# 5.1 Rear To 5.1 Side mixing matrix

I am searching for a matrix definition for converting a audio signal (5.1 with rear) to a audio signal (5.1 with side). Currently I am using the definitions from: https://msdn.microsoft.com/en-us/library/windows/desktop/ff819070(v=vs.85).aspx. But I am missing the yellow marked matrices:

Does anybody has got an idea where to get it from? EDIT: Would be perfect if someone would have some other matrices else like quadrophonic,...

The commonly called 5.1 format uses only surround channels, which are defined as rear/side channels in ITU-R BS 775. The case you want to deal with (turning rear surround channels to side surround channels) is therefore not explicitly defined.

Notice that in the referenced ITU document, the case of changing the number of rear/sides loudspeakers reproducing a common rear/side signal is mentioned (see Note 5) :

If more than two rear/side loudspeakers are used, the LS signal should be fed to each of the side/rear loudspeakers on the left side of the room and the RS signal should be fed to each of the side/rear loudspeakers on the right side of the room. In doing so, it will be necessary to reduce the signal gain such that the total power emitted by the loudspeakers carrying the LS (or RS) signal is the same as if that signal had been reproduced over a single loudspeaker.

In your case, as you are keeping the same number of loudspeakers, I would simply map Rear Left (resp. Rear Right) to Side Left (resp. Side Right) with a gain of 1.0.

The case is different if you want to downmix a 7.1 format (of which several mappings are mentioned in ITU-R BS 2159, see figure 20) to a 5.1 format, where you will need to take into account which mapping is used in the 7.1 format to define downmix coefficients.

Also notice that although there are commonly used coefficients when downmixing multi-channels formats, most codecs use metadata sets to allow the content creator to specify it's own coefficients in order to preserve artistic intent (see Dolby Metadata Guide, part 4 for example).

• Also notice that although there are commonly used coefficients when downmixing multi-channels formats where can i find some of these "commonly used coefficients"? – Florian Jun 3 '15 at 7:19