New! BBC Matrix H quadraphonic


Matrix H was developed by BBC engineers in the late 1970s to carry quadraphonic sound via FM radio in a way that would be most compatible with existing mono and stereo receivers.

Few recordings were officially released in Matrix H, but the BBC organised, in all, a twenty month-long series of broadcasts of all genres from August 1976 to April 1978 in the format and many amateur recordings exist of these broadcasts.

See this page for a list of the broadcasts made by the BBC in Matrix H.

Essentially another phase-amplitude matrixing technique, Matrix-H may be thought of as QS with added rotation; a sort of hybrid of Sansui QS and CBS SQ. This fusion is justified by the argument that a certain "phasiness" in the front (stereo) image was a tolerable price to pay for the lack of cancellation of rear images for listeners with mono radios¹. Such a consideration was important for a national broadcaster - especially in the 1970s.


Decoding Matrix H

Stereo Lab (version 3.1.14 and above) provides accurate decoding of BBC Matrix H recordings so that they can be played over a modern 5.1 system - as defined in ITU-R BS 775 (although better results are obtained if the angle between the surround loudspeakers is reduced).

The encoded input file should be Matrix H encoded, two-channel stereophonic derived from the LP or tape replay (or other source). The output may be selected to be separate mono files (useful if you want to re-encode in DTS for example), as a group of stereo files encoded:

Or the output may be encoded as a multi-channel, 5.1 file. Note that, because these signals are quadraphonic (four-channel), the Center and LFE channels are silent.

"As long as the Matrix exists, the human race will never be free."

Whilst we don't need to go as far as Morpheus, it's probably true to say that what the quadraphonic market didn't need by 1976 (the date after which both the major record companies and the electronics giants were bailing-out of the sickly quad' market²) was a further, incompatible quadraphonic system.

Introduced into Britain by the BBC just as the country's post-war planned-economy project was running out of steam and the country was poised to slump into recession and the winter of discontent, the tale of Matrix H is a Kafka-esque story of incomprehensible bureaucracy.

This is visible in the starkest terms in that, despite the BBC's efforts on the engineering and production side, Matrix H was denied a listenership because no commercial decoder was available for these broadcasts - at least at the start of broadcasting³.

There exists an almost surreal clipping from the Radio Times magazine in April 1977 (right), written by the BBC's Chief Engineer Radio Broadcasting showing the delighted radio listener how to enjoy these BBC quadraphonic broadcasts. Our carefree (male) listener is told to connect his radio to his quadraphonic system via a shadowy, grey box labelled Matrix-H decoder - a device which didn't exist and which our radio enthusiast couldn't have bought even if he wanted to!

Matrix-HJ

The final chapter of the Matrix H story is its fusion with the System 45J from the Ambisonics team. At best this was a marriage of convenience. (Contemporary accounts speak of the hostility between the BBC Matrix H and Ambisonic teams7.) The National Research and Development Corporation - the quango established by the British Government to transfer technology from the public sector to the private sector - must have, by this time, been searching hard for somewhere they could land their seven years of investment in Ambisonics before the quadraphonic market collapsed altogether. And, as we have seen, the BBC was desperately in need of decoding technology to make its efforts on the production side worthwhile.

Matrix H had been derived largely from empirical work by the BBC, whereas System 45J had largely been born of theoretical work. Michael Gerzon, Ambisonics principal architect spoke of "40 pages of mathematics..." 6, to derive the System 45J's parameters.

Happily, despite their different rational vs. empirical origins, System 45J and Matrix H converged toward almost identical designs. So similar that it would only have taken a few simple modifications to a Matrix H encoder to make it into a System 45J encoder. In practice, it is impossible to tell if a recording is encoded in H or HJ as small production or reception changes (for example, the choice of different microphones, or an error of 20° in the phase of the recovered subcarrier in the stereo decoder) would easily change the encoded performance more substantially than the change in encoder. David Mears of the BBC (and joint author of the original Matrix H EBU paper)¹ is quoted as saying that, although he had not put pen to paper on the effect, he couldn't tell the difference between an HJ encoding and an H encoding through an H decoder 7.

We agree with that, and there thus appears to be no necessity to offer a different decoder for BBC Matrix HJ. If you disagree with this, please get in touch with us. It would not be difficult to add an Matrix HJ decode option.

The tragedy of the story of Matrix H (HJ) is that the sytem worked well, and the BBC radio productions (including pretty much an entire Henry Wood Promenade season) provided a wealth of material in the format.

As far as we are aware, Stereo Lab is the only commercial decoder³ ever available for this quadraphonic format..... Just 42 years late! Pspatial Audio would like to acknowledge Martin Pipe for the motivation for, and help with, the development of the BBC Matrix H decoder.

