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Mixing 5.1 Audio with LD PCM

3 Replies, 899 Views

So I've got a couple of projects in mind where I will need to insert some additional footage from an extended version (which is 5.1 only) into the main movie for which I'm using 2.0 Laserdisc PCM (Dolby Pro Logic I). The first thing I need to do is convert the 5.1 to 2.0, in a manner that it gets unpacked the same way the Laserdisc PCM does i.e. DPL I. 

Chewtobacca previously detailed an avisynth script to convert to DPL1 and suggested that BeHappy could be used - it's an avisynth audio GUI.

So the first thing I did was convert the DTSHD 5.1 track to wav using eac3to. I then loaded that into BeHappy, selected Downmix DPL I and that gave me a 2.0 file. Interestingly there were several input methods, bassaudio, FFAudioSource and LwLibavAudioSource all produced identical sources, but WavSource produced a very different final third of the file so I used bassaudio. 

Anyway I know eac3to also has a DPL downmix option but it's DPL II not DPL I. So in order to compare I produced another file through BeHappy but this time DPL II and also produced one in eac3to using -downDPL.

What I did not expect was the results to be so different. So below, top is eac3to and bottom is BeHappy. Just to reiterate both of these are DPL II downmixes not DPL I. 

[Image: YIwM39n.png]

Anyone got any idea why these are so drastically different? Is eac3to maybe applying some kind of boost or normalisation? I just expected the two programs to produce similar results, if they are both using an industry standard method of downmixing i.e. DPL II?

I appreciate once I've decided on which option I'm using (I'm leaning towards BeHappy) I may well need to play around with the volume levels once I'm joining so it matches the Laserdisc PCM.
(This post was last modified: 2021-12-23, 12:49 PM by alleycat.)
It seems second is "only" leveled down... try to amplify it: find in Audacity what is the max level, and boost the second to the same; they probably have similar (if not equal) waveforms.
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Thanks spoRV, boosted to the same peak level it looks like this, now they look very similar. So think I'll stick with BeHappy as that has the option for DPL I. Cheers.

[Image: dKSQXdc.png]
(2021-12-23, 01:06 PM)alleycat Wrote: Thanks spoRV, boosted to the same peak level it looks like this, now they look very similar. So think I'll stick with BeHappy as that has the option for DPL I. Cheers.

[Image: dKSQXdc.png]

Using such diagrams it is impossible to determine the best sound quality, adding volume is not a problem, I usually use the best sound quality, even if it is stereo, and then you can work on processing it.

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