Radio 3: pre-echo on Liszt loud piano parts

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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by James Perrett »

Hugh Robjohns wrote: Sun Jul 25, 2021 7:08 pm Possibly... although that tinkly bell in the back of my head is suggesting pink... :eh: There definitely was a green-backed tape though...

According to

https://www.vintage-radio.net/forum/sho ... hp?t=33281

you are right.

There definitely was a green backed tape because I have some here that I think was ex-BBC which I bought many years ago from an auction.
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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by Tim Gillett »

forumuser840717 wrote: Thu Jul 22, 2021 4:58 pm That's been a problem for years. It's particularly annoying when the stripy leader is used between tracks!

Some tapes and some leader tapes are more prone to it than others and it's really important to check for stripy leaders before baking tapes as that can make adhesion considerably worse (though, in very rare cases, it can also cause it to release).

Similarly, some will release with various solvents ranging from water to different strengths of alcohols or even acetone, while some tapes are destroyed by the solvents so experimentation and note keeping are important.

James, myself and others on this forum are involved in transfer of legacy open reel tapes and are interested in hearing more details re what you say here. Perhaps it needs to be more widely known about in transfer/digitisation circles. Are you aware of which tapes are most vulnerable to this interaction with the stripy leaders?

If baking a SSS tape usually makes the adhesion between the oxide layer and the stripy leader even worse, that seems akin to being caught between a rock and a hard place!
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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by James Perrett »

Tim Gillett wrote: Mon Jul 26, 2021 4:27 am If baking a SSS tape usually makes the adhesion between the oxide layer and the stripy leader even worse, that seems akin to being caught between a rock and a hard place!

Standard practice is to insert a length of plain leader in place of the stripy leader if you are going to bake the tape.
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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by Tim Gillett »

James Perrett wrote: Mon Jul 26, 2021 11:54 am
Tim Gillett wrote: Mon Jul 26, 2021 4:27 am If baking a SSS tape usually makes the adhesion between the oxide layer and the stripy leader even worse, that seems akin to being caught between a rock and a hard place!

Standard practice is to insert a length of plain leader in place of the stripy leader if you are going to bake the tape.

Obviously, but I was thinking of the cases mentioned here where such stripy sections are "used in between tracks". Baking can temporarily prevent the tape from adhering to its adjacent tape winds but unless I have misread forumuser840717, the baking usually makes the oxide layer stick even more firmly to the stripy leader sections throughout the reel. We destroy parts of the tape by baking, or destroy other parts of it by not baking.

I sought more information and guidance about addressing that. I had assumed from what you wrote that you had sought such clarification also.
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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by James Perrett »

I think there's a misunderstanding here. If baking a tape with stripy leader, I will replace the stripy leader between tracks before baking. I wind the tape directly from one reel to the other when doing this so as not to clog up the tape machine. The only disadvantage is that the tape isn't packed so evenly after doing this.

I just tried some IPA on one of the problem leaders - in this case (Scotch 256 and blue striped leader) it didn't seem to make any difference. Fortunately on this tape the engineer had left a gap before the music started so this was more of an academic exercise.
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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by Tim Gillett »

Fair enough. I was thinking of the cases of tapes with such severe hydrolysis that even winding the tape directly spool to spool without first baking risks tearing the oxide from the base layer.

Thankfully I've not experienced such severe cases but have read about them in the literature.

The more common problem I've faced is non sticky/sheddy tapes with multiple splices (perhaps cheap "seconds" tapes made up of multiple short off cuts) where the splice adhesive has oozed onto adjacent tape layers. Just playing the tape normally would have destroyed tape sections at those points. It took me hours to just successfully unwind such a 7" reel without damage, playing the tape at ultra slow speed (slower than 15/16ips) so as to visually catch the first sign of an adhesion before the tape unwound and was torn. I applied and reapplied IPA with a tiny make up brush to soften the adhesive at each point of contact. Very slow work.
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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by Hugh Robjohns »

I've come across an interesting uncredited article about the BBC tape types in the BBC's ENG INF magazine from 1982. I thought it might be of interest so I've edited it slightly to make more sense to modern readers here:

The BBC began the routine use of magnetic tape for audio recording in 1952, following a period of experiment and development. Over the next five years tape almost completely displaced discs as the standard recording medium, with tape stock being manufactured by EMI, Kodak and Kramer (a Canadian Company).

