Where the audio signal of centers back channels go in a 5.1 setup?

[FargateOne]

Hello,
I have read the owner manual and did not find the answer! I have a 5.1 system 2 fronts, 1 center,2 surrounds, 1 sub. When I playback a 7.1 source (BD player to the AVReceiver via HDMI connections), where goes the audio signal of channels 6 and 7? Those audio tracks are registered into the dvd no? Many receivers give the choice (in a 7.1 setup) to send these audio tracks to centerback speakers or front heights speakers.
In a 5.1 system where are they downmixed? Or, are they lost somewhere into the electronic of the receiver?? Is ther an industry standard for this downmixing operation? Or do Onkyo, Marantz, McIntosh, Yamaha, Rotel downmixe whatever they like? Is it possible that those audio tracks are "blended" with fronts left and right channels?

 

[Tony V.]

If you only have a 5 channel speaker setup then the 6th and 7th channels would be sent to the only two surround channels you have.

 

[Matthew J Poes]

Hello,
I have read the owner manual and did not find the answer! I have a 5.1 system 2 fronts, 1 center,2 surrounds, 1 sub. When I playback a 7.1 source (BD player to the AVReceiver via HDMI connections), where goes the audio signal of channels 6 and 7? Those audio tracks are registered into the dvd no? Many receivers give the choice (in a 7.1 setup) to send these audio tracks to centerback speakers or front heights speakers.
In a 5.1 system where are they downmixed? Or, are they lost somewhere into the electronic of the receiver?? Is ther an industry standard for this downmixing operation? Or do Onkyo, Marantz, McIntosh, Yamaha, Rotel downmixe whatever they like? Is it possible that those audio tracks are "blended" with fronts left and right channels?

Tony nailed it. There are standards. Manufacturers have and surround codec developers sometimes put out papers discussing this, but typically its not openly discussed much. It is certainly not lost, it is down-mixed. It is possible that there is more to the equation than simple down-mixing, but it is unlikely we will ever know without inside knowledge.

The standard for downmixing as I understand it works something like this (fed a 7.1 signal):
5.1 (rear surrounds mixed into side surrounds)
5.0 (LFE channel mixed into front mains and/or any speaker set to large)
3.1 (surround channels remixed into front speakers)-some devices have DSP processing to give the illusion of surrounds using this, same is true of a 5.1 setup
2.1 (center and surrounds is remixed into the L and R speakers)
2.0 (Center, Surround, and LFE mixed into L and R speakers)

In effect, no information is ever lost, it is just utilized to its fullest extent. If you can believe it, this remixing process is more complicated than it seems and not all systems handle it right. For example, remixing the LF's and LFE into the mains can increase the bass levels too much. This is compensated for so as not to overload the signal.

Bass management too can get goofed up and here it is far more common to see manufacturers mis-handle the remixing if they don't account for this use case. Imagine you set EQ to each speaker and then drop some of those speakers? Imagine the EQ is setup before bass management (it often is) and you have set EQ for each speaker separately. The remixed signal can combine the boost or cut, it compounds that. Now imagine that mono bass is sent and remixed to just the subs. This compounds the issue and causes the bass EQ to now be wrong. Too much boost or cut at a given frequency.