DIY Dolby surround

[Jay Martin]

Dolby is fairly simple to "simulate" without having to license anything.
Dolby surround is essentially this; signals that are "far right" or "far
left" are sent to the rear channel with a slight (usually 30 milliseconds or
less) delay.  In Pro-Logic there is also some "steering logic" that guesses
whether the sound was meant for right or left rear and also a simple
bandpass filter for the center channel.  To encode a "rear" channel that
Dolby could decode, all that would be necessary is to place the frequency at
one of the channels and a 180 degree out of phase signal on the other.  If
the level of the out of phase signals is the same, the Dolby unit will send
the entire signal to the rear.  Varying levels change the positioning
correspondingly.  An inverting op-amp or simple unity gain inverting
amplifier could be used to "encode" a rear channel!

Jay Martin
Interface Systems,
CLEO Technical Support.




> -----Original Message-----
> From:	Roman Sowa [SMTP:rsowa at WizjaTV.pl]
> Sent:	Friday, October 02, 1998 6:37 AM
> To:	synth-diy at mailhost.bpa.nl
> Subject:	ODP: DIY Dolby surround
> 
> it is done the analog way
> http://products.analog.com/products/info.asp?product=SSM2125
> *but* you must be 
> "licensee of Dolby Licensing Corporation, San Francisco, California"
> to use this chip
> 
> Roman
> 
> 
> > -----Oryginalna wiadomość-----
> > Od:	jorgen.bergfors at idg.se [SMTP:jorgen.bergfors at idg.se]
> > Wysłano:	2 października 1998 10:39
> > Do:	synth-diy at mailhost.bpa.nl
> > Temat:	DIY Dolby surround
> > 
> > Hi DIYers.
> > 
> > Do anybody of you know anything about coding for Dolby Surround? Would
> it
> > be 
> > possible to do with analog synth circuitry? It would give a new
> dimension
> > to a 
> > Leslie simulator, wouldn't it? Or maybe a surround panner. Any ideas?
> > 
> > /Jorgen