Demos

These two demos are from the album Instructions For Angels by the British composer David Bedford which is which one of very few albums released in the UK in Matrix H quadraphonic. It was the first album of an abandoned series of quadraphonic albums planned by Virgin Records. The sixth variation of the piece, this excerpt features a guitar improvisation by Mike Oldfield. The original Matrix H signal is decoded to a multitrack FLAC file. You will probably need to download this file and play in a multichannel application (like Audacity) unless your PC is configured for multichannel sound. (Some browsers will not play FLAC files).

The second example is from the fifth variation entitled First Came The Lion Rider. This excerpt features a steady rhythmic figure (in 5/4 time) played on piano and bass-synth in the front two channels with the two alternating sythesiser melody lines in each of the rear speakers. The original Matrix H signal is decoded to a multitrack FLAC file. Once again, you will probably need to download this file and play in a multichannel application (like Audacity) unless your PC is configured for multichannel sound. (Some browsers will not play FLAC files).

Matrix H (HJ) to stereo

There was some contemporary criticism of the stereo compatibility of BBC Matrix H, especially of some of the 1977 Prom season concerts7. The BBC issued a statement that Matrix H which conceded that stereo broadcasts, once claimed to be "completely unipaired" (see Radio Times article above), could no longer be described in those words7.

From our point of view, there is some justification in these criticisms: it is true that Matrix H encoded signals do sound a bit "phasey" in stereo. In fact, the mono compatibility of Matrix H is rather better than its stereo compatibility. BBC Radio 2, 3 and 4 had only been converted to stereo broadcasting in 1973, and and thus the BBC's principal concern must have been for the installed base of listeners in mono who must have far outnumbered stereo listeners a scarce four years later.

It's possible greatly to remove the "phasey" quality of Matrix H recordings in stereo by using the Stereo Lab decoder to decode to front-pair only. Obviously, there is loss of the rear information in so doing, but this can be an advantage too as there is often rather too much ambience in the quadraphonic signal.



UMX, BMX and UD-4

UD-4 was a discrete four-channel quadraphonic sound system for phonograph records. It was introduced by Nippon Columbia (Denon) in 1974. Only about 35 to 40 LP album titles were encoded in this format, and it was marketed only in the UK, Europe and Japan. Most of these releases were marketed by the Denon label.

The UMX standard4 used for UD-4 records contains two subsystems, BMX, a basic 4-2-4 matrix decoder, and QMX, extra information encoded on a high-frequency subcarrier (somewhat like JVC's CD-4) to enhance directional resolution.

Michael Gerzon pointed out5 that Matrix H will decode existing BMX discs (e.g. the UD-4 discs of Nippon Columbia) with reasonably accurate results. So, use Matrix H decoding if confronted with one of these rare quadraphonic discs.

UD-4 discs have very poor stereo compatibility (see Matrix H (HJ) to stereo section above). Therefore, even if a quadraphonic dub is not required of a UD-4 record, the Stereo Lab Matrix H decoder may be used to generate a good stereo version by decoding to the front-pair only.


References and Notes

1. The development of a compatible 4-2-4 quadraphonic matrix system, B.B.C. Matrix H. D.J. Meares and P.A. Ratliff, E.B.U. REVIEW No. 159 - OCTOBER 1976

2. Rogers in Diffusion of Innovation (New York: Free Press 2003) tells us that by 1975 quad equipment sales were only running at 5% of hi-fi sales and that the number of quadraphonic recordings never got close to 5% of the titles available on the market. By 1975, the record companies that had offered four-channel products began dropping them, and stereo equipment retailers began selling off their inventories at a discount.

3. There was a kit decoder made available from a BBC design published in Wireless World magazine: Purpose-built Matrix H decoder. Shorter, G. Wireless World, June 1977. But this was very impractical with nothing but the chipset from Sansui and extra boards for the modifications to a Variomatrix QS decoder on separate PCBs. There can't have been many constructors.

Better, was the NRDC-AMBISONIC decoder (designed by Michael Gerzon) which featured BBC Matrix H as one of its (many) decoding options. This too was a kit, produced by lntegrex Limited of Burton-on-Trent, after the design was published in Wireless World magazine in July and August of 1977. Whilst a complete kit, this was a complicated device to put together (and very difficult to test). It cost 45 without purchase tax in 1977: a lot of money. It could only have been available to very few people and the design emerged very close to the end of the BBC experiment.

4. Discrete-Matrix Multichannel Stereo. D.H. Cooper & T. Shiga, Journal of the Audio Engineering Society JUNE 1972, VOLUME 20, NUMBER 5. QMX used a 22kHz carrier with sidebands ±4kHz to enhance the directionality of audio frequencies below 3kHz. UMX/BMX stereo playback left a lot to be desired because of a 90° phase-shift between left and right stereo signals.

5. Variomatrix adaptor for System 45J and Matrix H. Gerzon, M. Wireless World, May 1977

6. NRDC surround-sound system. Gerzon, M. Wireless World, April 1977

7. Matrix HJ; technical refinement and political jostling? Wireless World December 1977 p.77


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