Advice on Converting 5.1/7.1 to 2.1

[rimmi2002]

Hi,

I recently switched my system from 5.1 to 2.1 with Anthem STR for Preamp / Buckeye Purifi 2CH AMP + ATV/Panasonic UB420 as main media sources. Overall I am very happy with it. I listen a lot to foreign music videos. The bass in the ones I have in 2.0 Audio sounds awesome, but I have many in 5.1 format and the bass is very much muted on them compared to before. Upon researching further it seems like when I have my ATV sends out a stereo signal from the 5.1 videos, it does not mix the LFE channel into the FL / FR 2.0 Downmix.

I figured atleast for my local media, perhaps I can get the 5.1 music videos songs to sound better if I remix it myself from 5.1 to 2.0 and include the LFE channel. With help of Gemini AI, I got the two lines below on how to covert my media with FFMPEG.

FFMPEG script for 5.1 --> 2.0 Conversion with LFE channel included at 1.0 Volume.

ffmpeg -i "input_file.mkv" -map 0:v:0 -map 0:a:0 -af "pan=stereo|FL=0.707*FC+0.707*FL+0.5*SL+1.0*LFE|FR=0.707*FC+0.707*FR+0.5*SR+1.0*LFE,aresample=resampler=soxr,volume=0.9" -c:v copy -c:a flac "output_stereo_lfe.mkv"

FFMPEG script for 5.1 --> 2.0 Conversion with LFE channel included at +10dB Boost to account for -10dB Attentuation
ffmpeg -i "input_file.mkv" -map 0:v:0 -map 0:a:0 -af "pan=stereo|FL=0.707*FC+0.707*FL+0.5*SL+3.16*LFE|FR=0.707*FC+0.707*FR+0.5*SR+3.16*LFE,volume=0.8" -c:v copy -c:a flac "output_with_boost.mkv"

Just wanted to get some input from real people with real experience, whether this is the best way to go.

1) Do you advice mixing the Surround channels in there? Or Should I just mix FL/FR with CEnter and LFe?
2) Anyone know how does ATV do it Multichannel to 2.0 algorithm?
3) Should I apply the +10LFE boost in the downmixing or is that not advised?

Thanks in advance.

 

[DVDdoug]

Most DVDs, Blu-Rays, and other sources have a stereo track that you can select. That might be better than a downmix but you're not going to get the full bass impact without the "point one" channel.

It looks OK to me with the 10dB boost.. Downmix Tables

In the real world you may have to bring the levels down (or normalize) so the mix doesn't clip. Overall, you are making it "louder" than the left & right alone. (I've never used the FFmpeg command line so I don't know how to do that.)

it does not mix the LFE channel into the FL / FR 2.0 Downmix.

That's technically correct. The other channels contain the "full regular bass" but the "extra" LFE channel isn't normally included in the downmix.

Or Should I just mix FL/FR with CEnter and LFe?

If you are batch processing you should probably include the surround channels in the standard way, except that you want to include the LFE. If you are downmixing carefully by-ear you can do whatever you want!

 

[Fslag]

hearing 2ch after going from 5.1 I don't know how someone can be happy with less sound.

 

[rimmi2002]

hearing 2ch after going from 5.1 I don't know how someone can be happy with less sound.

I thought the same until I heard a good 2.1 setup. My speakers create a much better sound stage with just 2 of them. Phantom center is great. Vocals are better than with my center channel. Do not miss the surrounds at all. Much easier to calibrate given there are only 2 speakers and the sub to deal with. Try it once. I was a non believer until I heard how well 2.1 sounds with proper speakers / amp / preamp.

 

[rimmi2002]

Most DVDs, Blu-Rays, and other sources have a stereo track that you can select. That might be better than a downmix but you're not going to get the full bass impact without the "point one" channel.

It looks OK to me with the 10dB boost.. Downmix Tables

In the real world you may have to bring the levels down (or normalize) so the mix doesn't clip. Overall, you are making it "louder" than the left & right alone. (I've never used the FFmpeg command line so I don't know how to do that.)


That's technically correct. The other channels contain the "full regular bass" but the "extra" LFE channel isn't normally included in the downmix.


If you are batch processing you should probably include the surround channels in the standard way, except that you want to include the LFE. If you are downmixing carefully by-ear you can do whatever you want!

Thanks.

The downmix table link is great.

I'll look through my media again, but from the few discs I have tried, that all have a DTS-MA or D. Atom track +5.1 DD track, but not all have a 2.0 track and for some that have 2.0 track, it is commentary or something else....I haven't experimented with movie tracks so much, but I am hoping Panasonic UB420 will do a better job on coverting movies to stereo than ATV, but if they all have a dedicated 2.0 track then nothing like it!

 

[Chrispy]

I thought the same until I hear a good 2.1 setup. My speakers create a much better sound stage with just 2 of them. Phantom center is great. Vocals are better than with my center channel. Do not miss the surrounds at all. Much easier to calibrate given there are only 2 speakers and the sub to deal with. Try it one. I was a non believer until I heard how well 2.1 sounds with proper speakers / amp / preamp.

Not sure if I had a good multich setup why I'd want to reduce it to 2.1 (2.2 in your case?). Could be room, your use, a few other things. Believing, tho?