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Ambisonic Broadcasting


The curiosities of broadcasting, professional video transmitters and the like, are not exactly our line. But the presentation of a few papers at the recent International Broadcasting Convention at Wembley drew us along to see what was happening. Studio Sound are running a report of some sort on the exhibition itself, but the session that interested us was on stereo and 'quadraphonic' (humph!) systems.

The morning consisted of four papers; the first, by D P Robinson of Dolby Laboratories, detailed a system for the use of Dolby-B noise reduction for FM broadcasting, and discussed the results of some continuing tests in the US. Very interesting and useful. The proposed system includes automatic Dolby switching, and should nicely improve s/n ratios and transmitter service areas. Let's hope it comes to the UK. The other three papers were concerned with Ambisonic broadcasting, and we therefore found them particularly interesting. The first of the set was on systems design for Ambisonic broadcasting, and was given by Peter Fellgett of Reading University, one of the inventors of the British NRDC-backed UHJ 'family' of surround-sound systems. He emphasised, cogently, the major differences between UHJ and the other so-called 'quadraphonic' systems: that the aim is to produce a total sound-field around the listener. Thus the system is based on the successful encoding of directions from which sound should come, and has nothing whatsoever to do with four channels, four loudspeakers or anything like that. So we don't talk about 'left front', 'right rear' or whatever. After all, does a concert hall have four channels?

This was followed by a discussion of the IBA's experimental 2½-channel system, given by Dr. J Halliday of the IBA. This neatly coincided with the IBA's announcement of test transmissions by Capital Radio in November/December using this system. Regrettably, information on the correct type of decoder required is not yet available, so we wonder exactly who will be able to listen (why on earth is this the case?). The UHJ family of systems allows a number of channels to be used for surround-sound transmission: either two (as in the BBC's Matrix HJ), 2½, three, 3½, four or more. The use of 3½ or four channels enables height information to be encoded as well as the horizontal, so a total three-dimensional sound-field can be created. 2½-channel encoding theoretically allows better image definition than two channel systems; but the whole family is compatible, so you can get good results with whatever system you can decode, including mono or stereo. So, for example, you'd get good results with the IBA tests even if you only had a BBC-type Matrix HJ decoder unit. The IBA system is referred to as '2½-channel' because it uses a third, bandwith-limited channel, transmitted by quadrature modulation (a form of FM) applied to the stereo difference-signal subcarrier (sorry about the jargon). Most of Dr Halliday's lecture was devoted to demonstrating that the 2½-channel system introduced no more than a 1-3dB increase in noise level as compared with a normal stereo broadcast (which is 20dB noisier than mono!). Interesting.

The final paper was presented by the BBC's Chief Engineer (radio broadcasting), J Duncan MacEwan, and was intended to be a review of the first year of experimental Matrix HJ transmissions, which have included 11 rock items, 51 orchestral concerts, and a fair amount of drama and experimental material. Although dogged by union problems, the results have been very significant. But somehow the lecture seemed a bit 'off'. Matrix HJ is a good ambisonic system, cheap decoders are available (primarily from Integrex) and it's not really inferior to the IBA's system (they're both part of the UHJ family, the IBA's 2½-channel form offering slightly superior position definition to the BBC's 2-channel version, at least in theory). Yet the BBC's approach seems to be dogged by obsolete 'quadraphonic' terminology: diagrams of square sound-fields, front-to-back and left-to-right panning instead of proper Ambisonic panpots able to place a sound anywhere in the sound-field, annoying references to 'left-front', and the like (the speakers should not be apparent as sound sources — it's a sound-field, not a four-source system). The BBC has made good use of developments like the Calrec Soundfield mic, but advances like these were lost in the antique terminology. A great pity, because the BBC's results are far, far better than MacEwan made them sound; surprisingly good, in fact, bearing in mind the BBC's undercapitalisation and the fact that they're forced to use equipment that should be in the Science Museum because they can't afford better.

