That's Matrix H, which is the most over complicated matrix encoding quad ever used. It was impossible to decode at all accurately with 1970s analogue electronics, and is still extremely difficult with modern computers. The BBC were definitely mistaken in proposing Matrix H.
This broadcast is in Matrix HJ, which was a combination of Matrix H and 45J encoding. This later morphed into UHJ which is a matrix encoding of Ambisonics which is still in use professionally. Doing the phase shifts and basic matrix decoding is easy with computers. The problem is removing the residual ubbish from the other channels, so that something appears genuinely in rear right rather than every speaker except front left. That's damned hard even with modern computers. -- Owen Smith <[email protected]> Cambridge, UK > On 3 May 2020, at 19:55, Dave Lambley <[email protected]> wrote: > > >> >> On May 3, 2020 2:28 PM Owen Smith <[email protected]> wrote: >> >> >> That's it, it was originally broadcast in Matrix HJ. As you say, not clear >> if the rebroadcast is matrix encoded but unless they've re-mastered it in >> some way it probably is. > > I've been admiring the diagrams and matrices in > http://downloads.bbc.co.uk/rd/pubs/reports/1977-02.pdf > > It looks rather phase sensitive. I'd fear that the psychoacoustic compression > on the iPlayer might harm that, but you never know until you try. You might > be better off searching for other sources of recordings though. > >> >> My friend develops his own matrix decoding solutions using multiple steps in >> off the shelf audio processing software, like Audacity. This is not remotely >> real time, it takes many hours to do one album. But if you're doing matrix >> decoding you can keep the output and listen to it again. He and I have never >> understood the general obsession with decoding matrix quad in real time. Do >> it well and do it once. > > Do share your results, I am curious. If the process is similar to the one in > the paper, it looks like the kind of thing modern CPUs can eat for breakfast, > if done in something compilable. The block diagrams are reminiscent of audio > codecs and software defined radio. > > I imagine you could do a better job of decoding it than was ever possible in > 1977. The rather cruder Dolby Surround system has been through multiple > revisions over the years. > > All the best, > Dave _______________________________________________ get_iplayer mailing list [email protected] http://lists.infradead.org/mailman/listinfo/get_iplayer
