Surround

A mono or stereo source fills every front centre, low-frequency and surround speaker the device has, with one fixed matrix. For a stereo source with channels L and R:

• front left and front right: L and R, unchanged;

• front centre: 0.707 × (L + R);

• low-frequency channel: 0.5 × (L + R), through a 120 Hz low-pass;

• each surround pair, side or back: 0.5 × (L − R) on the left and 0.5 × (R − L) on the right. A 7.1 device plays this from both of its surround pairs.

A mono source with channel M plays M at unity from both front speakers, 0.707 × M from the centre, 0.5 × M through the low-pass from the low-frequency channel, and 0.35 × M from every surround speaker. A source with more than two channels is never upmixed, and a device without a front pair changes nothing.