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Topic: How to properly downmix 7.1 track (DTS or FLAC) to stereo? (Read 4789 times) previous topic - next topic
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How to properly downmix 7.1 track (DTS or FLAC) to stereo?

Hi guys,

I'm a bit at a loss here. I've always downmixed 5.1 tracks using Channel Mixer in Foobar2000, but it seems it doesn't fit here.

I need some tool or a plugin, which can turn 7.1 track into stereo properly. I searched the internet but I haven't found any suitable variants apart from VST plugin from Waves (DTS Neural pack at exorbitant price).

Can anyone help, please?

Re: How to properly downmix 7.1 track (DTS or FLAC) to stereo?

Reply #1
Use "Downmix channels to Stereo" included with every version of foobar2000.

Trim levels for this component (which can't be changed) are -3 dB for Center and -3 dB for Surround (side & back).  -3dB for LFE.  Works pretty good.

Re: How to properly downmix 7.1 track (DTS or FLAC) to stereo?

Reply #2
Use "Downmix channels to Stereo" included with every version of foobar2000.

Trim levels for this component (which can't be changed) are -3 dB for Center and -3 dB for Surround (side & back).  -3dB for LFE.  Works pretty good.

Thanks a lot! I never thought that simple plugin was this advanced.

Re: How to properly downmix 7.1 track (DTS or FLAC) to stereo?

Reply #3
Use "Downmix channels to Stereo" included with every version of foobar2000.
Trim levels for this component (which can't be changed) are -3 dB for Center and -3 dB for Surround (side & back).  -3dB for LFE.
From my test it seems that "Downmix channels to stereo" in foobar2000 1.3.15 uses 0 dB for LFE. I created 7.1 file with all channels with level 0% (-∞ dB) except LFE  with level 100% (0 dB), then downmixed it to stereo using "Downmix channels to stereo" in foobar2000 1.3.15. Resulted stereo file has peaks 0 dB in both channels.

Re: How to properly downmix 7.1 track (DTS or FLAC) to stereo?

Reply #4
Use "Downmix channels to Stereo" included with every version of foobar2000.
Trim levels for this component (which can't be changed) are -3 dB for Center and -3 dB for Surround (side & back).  -3dB for LFE.
From my test it seems that "Downmix channels to stereo" in foobar2000 1.3.15 uses 0 dB for LFE. I created 7.1 file with all channels with level 0% (-∞ dB) except LFE  with level 100% (0 dB), then downmixed it to stereo using "Downmix channels to stereo" in foobar2000 1.3.15. Resulted stereo file has peaks 0 dB in both channels.
That's bad, after all, the LFE channel gets doubled, which gives it a total loudness increase of at least 3 dB. The standard -3dB volume change for center, lfe and rear center channel when downmixing exists with reason.

Re: How to properly downmix 7.1 track (DTS or FLAC) to stereo?

Reply #5
That's bad, after all, the LFE channel gets doubled, which gives it a total loudness increase of at least 3 dB. The standard -3dB volume change for center, lfe and rear center channel when downmixing exists with reason.

It might not be that big of deal with the LFE channel being mixed in like that in a lot of cases.  Music itself has very little reason to use the LFE channel for anything other than what movies themselves are supposed to use it for as all the other channels are very capable of carrying full bandwidth audio just fine.  Dolby themselves seems to recommend not including the LFE at all.  That said if you got a problem 5.1 or 7.1 mix you can mix it down using matrix mixer component instead.


Re: How to properly downmix 7.1 track (DTS or FLAC) to stereo?

Reply #7
From my test it seems that "Downmix channels to stereo" in foobar2000 1.3.15 uses 0 dB for LFE. I created 7.1 file with all channels with level 0% (-∞ dB) except LFE  with level 100% (0 dB), then downmixed it to stereo using "Downmix channels to stereo" in foobar2000 1.3.15. Resulted stereo file has peaks 0 dB in both channels.
Dolby themselves seems to recommend not including the LFE at all.
According to Dolby guidelines, the LFE channel should be discarded when downmixing:

https://wogwoe.com/Sounds/00_PapersLinksNotes/Dolby_Multichannel_Music_Mixing.pdf
5.1.2 The LFE Channel     
Since the reproduction of the LFE channel can sometimes be considered optional, essential low-frequency information should not be mixed exclusively to the LFE channel. In fact, in most downmixing situations, the LFE is completely disregarded.

http://www.associationdesmixeurs.fr/wp-content/uploads/2015/10/Dolby-5.1-Channel-Production-Guidelines.pdf
5.3.3 LFE Channel
What is the difference between the LFE channel and the subwoofer signal? The LFE channel is a separate, limited frequency bandwidth signal created by the mixing engineer and delivered alongside the main channels in the mix.
If no subwoofer is present, the bass (including the LFE channel, if it exists) is redirected to the speaker(s) best able to reproduce it, usually the main stereo pair.
Another benefit to using the LFE channel when carrying explosive bass signals is that smaller stereo systems may not be able to handle such high levels of deep bass without significant stress. Since the Dolby Digital downmix process discards the LFE signal, these low-frequency signals will not present any difficulty for these smaller systems. The remaining portions of the bass frequencies delivered by the main channels will convey the essential aspects of the performance when listening to the downmix.

Other related discussions:
https://hydrogenaud.io/index.php?topic=104214.0
https://www.audiosciencereview.com/forum/index.php?threads/lfe-in-a-stereo-downmix.27922/
https://www.avforums.com/threads/dolby-digital-on-2-channel-setup.2365274/#post-29351653