Live Surround

E-mail conversation with Stefan Fuhrmann, (Ilmenau, Germany)

> Fuhrmann: Did you ever do a surround mix for the audience of a concert?
> (everything utilizing more than 2 channel stereo counts as surround)

Yes, I just put on a festival which featured several concerts of surround (both 8 channel and 5.1).

Also, I have often used a sort of pseudo 4 channel, in which the stereo signal is sent to a left/right pair of speakers at the rear of the space as well as to the usual left/right pair at the front. The time arrival differences, while technically "wrong", actually accentuate the stereo material, so in electro-acoustic music, with lots of panning, the effect is exaggerated movement and actually a type of surround.

> Fuhrmann: If not, why? (lack of interest? too expensive? technical reasons?)

Surround is the best, but there are several technical problems. With "live" electronics, meaning that the electronics are being performed in some way, not simply played back, there is the problem of computer audio outputs. The standard laptop has a stereo headphone output that is usually routed through a Direct Injection box to balance the signal.

Multi-channel requires either an audio card (PCICMA) or an external DAC. Some laptops (my 12 inch Powerbook for example) do not have any expansion slots, and there are major latency problems with many (most?) firewire or USB external DACs -- so for real time performance, where the action must be instantaneous, the headphone output is most dependable -- but only 2 channels! The other problem with external converters is their physical size, which is another chunk of electronics to drag onto the the airplane when travelling around.

> Fuhrmann: If yes, what are the biggest problems? (I can image, the Sweet Spot
> thing could be critical, because the people always sit everywhere but in
> the middle. Another thing may be difficulties in doing live surround
> panning for several sound-objects at once)

The sweet spot is a big problem for anything except mono - so we just ignore that (it is just as big a problem with 2 channel stereo).
The production end is easy regarding surround panning, though "live" panning would require special performance interface, like a joy stick -- but the biggest problems are those I mentioned above:

• latency on firewire & USB devices
• lack of outputs on the laptops
• portability

plus another:

• a standardized surround sound reinforcement system (5.1 is becoming a standard, but many avant garde works use 8 channels)

Hope that helps -- surround is cool, but I think we are a still a little ways off from doing it easily -- however I anticipate that latency problems will disappear with firewire 800 and faster CPUs.

> Fuhrmann: How could one try to circumvent these? (Using stereo only is not an
> option.)

• Actually, there is "diffusion", a well established technique since the 1970's, in which a standard two channel mix is "diffused" in real time through a proprietary "Loudspeaker orchestra", which has multiple channels for routing the stereo mix, from 4 to 32 (and beyond!) pathways, and through which a performer manually "plays" the spatialization in real time. This is actually very effective.

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