9. Vertical Interval


The problems with timecode and synchronisation wouldn’t go away. As early as 1984, the engineers at Television Centre (TC) had confirmed that the ‘linear’ audio tracks of a normal VHS machine weren’t sufficiently reliable for conveying timecode. They had proposed the use of Vertical Interval Timecode (VITC), a mechanism whereby timecode was embedded in unused ‘lines’ of information outside the normal area of the television picture. This required a special device known as a ‘VITC reader’ which provided normal SMPTE timecode that could be fed to a standard timecode reader.

Stop Gap

By the summer of 1986, these VITC readers still hadn’t materialised. As an interim solution, it was suggested that timecode could be recorded on a hi-fi ‘track’, as provided on high-quality VHS recorders. Such ‘tracks’ used frequency modulation (FM) to combine stereo audio material with the video information recorded by the machine’s rotating head. The left-hand FM channel could be retained for a mono audio signal whilst the right-hand FM channel would be used for timecode.

At the end of the year, the first Philips VHS machines arrived. These had been modified so that any recording made onto the machine’s mono ‘linear’ track would only be fed from the left-hand input. Unfortunately, it seems that no-one had actually noticed that these machines could only be ‘advanced’ in four-frame increments, making them totally useless for Radiophonic operations.

Early in 1987, three Ferguson 3V53 VCRs replaced the Workshop’s original 3V23 machines. These new recorders, which could be ‘inched’ frame by frame in both directions, were initially provided by Radio Rentals, although by August the Workshop had purchased a total of six machines. Meanwhile, two of the unsuccessful Philips VCRs were connected together to create a video dubbing facility.

The new 3V53 machines didn’t provide a complete answer to the timecode problem. To some extent, the use of hi-fi tracks was a retrograde step. Timecode was now only available when the tape was running at normal speed: when the tape was ‘inched’ forwards or backwards nothing was produced.

VITC Muddle

In 1987, the Workshop received its first VITC readers, although it took another year to get the next pair. And so, having persuaded everyone at TC that the Workshop needed hi-fi VHS tapes, it now had to ask for VITC tapes instead. And the technical problems didn’t go away. For example, VITC disturbed Syncwriter whenever the VCR was in ‘pause’. This was due to the VITC reader producing timecode at one-tenth of normal speed when the tape was stopped. Jonathan Gibbs eventually fixed this problem and persuaded Syncwriter to generate MIDI timecode (MTC) from incoming timecode. Even so, the author never understood why it was necessary to create this superfluous timecode in the first place. After all, a normal tape machine didn’t produce timecode when the tape was stationary!

The BBC VITC readers also had another ‘feature’ known as ‘flywheeling’. This was designed to ‘smooth over’ missing VITC frames but had dreadful side-effects. For example, if a frame of 02:20:21:22 was followed by an erroneous frame of 03:20:21:23 (advanced by one hour) the VITC reader generated all the timecode values for the entire hour. And when the next correct frame of 02:20:21:24 appeared it would ‘flywheel’ the timecode all the way back! In terms of normal timecode, this was similar to spooling a conventional tape against a machine’s heads at high speed. This vast amount of data would have horrific effects on Syncwriter. Eventually, all the Workshop’s BBC VITC readers were fitted with alternative ROMs that fixed the problem. By the autumn of 1988, an Audio Kinetics VITC reader was also being investigated, in the hope that it might be more satisfactory.

There were also problems with the quality of VITC, as well as a lack of understanding at TC concerning the kind of tapes that were required by the Workshop. To work properly, every tape had to contain ‘continuously ascending’ or ‘programme time’ timecode. In other words, the timecode had to progress steadily upwards throughout the entire recording. Unfortunately, some tapes contained the ‘time of day’ of the original recordings. This introduced discontinuities in the timecode, causing Syncwriter to hop around all over the place, depending on the material that had been edited together.

Another complication appeared in the winter of 1988. A VHS tape arrived, but the VITC didn’t work, though TC insisted that it had VITC. Apparently, the tape came from a new type of video editing suite and contained two sets of VITC information. Lines 8 to 10 of the video signal contained normal ‘programme time’ whilst lines 18 to 20 gave the ‘time of day’ of the original recordings. This threw everyone completely, since the VITC ‘test tape’ only had data on lines 18 to 20. Apparently, the BBC VITC reader took data from all the lines, got confused and didn’t display anything. Fortunately, the Audio Kinetics VITC reader allowed selection of VITC lines, although it was more expensive.

In the spring of 1989 another BBC VITC reader arrived, supposedly modified for line selection. It turned out that this only provided timecode via its serial port, the normal longitudinal SMPTE output having been removed to improve the speed of operation! Although attempts were made to connect it to the serial port of a Macintosh computer, this wasn’t considered a sensible option.

