Solved: Dolby ProLogic II downmix

[mtsonline]

Hi :-)
chat gpt didn't create any useful output - all commands had errors. But it was helpful to understand some impacts.
I added the 5.0 to be sure it does keep the five channels - you can change the output channe llayout to stereo if you like, it does not matter at all.
Or just leave it out, I had it only for testing included in the command and didn't remove it afterwards.

Also the input channels are corectly determined automatically - so the resample command alone will work.

important is just the phaseshift of the surround channels, if they are not already shifted (e.g. decode from ac3 or any movie source) or a five mic surround recording.
So if you create five indipendent channels in your production and you do not shift the rear channels you will get a slightly distroyed output.
In fact you will hear, that the front channels volume will lower down as soon as the rear channels get active. This is due to the two (respectively four) channels interfearing with eachother, as the decoder has problems to recognize the different channels without the shift.
cheers

[SeeMoreDigital]

Originally Posted by tebasuna51

It is not my opinion, see my posts.
But maybe it depend with how was generated the channels:

1) If channels was from a previously encoded 5.1 file (like in pool, AC3, DTS,...) the surround channels there are already phaseshifted and not need another phaseshift.

2) If surround channels was generated from front channels maybe need a phaseshift to avoid interferences.

To listen the output the AVR must have activated the DPLII decoder....

Thanks for supplying the (2-ch) Dolby Prologic 'channel check' samples in Dolby Digital. These are most useful additions to my sample collection

I do however have a cheeky request, do you have any (2-ch) Dolby Prologic 'channel check' samples in LPCM.wav?


Cheers

[tebasuna51]

Originally Posted by SeeMoreDigital

I do however have a cheeky request, do you have any (2-ch) Dolby Prologic 'channel check' samples in LPCM.wav?

Easy solution: decode the AC3

ffmpeg -i "dplii.ac3" -acodec pcm_s24le "sound_pan.wav"

To decode it to 5.1 you need a dplII decoder

[mtsonline]

Hi :-)

finally here is the result and a surround dplii encoded song where ffmpeg and the outcome of the discussions where used:

Stream and download Virtuality on ...


Amazon Music:

https://music.amazon.de/albums/B0CBK...sin=B0CBKCRL5D


Apple Music:

https://music.apple.com/us/album/vir...gle/1696588622


Spotify:

https://open.spotify.com/intl-de/tra...b7ee9d644e4384


cheers

Martin

[FranceBB]

Originally Posted by mtsonline

finally here is the result and a surround dplii encoded song where ffmpeg and the outcome of the discussions where used

Well, my 5.1 played it correctly with Pipewire/Wireplumber reconstructing the 5.1 from the downmix upon playback.
I couldn't really hear many effects outside of the normal stereo mode until I arrived at around 1 minute and I heard the "tap" coming from the side, so it worked.

(I know this must have a name, but I'm music illiterate, so I have no idea what instrument produced that sound xD)