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Adding a 3rd Tape Head to (mono) Reel-to-Reel.

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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Hugh Robjohns » Mon Sep 02, 2019 10:04 am

It's an interesting point because it allows tapes recorded in the late 40s and 50s to sound remarkably modern.

Back in the 50s replay head-gaps were relatively wide, and thus the HF response of tape machines back in the day was fairly curtailed. But the electronics in the tape machine usually had a wide-bandwidth and, since the record head-gap doesn't really affect the recorded frequency response, the actual recorded signal stuck on the tape really was a wide-bandwidth signal. That HF just couldn't be heard on replay at the time... But replayed today on modern narrow-gap machines, and all that original brilliance comes back the way the recording engineers heard it directly from the mixing console feeding the tape machines at the time.

An excellent example is Quincy Jones' Birth Of a Band albums from the late 50s, now transferred to CD. Remarkably modern-sounding records with plenty of top end that never made it onto the contemporary vinyl pressings -- and that top end isn't from mastering EQ, it's just because that HF really was recorded at the time, but it needed modern tape machines to replay it! :D
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Hugh Robjohns » Mon Sep 02, 2019 10:06 am

Folderol wrote:Dear me. Talk about bringing back memories! :bouncy:

There's lots of lovely tangible science involved in tape recording... and lots of physical and technical imperfections and limitations in the medium that were circumvented in so many ingenious ways.

If you were starting today no one would consider magnetic tape -- or vinyl for that matter -- sensible ways to capture, store, and reproduce audio... :lol:
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Martin Walker » Mon Sep 02, 2019 10:08 am

Hugh Robjohns wrote:A classic example is Quincy Jones' Birth Of a Band albums from the late 50s, now transferred to CD. Remarkably modern-sounding records with plenty of top end that never made it onto the contemporary vinyl pressings -- and that top end isn't from mastering EQ, it's just because that HF really was recorded at the time, but it needed modern tape machines to replay it! :D

Wow, fascinating stuff Hugh - it's not often that we can retrieve data from the past with greater fidelity than at the time :shock:


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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Tim Gillett » Mon Sep 02, 2019 11:47 am

Hugh Robjohns wrote:It's an interesting point because it allows tapes recorded in the late 40s and 50s to sound remarkably modern.

Back in the 50s replay head-gaps were relatively wide, and thus the HF response of tape machines back in the day was fairly curtailed...

That's interesting. I seem to recall that in the late 40's/ early 50's Ampex were mainly concerned to satisfy the FCC broadcast stipulation of an upper 15 kHz limit, as they were working hard to have their new professional tape machines accepted in the broadcast industry. At first Ampex achieved 15 kHz response at 30ips. Soon afterwards they were able to maintain the same 15 kHz response but at 15ips, halved tape speed. This was the late 1940's when tape stocks were inferior to what they would become in the mid to late 50's.

So I'm not sure that even around 1950 they couldn't make a repro head with narrower gap, so much as they didn't see the need to do so, to go above 15 kHz as the upper frequency limit for playback. A 20 kHz upper limit seems to have been a more modern standard or expectation.

You mentioned the full upper range not making it onto the vinyl records of the day. Part of that may have been a deliberate choice to LPF so as not to allow those troublesome highs to be cut onto the disc master. Especially problematic in the inner grooves.

I have in my LP collection a disc named Aretha's Gold. From day one it didn't sound right, and with every play it sounded harsher. A few years ago I decided to look at the audio on the spectrum analyser. It showed a low level but very visible 17 kHz sine wave right through both sides. (It was beyond my hearing range even in my 30's.) Enough to make especially the inner tracks very distorted. Then there were the ill fated 4 channel vinyl experiments of the 1970's where they cut a 30 kHz tone with rear speaker information. So perhaps it was just as well if such upper frequencies on tape masters never made it to vinyl...

