On the 2nd of April, eleven Members and colleagues gathered at Pinewood Studios for a brief but enlightening presentation by Andy Day of his company's equipment for transmission of high-quality audio between any two locations via ISDN lines. This would normally be done in real time, or masters can be sent in extended time. Typical uses might be to approve mixes, linking studios for ADR or music recording, and sending music or FX.
Normal ISDN lines come in pairs capable of 128 Kbits per second of information, but the Dolby Fax system requires 2 such pairs to give 256Kbits. The terminals use normal copper wiring but of course the connections proceed from the nearest exchange by fibre optic cable. These are configured to provide one or two audio channels with a bandwidth of 20Hz-20kHz at less than 0.2% distortion and a dynamic range of 108dB, plus timecode and machine control if desired for, perhaps, an ADR session where the actor is in LA watching a video picture shuttling under the control of the director and mixer in London. Paradoxically, because the US West Coast area were the first to use ISDN locally they set a standard of only 2x56Kbits/sec, so a 3rd ISDN line is currently needed to communicate from there to elsewhere, but they are gradually changing to the newer World standard of 2x64Kbits.
A Dolby Fax send/receive installation consists of 3 rackmounted units: a digital encoder, a decoder, and an ISDN terminal adapter/multiplexer, plus your (or their) PC. The latter can be used for controlling functions in a session, and even for 'dialling' other listed users from the on-screen list although a palm-top controller is offered as an alternative.
The audio inputs are first converted to 16-bit PCM by the DP523 Encoder and AC-2 coding then reduces the bit rate to a single stream of 256Kbits/sec including any auxiliary data. This is
done selectively on the basis of splitting the audio spectrum into bands which are quantised at a higher number of bits for the higher frequencies than the lower ones. The overall effect reduces the data from 1,400,000 bits/sec to only 256,000 bits/sec thus lowering the call costs considerably. This interfaces via the Dolby "Ascend VSX Unit" to the public ISDN network, and on arrival at the other end undergoes a mirror transformation via a VSX and DP524 Decoder back to analogue or digital outputs. Audio and data can travel in both directions simultaneously. Amongst the optional add-ons are devices to allow transfer of Apple Mac files, such as those from artwork or Avid. The obligatory one for film post-production is our Member Colin Broad's time-code synchroniser, allowing Sony 9-pin machine control to be transmitted alongside the audio. If bit-for-bit transmission is required for master transfers, it takes considerably longer than real time, but provision for it exists when needed.
Andy ended his presentation (from a laptop beamed through an overhead projector - very slick) by adjourning to Pinewood's digital Theatre 3, where he dialled up his Wootton Bassett HQ so we could hear a good quality CD of music thoughtfully left playing by his absent office cleaner. (Giving us an ADR demonstration would doubtless have been a trifle expensive.)
Costs? The purchase of a Dolby system is 6,500. Installation of ISDN lines is cheaper almost anywhere in the world (eg. Germany 80) than here where BT currently charge 800 per pair plus 168 rental per month. However the quality does beat the two cocoa tins joined by string with which I currently give my wife the day's instructions.
Dolby Labs have come a long, international way since starting in London in 1965, and they certainly haven't lost their grip. Many thanks to Andy for the presentation, and to Pinewood for the facilities.