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Michael Brown
Bradford Student Cinema
www.Bradfordstudentcinema.co.uk

For matrixed surround: Any signal present on the left and right sound track and in phase will be played through the centre channel.

Likewise, any signal on both left and right sound tracks, but in-anti phase (180 degrees) will be played on the surround channel.

The remaining audio information will be played on the respective left or right channel.

You should therefore notice that the vocals of a song, will usually come out of the centre channel because they are usually panned dead centre of a typical stereo mix with no phase shift between the left and right channels.

With a computer, an audio editing package and a Matrix decoder (your cp-55 or a hi-fi pro-logic effort will do) you can experiment with your own surround effects. Eg take a mono wave file, convert it to stereo, phase invert one channel and run it through a Matrix decoder and the sound will mostly come out from the surrounds. With a bit of patience you can create a home made surround mix.

In other words, the surround channel carries the stereo part of the mix and the centre channel carries the mono part, while the left and right channels carry the complete left and right signals respectively.

A normal garden variety stereo soundtrack contains lots of stereo information and this all gets sent to the surrounds. However, because vocals are mostly panned to centre they tend to be mono, so don't make it out to the surrounds, but there is usually some stereo reverb on the vocals so this does get into the surrounds.

The result is that the vocals can often still be heard in the surrounds but they are distant and echo-y because all you are hearing is the reverb.

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President
Panalogic Corporation Pty Limited
44 Carrington Road
Castle Hill NSW 2154
Australia
Phone: 61 (0)2 9894 6655
Fax: 61 (0)2 9894 6935

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As far as Dolby is concerned, since the CP-55 and onwards the offical "Non-Sync" format (format 60)...Left goes to left, Right goes to right (un-matrixed) and surrounds are derived via the 2:4 decoder.

On the Cat. 243 (logic card) there is a jumper to select the "magic surrounds" for non-sync or to turn them off (inhibit). The jumper jumps in the appropriate diode.

As Gord pointed out...with the CP-65 and the Cat. 443 the ability to decide between a true "2:4" decode (like for videotapes and such) or the standard "Non-Sync" format.

With the Cat. 441 (stereo surround card, needed for digital) one also gets an adjustable "Non-Sync surround" level trim pot to boost the level.

Remember, CDs and other stereo sources are mixed and monitored using a two-speaker system thus Dolby tried to recreate that as accurately as possible with their Non-Sync format with the "magic surrounds" as an option. I suppose this might be changing as now many homes have some sort of Pro-Logic decoding.

Steve