Composer and performer Lawrence Ball was presenting his synthesizer based works at a concert in a small concert venue. This turned out to be a way of getting both a Synthesized Stereo and a Synthesized Surround from a ‘Mono’ concert!

His pre-recorded stereo backing tracks, involving the initial ‘synth’ part of the compositions, were played into two channels of his PA mixer. His keyboard, for the ‘live’ part of his delivery went into two other channels – effects being added appropriately to either feeds. The ‘curious’ aspect, following the mix, was it was all ending up being heard by the audience from a single mono loudspeaker placed central stage, in the small concert room with sixteen seats for the audience.

I was commissioned to record the concert, monitoring in a separate room and had obtained the two channel final mix from his mixer, via two DI boxes giving me mic level balanced feeds. Lawrence had suggested that I should also ‘mic the room’, with whatever I liked, in front of the audience loudspeaker.

The DI feeds went in on channels one and two of my Edirol R44 SD card recorder (Pic. One). Via one of my DIY mic-pre boxes, the mics of my choice (and backup convenience, as I have two sets!) were a Sennheiser M&S rig of MKH40/30, cardioid and figure of eight. Their feeds ended up on channels three & four on the Edirol. The mic rig was couple of metres in front of the loudspeaker and pointing upwards with the idea of getting more ‘room effect’.

Mixing these two pairings out of the Edirol, with equal levels from each pair, proved to be something of a ‘stereo revelation’, considering the audience were themselves back in a 1940’s ‘mono’ era! Playing around with the Sennheiser feed part of the mix, quickly showed that the best ‘fiddle’ was to not actually decode the M&S pair, but to simply pan the Mid left and the Side to the right!

Monitoring on site, in the isolated separate room, revealed an amazingly unexpected stereo result with Sennheiser HD650 headphones. There was a very even spread of the soundstage, with something of a ‘binaural’ effect, no doubt due to the many random phase related differences being obtained by the ‘freaky’ use of an un-decoded M&S pair with the two feeds panned apart, left and right, plus the ‘room effect’ being obtained and then mixed in with the two channel ’music feed with effects’ from the composer’s mixer.

This was very satisfactorily confirmed with my usual ATC20 Pro active loudspeakers, back at base. One aspect with stereo I listen for, is finding ‘the speakers not really being involved’ and avoiding it all collapsing to mono when you move away to the sides of the ‘sweet’ spot. This very effectively proved to be the case.

Using a Frank Fox ‘The Box’ LED display showed no excess of ‘out of phase’ components and some times the wonderful ‘momentary holes’ in the display – this I have always recognised as being proof of a stereo feed worth listening to.

Summing up - obviously it is hard to get a ‘theory’ for what is going on, considering that the audience were just hearing a single mono speaker feed in that concert room, but the random phase and level variations in the mix from both of the feeds, so suiting ‘electronically’ generated music, would seem to encourage others to have a go and maybe take it further………………………….. !

THE DERIVED SURROUND

So, how about a Surround Playback from the four channels captured on the Edirol? Using my DIY 5.0 control system with a near to ITU five loudspeaker layout, and the essential DK Technologies ‘Jellyfish’ display and Bargraph level meters, it was easy to derive a way of getting an enveloping result where, when you mute the rear and centre feeds, it collapses to a very poor ‘stereo’ replacement.

The first thought was to have the DI mix as the front L and R feeds – the most direct sound. Then to use the two channels from the mic rig in Front of the loudspeaker as the Rear feeds. These provide the de-correlated feed needed for the Rears, with also their ‘room’ ambience pickup. It all comes over rather well! My usual remote control muting of the rear feeds, from the listening sweet spot, removes the feeling that you are ‘elsewhere’ when you collapse to the just the DI front ‘stereo’.

Having a vacant Centre channel feed brought up the idea of using the Mid mic pickup available from the left of the Rear feeds, to feed to the Centre speaker. After arranging this, with due regard to its phase relationship, I can report no problems. Muting the Centre channel does not interfere with what I am hearing and you feel you have the usual enhanced sweet spot focus point.

Final summary? Having variable width controls of the Front and Rear feeds, as well as having individual trimming of the levels of the L & R feeds of each, is a vital aspect of Surround ‘Post Production’. All related to what you hear, of course, but in my view, this is so vitally confirmed by what you see with the Jelly Fish display and its Bargraphs.