But transferring to CD or even higher res formats? A different story perhaps.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Hugh Robjohns » Mon Sep 02, 2019 11:57 am

Tim Gillett wrote:So I'm not sure that even around 1950 they couldn't make a repro head with narrower gap, so much as they didn't see the need to do so, to go above 15 kHz as the upper frequency limit for playback.

You may be right; I can see the logic in what you're saying. Unfortunately, all the people I knew who were working in the industry back in the 50s and 60s are all dead now, so I can't quiz them about these things anymore. :frown: However, the sleeve notes on those albums I mentioned make a big thing about the high-end not being heard before off tape or vinyl...

H
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Tim Gillett » Mon Sep 02, 2019 12:42 pm

Hugh Robjohns wrote:
Tim Gillett wrote:So I'm not sure that even around 1950 they couldn't make a repro head with narrower gap, so much as they didn't see the need to do so, to go above 15 kHz as the upper frequency limit for playback.

You may be right; I can see the logic in what you're saying. Unfortunately, all the people I knew who were working in the industry back in the 50s and 60s are all dead now, so I can't quiz them about these things anymore. :frown: However, the sleeve notes on those albums I mentioned make a big thing about the high-end not being heard before off tape or vinyl...

H

Is that a total surprise?
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Folderol » Mon Sep 02, 2019 12:50 pm

This is almost annoying! I've got a faint memory about something on using a separate head for the bias, opposite the record head, rather than mixing it in the signal.
Ha! Got it :bouncy:
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby James Perrett » Mon Sep 02, 2019 1:55 pm

Martin Walker wrote:Wow, fascinating stuff Hugh - it's not often that we can retrieve data from the past with greater fidelity than at the time :shock:

There are still people working on ways of improving quality from old tapes. I'm currently testing some Dolby A decoding software that claims to retrieve significantly more detail than the old Dolby hardware. There are a huge number of masters that could possibly be improved by using this software.

And of course we have Jamie Howarth's Plangent Process which claims to eliminate wow and flutter using the bias signal or other continuous tones recorded on the tape as a reference.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Hugh Robjohns » Mon Sep 02, 2019 2:31 pm

Yes... I wonder what they'll come up with in the 2060s to improve the reproduction from early digital recordings... :lol:
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Elephone » Mon Sep 02, 2019 5:53 pm

Hugh Robjohns wrote:Yes... I wonder what they'll come up with in the 2060s to improve the reproduction from early digital recordings... :lol:

...or really early wax recordings! Could AI actually re-imagine them into pristine renditions?
That's another story.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Elephone » Mon Sep 02, 2019 5:57 pm

"Martin Walker" Wow, fascinating stuff Hugh - it's not often that we can retrieve data from the past with greater fidelity than at the time :shock:

Martin

Have you heard what they did with the Robert Johnson recordings? They may have made even further enhancements since then.
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Hugh Robjohns » Mon Sep 02, 2019 6:07 pm

I did... and I have some. :-)
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Re: Adding a 3rd Tape Head to (mono) Reel-to-Reel.

Postby Tim Gillett » Tue Sep 03, 2019 6:57 am

Quoting myself here:

Tim Gillett wrote:So I'm not sure that even around 1950 they couldn't make a repro head with narrower gap, so much as they didn't see the need to do so, to go above 15 kHz as the upper frequency limit for playback...

I did a few few quick calculations and cross checked another's figures. https://electronics.stackexchange.com/q ... -tape-head
It seems for a tape repro head to reproduce 20 kHz at cassette speed (1.875ips), its gap length must be 1.2 microns or less. But at 15ips, 8 times faster tape speed, that gap length only needs to be 9.5 microns or less.

In the early to mid 60's, Akai was making tape heads for open reel domestic recording with 1 micron gap lengths. I still have an Akai X-IV portable (Germanium transistors!) which claimed 13 kHz upper freq response at 1.875 ips (cassette tape speed). In the late 1950's, or even earlier, that they couldn't construct a repro head with a gap length of 0.374 thou (9.5 microns),
8 times less critical than what Akai achieved in gap lengths the early to mid 60's seems unlikely.

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