Most BBC 'recording channels' in the 1950s were equipped with EMI BTR2 tape recorders and used EMI’s H50 tape. These early tapes with paper or acetate bases varied in quality and performance due to variations in the size and thickness of oxide granules on the tape. EMI continued to research and develop tape formulations and construction and by 1960 had replaced H50 with H77 on a PVC base with a more consistent performance and around 4dB improvement in signal to noise.

In the 1950s each recording machine was operated by an engineer who set the bias and aligned the recording level for each and every reel of tape, but H77 was sufficiently consistent for standardised settings to be used.

As magnetic tape gained in popularity as a professional recording medium more and more different types were produced. The BBC was recording more programmes than had been practicable in the days of disc recording and so began to search the market for the most suitable tape type available.

In selecting a tape type it was necessary to find an acceptable compromise between signal/noise ratio, print-through, and maximum overload level, and the BBC would not accept an improvement in one or two of these characteristics to the detriment of the other. In particular, given the duration that recordings were routinely stored, there was more concern about print-through than other professional users might have had. A special test was devised, where pulsed tone was laid on the tape which was then stored for 72 hours, after which the level of print through was measured. The figures obtained were often significantly different from those quoted by the manufacturers which were generally based on 24 hours storage!

In 1969 the BBC issued a specification for its first 'standard tape' referred to as Type 100 tape, which was based on EMI 815 with a PVC-base and a coercivitity of approximately 300 Oersteds. Supplies were available from both EMI and Ilford (Zonal). Unfortunately, the PVC base was subject to pinholes which led to dropouts and frequent rejection.

The manufacturers subsequently changed to a polyester base and the BBC revised the specification to Type 101. However, since the operational use of the two tape types was exactly the same and the new type came very soon after the original spec, Type 101 format tapes were commonly referred to as Type 100 by most users.

Type 101 was the mainstay of BBC mono recording work from its introduction until early 1980 when, because of the recession and rationalisations in the recording industry, supplies of unbacked tape ceased. Small quantities of Type 101 tape were being reclaimed for use at some BBC Local Radio Stations through the mid-1980s. In the 1980s the BBC was using around two-hundred thousand 10.5-inch reels of tape per year. (A 10.5-inch NAB reel held 2,400 ft. of ape and ran for 32 minutes at 15ips).

However, by the late 1960s the BBC was experimenting with stereophony and a search began for a suitable tape for stereo work. A higher recording flux-density was needed for two-track work and a physically stronger tape which was less susceptible to edge damage. The introduction of stereo broadcasting was accompanied by the BBC’s bespoke PCM digital distribution system and UK-wide high-quality broadcasting; 15kHz audio bandwidth was needed.

By the start of formal stereo broadcasting in 1972 the BBC had adopted a new tape specification for stereo work: Type 102. This was a backed tape based on 3M's Scotch 262 (with its distinctive green backing), and each track was capable of a peak flux level of 600 nanoWebers per metre (nWb/m). This new tape spec was fully compatible with full-track mono recording machines, producing a peak flux level of 400 nWb/m to a full-track head.

No sooner had Type 102 been adopted than a search began for an even better stereo tape. Although Type 102 matched the capability of typical recorders in use at the time, like the Studer A62, it was clear that the next generation of studio recorders — like the Studer A80 and Telefunken M15A — were capable of recording at a much higher flux level.

Although many new tape types were becoming available, most gave improved performance at the expense of print-through. Professional recording studios mostly operated at 30 ips. and then transferred the recordings to disc, so were not so concerned about print-through.

