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