Sorry, I inadvertently deleted part of my message.

Anders Andersson wrote:
> When encoding the surround channel, do you HAVE to 
> phase-shift (+90/-90), or
> is it equal to doing (0/-180)?

Although, I am not sure, I believe it is Left=0 Right=+180(or -180).

> And do you have to use the Band pass filter when encoding the surround
> channel? 

No.
>
I guess every decent dolby-decoder uses a LP-filter 
> for that channel
> anyway.

Decoders filter and delay the surround channel. Most can also do other
things to the surround like EQ, mangle it with some sort of pseudo-stereo,
and/or add multitap delays or reverb. Just depends on the manufacturer and
what they think will sell.

> Do you HAVE to use some dolby noise-reduction for the 
> surround channel? 

It is in the format (encode/decode hardware). It is Dolby B, so is not *too*
obtrusive. Anyway, it is to overcome noisy distribution sources (VHS tape,
etc.).

If you really want the Dolby Surround format, output your four discrete
channels (L/C/R/S) from Csound, then encode it with Dolby hardware or
software such as the Pro-Tools plug-in.