Eventually Agfa PEM 468 was found to be the best tape format for BBC use, and a specification for BBC Type 200 was drawn up based closely upon it. Type 200 required much more bias flux than most older tape machines were designed to supply, although Studer’s A62s, B62s and some Nagra recorders could be modified to meet its requirements. By 1982 over 40% of the BBC's recording channels had moved onto Type 200, leaving only External Broadcasting, Local Radio and News and Current Affairs departments still using Type 102.

Type 200 used a peak recording flux level of 1012 nWb/m and delivered a 5dB improvement in signal-to-noise ratio, stemming from a 4dB higher recording level and a 1dB improvement in tape noise improvement — the best that could be obtained from the analogue tape machines and tape formulations at that time. Throughout the mid-80s the BBC progressively changed to Type 200 as older recording machines only capable of using Type 102 were replaced.

Any further analogue quality improvements would only be possible by introducing noise reduction techniques which, with over 1000 machines in use across the BBC, would not have been financially viable.

Economics and availability of supplies were expected to precipitate any future changes in tape types, rather than improved recording quality, so in the interests of ensuring continued supplies of Type 200 tape the BBC routinely placed 3-year contracts for tape supply.


... and by the early 90s analogue tape recording was being replaced wholesale by digital recording using DATs, CDRs, and various disk-based systems.
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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by FrankF »

Very interesting that there's no mention of Ampex tapes in all of that.

That said, my abiding memory of Ampex is peppered with swear words and flecked with the spittle of despair, as I transferred all my recordings from a Fostex analogue to an AKAI digital, and shovelled up the fragments from the carpet...
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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by Hugh Robjohns »

I don't recall any Ampex tapes being used at the BBC. I can remember 3M/Scotch, Zonal (Ilford), Agfa, BASF, and EMI tapes...

I doubt the BBC would have selected an American manufacturer due to potential supply issues. I think it only selected European manufacturers.
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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by Tim Gillett »

FrankF wrote: Thu Aug 05, 2021 12:28 pm Very interesting that there's no mention of Ampex tapes in all of that.

That said, my abiding memory of Ampex is peppered with swear words and flecked with the spittle of despair, as I transferred all my recordings from a Fostex analogue to an AKAI digital, and shovelled up the fragments from the carpet...

It's true some Ampex tapes exhibited binder hydrolysis, but so did some 3M Scotch and Sony tapes. Possibly some BASF tapes and others. Countless recordings were affected. The standard temporary fix of controlled baking before winding or playing tapes has been in use for decades.

Unfortunately because it involves raising the temperature of the tape to 50 deg C or more for maybe 24 to 48 hours or more, tape baking will tend to make the print through problem, the subject of this thread, even worse. But it's been found to be a sensible tradeoff compared to possibly ruining the recording by attempting a play without first baking out the moisture.

I once tried to manually remove pre and post echo in a solo voice recording running to some six hours. It involved sampling some room ambience and cutting and pasting the ambience into all silences between the speech. Sometimes the speech wasnt enough to mask all remaining echoes but overall it made for a more listenable product. Maybe someone has developed a software tool which can sense silences prone to print though echoes and automatically substitute in clean room ambience.

https://richardhess.com/notes/formats/m ... ing-tapes/
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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by MOF »

I remember some years ago there was a gentleman from America who wrote for SOS for a while, he had links to a company that used a vacuum process instead of baking. I think a chemical was added that prevented hydrolysis happening again.
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Re: Radio 3: pre-echo on Liszt loud piano parts

Post by Tim Gillett »

Yes I believe vacuuming is also effective but apparently the treatment time frame is much longer.

I guess the problem with any sort of sealant to lock out moisture re entry would be that it would have a thickness resulting in a minute separation of the oxide from intimate contact with the head face, or a "spacing loss", which is notorious for loss of highs in playback, similar to a dirty head.

A similar technique involving "wet play" of tapes which squeal on playback, resulting in nasty FM modulation of the audio, reduces the squeal but also results in a significant loss of highs in the transfer, again due to spacing loss.

So often real world solutions involve trade offs.
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