Meanwhile the IBA's UHJ mobile (see SI August News) will be in use for the forthcoming 2½-channel tests. We'd like to see the Beeb with one, too; they'd make good use of it, we're sure. But at least a hint of good things to come is in the IBA's press release: 'These tests are in support of studies being made by the European Broadcasting Union...' — maybe we'll see the UHJ family adopted as the European surround-sound broadcasting standard, and then perhaps we'll see UHJ-encoded albums too... let's hope the FCC takes the hint. Richard Elen

AKG Bonanza



AKG Acoustics seem to be pushing out a new goodie every month, and because their gear's really interesting, they get another mention (that's the only criteria for news pages, folks: interestingness).

This month we're taking a look at AKG's new stereo mics, the C422 and the C34. The 422 is a biggie; basically two C24s stuck together, the top section can be rotated through up to 180° and the bottom through 0° or 45° with reference to the housing, thus enabling fine 'aiming' even when the mic is stuffed on a stand, and easy switching from MS to XY stereo formats. And another goodie feature: a LED on the front tells you what the mic is 'looking at' - ideal for dim rock studios and drooping mic-stands.

The smaller C34 is based on the CK1 capsules, used in the marvellous C451 (which must be, with the Neumann U87, one of the best-known studio mics), one pair of capsules is fixed, while the other half moves through up to 180°. You may turn your heads in dismay when I say one pair of capsules, but this is not just a cardioid mic: each section uses a pair of capsules, giving up to nine possible polar diagrams by merely varying the voltage on one of the capsules in the pair. This adjustment is noiseless, so you can do it in midtake, if you're that way inclined.

Both C34 and 422 are operated from the same control unit-cum-power supply, the S42E.

Also new are two mic heads, the CK4 and the CK22. The CK4 is a high-quality (of course) bi-directional capsule for interview work where side-signal attenuation is very important. It's matt black so you can't see it too clearly on film and TV sets. It fits the matching black 451EB thingy and looks pretty good as well as offering high performance. The CK22 is a new version of the CK2 omni capsule for the 451, with improved wind- and pop-shielding. AKG Acoustics, (Contact Details); AKG Acoustics, (Contact Details).

Music and Movement


The Music Laboratory, famed for their excellent work keeping Revoxes in their normal state of excellence - not to mention most other pieces of equipment - appear to have become so successful (not surprisingly) that they've had to move out of their old premises in Lyndhurst Gardens, N3, to new, luxurious surroundings a mere stone's throw from London's best Indonesian restaurant and Euston Station.

The new location is fitted up with showrooms, service department and Music Lab's more recent addition, an equipment hire service (an excellent thought).

Music Laboratory provide an excellent service to the industry, and are well worth contacting if you need anything done in the pro and semi-pro studio equipment line.

Contact them at their new address: (Contact Details).

Comprehensive Cables


Lectriflex Cables and Accessories Ltd. tell us that they're now producing, along with their range of multicore cables, connectors and conduits, a new range of multicore individually screened cable systems for the entertainments industry. These were specifically designed to meet modern requirements in terms of better flexibility, more pairs per cable, better capacitance and other electrical properties and lower cost. The new cable thus designed is now available in 1, 2, 4, 7, 12, 20, 30, 50, and 100-pair form (phew!). Also available are special connectors for use with the new cable. Sounds interesting for all you PA and studio builders!

Lectriflex Cables and Accessories Ltd, (Contact Details).

Mix-it-Yourself


People ask us if we're going to tell you how to build a mixer. Well, we have projects for outboard gear in the pipeline (see SI 1) but mixers per se are pretty far in the future. But in 1970-71, our companion mag, Studio Sound, described a mixer designed by David Robinson, including PC boards. Although it was a few years ago, the PCBs and reprints of the articles are still available, from Q-Energy Solution Ltd, (Contact Details). So if you want to mix it yourself, you know where to start.



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Sound International - Copyright: Link House Publications

 

Sound International - Dec 1978

Donated & scanned by: Mike Gorman

News by Richard Elen

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