any three channels with polarity reverse on one and the ability to pan will decode M/S (analog or digital)...when spend money on a dedicates matrix?

Formula:

M channel: Pan center.
S channel number one: Pan left; polarity normal
S channle mult( a copy or mult of the S channel): Pan right; polarity reversed.

So, M is up the middle and gives you your mono center/image. The Left S+ and right S- channels give you your stereo/side information.
Play with the balance, though the combined S+/S- channels can start around -3db relative to the M channel.

[ December 02, 2003, 12:28 PM: Message edited by: RecorderMan ]

Is that all there is to it?

Are there any benefits of a stand-alone matrix?

Thanks.

The only advantage I can see of a dedicated M/S decoder would be in a live-to-two situation, where you need to get the correct stereo imaging onto tape, rather than decoding it later during mixdown.

I've only used M/S a coupla times, but in both instances I decoded after the fact using three channels on the desk and hard panning/flipping polarity, as described above.

Here is a decent article on the subject along with some links for DIY decoder boxes.

http://homerecording.about.com/library/weekly/aa112899a.htm

For DIY decoder you can also check PAIA kit at:

http://www.paia.com/msdecode.htm