Audio: Surround to Stereo conversion tips

[MelCooley]

The usual apologies ("If this has been answered, sorry about that, just didn't see it", etc.)

I am feeding an mkv movie into Hybrid with 5.1 surround.  With some past conversion tools, the resulting stereo audio would not contain every track of all the channels.  For example, everything would sound fine until I randomly found a line of dialog that was just silent...maybe it was on the center track and wasn't picked up by the encoder?

My question is: What is the best setting to "dumb down" Surround audio to a simple L and R stereo track that doesn't drop any of the channels?

(Selur, I have high hopes for Hybrid!  Only just discovered it this morning, but it looks like it's going to the magic "fix all" tool that does everything.  Thank you!)Please, read the 'Infos needed to fix&reproduce bugs,..'-sticky before you post about a problem.

[Selur]

Here are the downmixes Hybrid offers from 5.1 to Stereo and how the channels are mixed:

• toStereo: "1v0.3694,3v0.2612,5v0.3694 2v0.3694,3v0.2612,6v0.3694"
  
• toStereo (dpl): "1v0.3205,3v0.2265,4v0.2265,5v0.2265 2v0.3205,3v0.2265,4v-0.2265,6v-0.2265"
  
• toStereo (dpl2): "1v0.3254,3v0.2301,5v0.2818,6v0.1627 2v0.3254,3v0.2301,5v-0.1627,6v-0.2818"
  
• toStereo (lfe): "1v0.2929,3v0.2071,4v0.2071,5v0.2929 2v0.2929,3v0.2071,4v0.2071,6v0.2929"
  
• toStereo (dpllfe): "1v0.2613,3v0.1847,4v0.1847,5v0.1847,6v0.1847 2v0.2613,3v0.1847,4v0.1847,5v-0.1847,6v-0.1847"
  
• toStereo (dpl2lfe): 1v0.2646,3v0.1870,4v0.1870,5v0.2291,6v0.1323 2v0.2646,3v0.1870,4v0.1870,5v-0.1323,6v-0.2291"
  

the syntax used to describe the downmix the syntax used by sox which is easily to understand
The source channel order is always the wave channel order. (Audio get's converted to wave, filtered and then converted to the target format.)

Looking at 'toStereo (dpl)': "1v0.3205,3v0.2265,4v0.2265,5v0.2265 2v0.3205,3v0.2265,4v-0.2265,6v-0.2265" we have:

• Channel 1: "1v0.3205,3v0.2265,4v0.2265,5v0.2265"
  
• Channel 2: "2v0.3205,3v0.2265,4v-0.2265,6v-0.2265"
  

So channel 1 is a mix of channels 1,3,4,5 and channel 2 is a mix of 2,3,4,6, where:
4v0.2265 means that source channel 4 is added to the mix with a volume of 0.2265.
and
4v-0.2265 means that source channel 4 is inverted and added to the mix with a volume of 0.2265.
-> As you can see each downmix used by Hybrid contains all channels.

Hybrid also offers the user do define their own downmixes in case you are not happy with the typical standard 5.1 to stereo downmixes offered through Hybrid.

Cu Selur

Ps.: if you are interested in audio filtering and what is done in Hybrid you might want to read the sox documentation (http://sox.sourceforge.net/sox.html) since Hybrid uses sox for audio filtering.