U-matic Games

Early in 1989, much to everyone’s horror, the mandarins at TC declared that the VHS tape format wasn’t reliable enough for use with VITC! Initially, the Workshop considered buying equipment that would allow the department to ‘regenerate’ the VITC on VHS tapes via a dubbing process. However, this required a ‘capstan lock’ VHS player, time base corrector (TBC) and VITC inserter (which also provided ‘character insertion’ for making ‘burnt-in’ timecode), all costing a mere £7000!

In August of 1990 a playback-only Sony U-matic video machine was demonstrated. Although it didn’t have ‘frame-advance’ it worked well with VITC. Machines suitable for the Workshop would cost £4,000 each, expensive compared with VHS. In the same month, an Avitel timecode generator and reader was ordered: this could produce and decode both longitudinal SMPTE timecode and VITC data. By the end of the year, all the studios had U-matic machines, although not all composers were keen on this ‘non-standard’ format. Some studios were fitted with a switch that allowed the composer to choose between timecode from the multitrack machine and timecode produced by the VITC reader.

Inevitably, things went wrong. For example, in 1990, Elizabeth Parker received a tape without VITC and with timecode on the wrong audio channel. And Richard Attree got a U-matic tape that had been transferred from a VHS ‘pre-edit’ tape. Sadly, they hadn’t regenerated the VITC, so it was unreliable!

In the autumn of 1991, it was discovered that the U-matic machines ‘muted’ the data on lines 19 to 21 whilst in ‘search’ mode. But then (after originally rejecting Ray Riley’s good advice) the author moved a mysterious TBC (Time Base Corrector) switch at the rear of the machine. This quickly fixed the problem, although VITC data was still lost when searching at very high speed.

Lock to the Future

The later generation of MIDI interfaces accepted longitudinal SMPTE timecode, although they didn’t always like working with some types of VITC reader. For example, the Opcode Studio 3 interface automatically advanced timecode beyond any interruptions, but this made the timecode ‘dither’ whenever the VCR was in ‘pause’ or ‘stop-frame’ mode. This problem could be minimised by using the Avitel unit as a VITC reader, which always generated timecode at the standard rate. A BBC VITC reader, on the other hand, only produced timecode at one-tenth speed during ‘pause’ or ‘stop-frame’.

Sadly, the Avitel unit’s latter feature also made it ‘crash’ the computer in Studio B, partly because HyperCard couldn’t cope with the data arriving at the computer’s serial port. Hence the Avitel unit was replaced by a standard BBC VITC reader. In addition, the composer was advised to disable timecode when not in use (by pressing a button on the Studio 3) and to avoid using HyperCard.

There were various ways of sending timecode through a MIDI interface and computer, depending on the sequencing software and the interface itself. For example, Vision accepted standard MIDI Timecode (MTC) messages whilst Mark of the Unicorn’s Performer preferred proprietary MIDI codes known as Direct Time Lock (DTL) or Direct Time Lock enhanced (DTLe), although it could also use MTC. Unfortunately, DTL behaved strangely with VITC, although this wasn’t actually a fault. Whenever a video tape was stopped the timecode on the Mac still counted upwards, simply because the VITC reader continued to generate timecode, intimating that that the tape was actually moving!

Early in 1991, a new MIDI interface known as the Video Time Piece (VTP) was produced by Mark of the Unicorn. This could read VITC directly and convert it to ‘burnt-in’ video, longitudinal SMPTE timecode, MIDI Timecode (MTC) or almost anything else. In addition, it could generate its own SMPTE timecode. Although perfect for American NTSC tapes, it didn’t work as well as the Avitel reader on European PAL tapes and was sensitive to the level of VITC signal. Furthermore, the VTP provided SMPTE timecode at 0 dB, too low for feeding any quarter-inch tape machine that used centre-track timecode. The Workshop’s VTP was therefore modified to give an output of +3 dB. And, even with a new ROM, the VTP didn’t retain its default settings on power-down.

A VTP was originally installed in Studio C, but this refused to work with the StudioVision sequencing application, although it operated normally with Performer. In desperation, the author connected the regenerated timecode output of the VTP to the timecode input of the Opcode Studio 3 interface and it worked. The problem was caused by differences in the way the two applications worked. Whilst Performer asked the VTP to provide ‘full timecode’ MIDI messages, StudioVision relied on an automatic feed of such messages, as provided by the later Opcode Studio 5 interface.

In 1992, Studio C suffered from the usual problem of the Avitel reader generating timecode whilst at rest. The composer was advised to move the ‘VITC’ switch on the Avitel to ‘off’ when not in use.

In the autumn of 1992, the outputs of the BBC VITC readers were increased by 6 dB, making them suitable for driving unbalanced destinations. They were also fitted with standard jack sockets on their outputs and IEC mains connectors.

Wisdom of Hindsight

Looking back, it can be seen that VITC was a waste of time and money. Instead of facing commercial reality, the Workshop was led along a road of engineering idealism that was far from ideal. The author, instead of investigating the matter for himself, took half-informed advice from others. And yes, today’s composers often use hi-fi VHS cassettes, usually with timecode on one audio track!


©Ray White 2001.