 inch 2 track tapes - some original production masters (2nd gen from stereo mix down) and many dubs from production masters (3/4th gen) - all of these have line up tones at the head, so that I can check repro head azimuth and adjust the frequency response on my repro machine to maximise the sound quality. I do this EVERY time for a new tape coming into my home, which is then copied onto new tape stock as a zero level dub at 15 IPS with Dolby SR (I play the copy and keep the original safe). That's why a studio tape usually has a 15k tone first, so that the engineer can ensure that the tape is played exactly in the manner in which the mastering studio intended.

Repro head azimuth is the same as phono cartridge alignment on a turntable - but imagine that each LP mastering lab might cut the LPs in a slightly different way, so that you would have to align the cartridge on each record to get the maximum out of the groove. Vinyl fanatics (yes I am one of those too) are happy to make sure that cartridge alignment is spot on. Presumably tape heads are the same, or maybe I'm wrong.

Charlie

Great article, the most important picture for audiophiles is shown in page 21 - dB LOSS VS . MINUTES AZIMUTH ERROR AT 15kHz FOR SEVERAL COMMON RECORDING FORMATS - I doubt people will be interested in the Mil Wave length or 1/2 Mil Wave length tables .

However we miss the relevant information to give the due value to this article - what is the typical distribution of azimuth errors in pre-recorded existing tapes? Are we addressing a real problem of most tapes or just the case of a few tapes?
 

topoxforddoc

Well-Known Member
Feb 20, 2015
67
6
138
Cheltenham, UK
Great article, the most important picture for audiophiles is shown in page 21 - dB LOSS VS . MINUTES AZIMUTH ERROR AT 15kHz FOR SEVERAL COMMON RECORDING FORMATS - I doubt people will be interested in the Mil Wave length or 1/2 Mil Wave length tables .

However we miss the relevant information to give the due value to this article - what is the typical distribution of azimuth errors in pre-recorded existing tapes? Are we addressing a real problem of most tapes or just the case of a few tapes?

Thank you. The problem is that you can't tell without line up tones. A muffled recording might in fact be fine, if you could alter the repro head azimuth to align with the record head azimuth on the machine which made the tape. At 15 IPS, 2 track 1/4 inch tape is really susceptible to very small errors, which diminishes the perceived sound quality significantly.
 

microstrip

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Thank you. The problem is that you can't tell without line up tones. A muffled recording might in fact be fine, if you could alter the repro head azimuth to align with the record head azimuth on the machine which made the tape. At 15 IPS, 2 track 1/4 inch tape is really susceptible to very small errors, which diminishes the perceived sound quality significantly.

I have read that azimuth can be successfully optimized using DSP tools checking for correlation between limited bands of frequencies in tracks - unfortunately now we have the tools, but no people are available or interested enough to pursuit this line of research.
 

topoxforddoc

Well-Known Member
Feb 20, 2015
67
6
138
Cheltenham, UK
I have read that azimuth can be successfully optimized using DSP tools checking for correlation between limited bands of frequencies in tracks - unfortunately now we have the tools, but no people are available or interested enough to pursuit this line of research.

I think you can also do this with a spectrum analyser. Correct azimuth is found when the high freq tone signal is peaked. When azimuth is mal adjusted, the high freqs on a spectrum analyser for music shows loss of HF. When the azimuth is correct, the spectrum analyser shows that the freq response is improved with restoration of the HF part of the music.

It does seem strange that no-one is interested to pursue this research and azimuth optimisation, when we have a mini R2R tape revival with new machines and plenty of new software.
 

adrianywu

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Nov 15, 2021
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I think you can also do this with a spectrum analyser. Correct azimuth is found when the high freq tone signal is peaked. When azimuth is mal adjusted, the high freqs on a spectrum analyser for music shows loss of HF. When the azimuth is correct, the spectrum analyser shows that the freq response is improved with restoration of the HF part of the music.

It does seem strange that no-one is interested to pursue this research and azimuth optimisation, when we have a mini R2R tape revival with new machines and plenty of new software.
You can do this with free software such as Audacity. A segment of the digitized signal (up to about 50s) can be analyzed. I have been doing this to compare some of the modern LP reissues with the original production master tapes or LPs to find out what the mastering engineers have done to butcher (sometimes) the sound. The problem is, one cannot do it in real time. That means you have to record the segment, adjust the azimuth in one direction and record again, digitize the segments, compare, and then repeat.
 

Foxbat

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How many ways can you say "Life is too short"?

I also don't check my car's compression and timing every morning.
 
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adrianywu

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How many ways can you say "Life is too short"?

I also don't check my car's compression and timing every morning.
Like people who change the VTA with every LP. Tell them that they change the overhang whenever they change the VTA, and this will give them a nervous breakdown.
 
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Pacha

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I've had R2R in my system since the late 50s. I certainly enjoy my tapes but own no masters or safety copies. I do own a very complete, missing only a small number, of RCA 2 track tapes from the 50s and early 60s. None of these have tones at the beginning of the tape and I only have a Revox PR99 and B77 for machines. I'm sure this adjustment is important when restoring and aligning the deck, I do this on mine, but, neither of my decks make this easy to consider for each play. Even thought, I still find much enjoyment from listening to these tapes.
 

adrianywu

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Nov 15, 2021
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I've had R2R in my system since the late 50s. I certainly enjoy my tapes but own no masters or safety copies. I do own a very complete, missing only a small number, of RCA 2 track tapes from the 50s and early 60s. None of these have tones at the beginning of the tape and I only have a Revox PR99 and B77 for machines. I'm sure this adjustment is important when restoring and aligning the deck, I do this on mine, but, neither of my decks make this easy to consider for each play. Even thought, I still find much enjoyment from listening to these tapes.
RCA 2-track tapes from that era are of very high quality, and I would expect the machines used for copying to be properly aligned. I think you will gain very little by trying to adjust your playback head with each tape. Just align the head with a reference tape and be done with it. The only time adjusting the head for a tape would make sense is when you need to copy the tape and want to optimize the process.
 
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