What is the effect of converting multichannel movie Atmos/DTS to AAC?

2023-03-22 02:11:09

I have a massive collection of DVDs and Blurays that I am getting rid of, converting them to digital formats in my spare time. Many use Dolby Atmos, DTS-HD, Dolby 5.1, etc and I'm converting them to AAC. I would like to know the effects of this being played out of a hypothetical 7.1/atmos audio system or sound bar.

More technical notes: I'm using FFMPEG to rip the multichannel audio streams from my movie discs to WAV and then using QAAC to convert them to AAC, retaining all of the channels of audio in the new file.

Will an atmos/5.1/7.1/sound bar be able to play ALL of these channels properly or will I be missing something/something lost???
If so I may end up trying to retain the lossless audio but it will cost me quite a lot more disk space... OR just converting them to 2-channel stereo...

Thanks a lot for your replies, I really do appreciate your advice on the matter as I don't have my home theater setup to test this out yet and will not for another year.

Re: What is the effect of converting multichannel movie Atmos/DTS to AAC?

Reply #1 – 2023-03-22 03:01:57

If your setup supports Atmos, it's possible you'll lose something if the movie soundtrack was Atmos encoded.  When dealing with stuff like Atmos leave as is.  The same is true for DTS: X.

If it's regular Dolby Digital or DTS it's fine to convert it but keep in mind AC3 is already small and lossy to begin with and you could lose dialogue normalization and/or other DRC information if you use DRC on your receiver.  Best left alone.

Dolby TrueHD might benefit from being converted to AAC if space is a concern but I just use regular Dolby Digital if the soundtrack is 5.1 but again I just leave it alone.

For DTS-HD Master Audio you can keep only the core DTS stream if you want if space is an issue but again I leave it alone.

I strongly recommend you leave it as is unless space is a very serious issue.

Re: What is the effect of converting multichannel movie Atmos/DTS to AAC?

Reply #2 – 2023-03-22 15:01:43

Dolby Digital and DTS are already lossy compression.   Generally you should avoid lossy-to-lossy conversion because it introduces additional losses, even at the same bitrate.     But you may not hear any quality loss.    Conversion to AAC would only be an advantage if your player needs AAC or if you need smaller files (lower bitrate).

Converting/compressing the lossless files is probably "OK" but make sure the decoder/converter is handling Atmos downmixing correctly.

Of course, a soundbar doesn't really give you sound from behind or from the sides, and even the left/right separation isn't usually as wide as speakers.

If possible, I would recommend archiving the original format.      ...I have some 4TB hard drives with copies of all of my DVDs (and a couple of Blu-Rays) in their original format, including the video.   I use PowerDVD or VLC to play them.   (VLC doesn't properly support Blu-Ray).   I can play them on my computer or plug the HDMI into my home theater system.

Re: What is the effect of converting multichannel movie Atmos/DTS to AAC?

Reply #3 – 2023-03-23 03:03:03

I must thank you both for this. It has been enlightening!
I understand your warnings and suggestions but I will continue to go the AAC route for now. The size issues are quite severe at my scale.

I tested this out yesterday and this morning with a few of the most recent blurays I bought and some older DVD TV series and the after averaging out the size differences between them I realized I couldn't afford it sadly.

Thank you both for helping me make an informed decision on this.