#18 - Sound-in-Syncs Part 2: New revelations, experiments and teardown 

The fact that people with past involvement and expertise pitch in is fantastic. Super interesting, thank Matt.

For those who remember Grandstand on a Saturday on the BBC, most of the sound from the OB truck was carried over SiS in some form, either via direct video link, microwave or Sat. The sound supervisors all had various ways of pre eq-ing the audio going in the SiS encoder to cope with the detrimental effects of the anti-alias filter and the 10 bit compander. There were complaints that the starter's gun in athletics sounded a bit lacking in 'bang' otherwise. Major OBs would have standard analogue 15kHz music lines provided by the Post Office (BT) with video+SiS as a backup, though for convenience at TVC, quite often the analogue audio circuit would be forgotten about, as the SiS sound was easier the manage with the audio being embedded in the same video. Often at major dual media (Radio & TV coverage) events such as horse racing or rugby internationals it was common for the radio broadcasters use a video circuit with SiS as there was more spare capacity in the video provision. Of course, any BBC piece of audio equipment of that era would have B-gauge (PO316) sockets for audio connections to supplement the XLRs. The entire sound desk patch bay (jackfield) and ancillary racks in the OB truck were PO316. When 'Bantam' mini plugs were introduced in the early 1980s to save space, the reliability of the audio connections went down significantly. Would you need a filter on the DAC output if you are feeding the signal into a line output transformer? I'm guessing a coupling capacitor and the inductance of the transformer would do the job. Transformers are probably manufactured by Sowter BTW.

One thing to remember when discussing SIS is that it wasn't limited to use for transmission distribution - BBC Outside Broadcasts (and the EBU) used SIS extensively for outside broadcasts over microwave and satellite circuits - where NICAM 728 compatibility was a non-issue (you would have been going analogue in at the OB end and analogue out at the network centre end - not baseband NICAM or PCM digital) - and having stereo SIS gear to link OBs back to base in stereo was a major requirement (Sony PCM F1s were sometimes used on a second circuit in the very early days I believe, as well as for Radio OBs) The NICAM 3 / 676 stuff may well have been an attempt to solve that problem (ignoring transmission distribution to NICAM 728 TV transmitters) - as you only needed the decoder and encoder at either end to be compatible.

Oooh, now THIS is interesting. I've been fascinated by this for a long time.

Very interesting! Also, HOLY F..K that PCB burn!!

One other thing I've been told in the past - which may or may not be true - is that the RE DSIS system was easier to remodulate to NICAM and needed less re-framing. It could be that the TVT SiS fixed data burst vs the RE slightly variable data burst is related to this ? (It could be that RE's system requires less buffering?)

Its likely the bang was the electrolyte across two high voltage tracks and creating a short, as I've experience this in the past and finding no damaged components.

Those reframer interruptions were heard on NICAM whenever a BBC regional centre switched itself into and out of circuit before a regional opt-out (called soft-opting). AIUI the opt-out switch switched between incoming Network with Dual Channel SiS and local studio with its own Dual Channel SiS. Before the actual switch to the regional output, the local studio would have network vision (and decoded dual channel SIS audio) on its sound and vision mixers, and the output of that studio would be Dual Channel SIS encoded. The opt-out switch - that switched the local studio into the transmission path would switch from incoming network with SiS to local studio with SiS (with the local studio carrying the same incoming sound and vision as network). Then when the opt-out was called the local studio would cut away from network sound and vision to local sources for the duration of the regional opt, at the end you'd cut back to network sound and vision, and then the opt-out switch would be moved to take network (with network SiS) clean - and you'd get another reformer interruption.

B-gauge jacks were standard in BBC analogue audio jackfields and on BBC sound gear - so not surprising they were used on the BBC TVT stuff.

Sorry - bit of a comment stream. Interesting that it's a BBC BASIC running on a Z80, as the BBC Micro was 6502-based (not Z80). However there was a Z80 BBC Basic used for the BBC Micro Z80 Second Processor (and it was also sold for other Z80 platforms). Richard Russell, who worked for the BBC in Designs Dept, developed a lot of in-house equipment, and was heavily involved with the BBC Micro, and keeps BBC BASIC alive across a number of architectures, may be able to advise.

I'm trying to learn ARM assembly, based on BBC Micro but risc. Been looking at the Atari/Amiga/Acorn demo scene. God help us. 😎 🖋