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Why can I play 5.1 Multichannel files through headphones?

Discussion in 'Sound Science' started by beholdclarity, Oct 18, 2019.
  1. beholdclarity
    Hi fellow music lovers,

    I have a question which will determine the way I am going to listen to my SACDs in the future. My choices are:

    a.) The 5.1 mix or
    b.) the stereo mix

    I have been playing around with my setup and I can play 5.1 Multi-Channel files through the DAC of my MacBook connected to my Stax Energizer (which is an AMP only) just fine. The channels are all present and seem correctly placed.

    Only 7.1 is missing a couple of channels.

    What happens when a DAP like the SP1000 or even the internal DAC of a Macbook are faced with 5.1 mixes and feed that signal to a stereo out. I presume some kind of down mix?
    Is there a downside to using the 5.1 mixes or even an upside?
    Last edited: Oct 18, 2019
  2. bigshot
    It all depends. I've heard SACDs where the stereo mix was deliberately hobbled. In one, it was a much older mix than the 5.1. In others, the stereo is better than a 2 channel fold down of the 5.1 mix. I think you are just going to have to listen and decide for yourself. I put a post it on the covers of SACDs that need special playback settings and write down the best way to play them.
  3. beholdclarity
    Got that part, but let’s assum the 5.1 and stereo are the same mix.
    Any downside of my Astell kern downmixing the song for me?
  4. bigshot
    We could ask Gregorio, but my guess is that the stereo and 5.1 mixes are usually separate mixes optimized for the format
  5. gregorio
    That depends on how your Astell unit is downmixing. Most downmixing assumes the 5.1 is film sound rather than SACD, which is different to film sound, so it depends exactly what your Astell is doing and what the engineers who mixed the SACD did.

    I would think the stereo and 5.1 versions on an SACD are generally not the same mix. I would generally think it’s better to play the stereo mix on the SACD, rather than a downmix by your Astell but as bigshot mentioned, that’s probably not always going to be the case.

  6. beholdclarity
    In conclusion: it depends.

    Thanks for your responses :)
    ParaLoganGrado likes this.
  7. gregorio
    If we're going to give an accurate answer then we have to cover all eventualities, because it's often the case, even with physical properties, that an absolute answer is only true with conditions. The absolute statement that audiophile cables make no audible difference is a good example, the statement is true but there are some very specific conditions where it would not be true (most of which should be obvious). In this case though, we're not talking about properties/performance constrained by the laws/rules of physics but about a creative, practical and/or marketing decision that someone has taken. For example, it's possible that the stereo version has been mastered for playback under poor listening conditions, has therefore been more heavily compressed and could sound worse than a downmix of the 5.1 mix when played back under decent/good listening conditions. Furthermore, this practical decision is often marketing driven, to demonstrate an audible improvement of one (higher priced) format over another. This is relatively common with "hi-rez" verses CD versions but obviously not so necessary (for marketing) in this case because we already have the pretty obvious audible difference of 5.1 verses stereo and therefore it would be far less common.

    If you need a single rule/answer, then because of the above I would say play the stereo version from the disk, rather than downmixing in your unit, as usually you'd either get the same or a better result. Just be aware that occasionally you might get a worse result.

    Chris Kaoss likes this.
  8. beholdclarity
    Hi G,

    I hope I did not come across as ungrateful. I was expecting the answer you gave but lacked the experience and knowledge to verify it for myself.

    I compared the multi channel and stereo layer of my Wish You Were Here SACD and found that the multi channel is roughly 6 to 9 dB louder in audacity. Matched to volume, the stereo has some detail in the distance that multi channel lacked (on a stereo stystem, that is!!!). But the multi channel has a bit more energy, perhaps due to compression (the compression doesn’t seem too bad, but rather the stereo layer very quiet)
  9. bigshot
    That volume difference is very common. Human ears naturally tend to think louder sounds have higher fidelity, even if the softer sound is identical. That is a psychological trick to make consumers think the multichannel or "high definition" audio sounds better than plain vanilla CD sound. I see that all the time on movie blu-rays too. The principle advantage of multichannel sound is having more channels, not sound fidelity. A lot of the perceived sound quality depends on how good the mix is. The format has very little to do with that.
    Last edited: Oct 23, 2019
  10. gregorio
    1. No problem, I didn't take it that way.

    2. That would depend on how audacity is measuring and downmixing it. 6 channels of audio mixed to 2 channels at unity gain is going to be higher level than just a 2 channel mix, 6-9dB being likely. As a 2 channel mix will usually hit 0dBFS, then 5.1 downmixed (at unity gain) would pretty much be guaranteed to severely clip. For this reason the downmix is never at unity gain, commonly it would be left and right -3dB, centre -6dB, surrounds -6dB (or -9dB) and LFE at least -10dB or commonly discarded entirely. Typically you'd end up with both mixes roughly in the same loudness ball park so audacity is maybe doing something a bit unusual, maybe compressing the downmix to below clipping rather than having a lower level. This is the reason why, even if the stereo mix on the disk is just a downmix, that your probably better off playing that.

    3. I would expect what you observed, a dedicated stereo mix to have a bit more detail than a 5.1 downmix. Usually, there are periods in the music where there is only surround ambience in the rear channels, mixing this with the ambience already in the left/right channels will just muddy up the stereo downmix but with a dedicated stereo mix, the engineer would recognise this occuring and lower the level of the surround channels being mixed to the left/right at such times (or remove them entirely). There are other situations like this or indeed the reverse, where the information in the surrounds needs to be higher than the default. This is the main reason why you should be much better off playing a dedicated stereo mix from the disk.
    3a. Unless there's been some serious error the stereo layer on the disk is the correct level and the downmix is too loud, but of course you might prefer that to just turning up the volume of the stereo mix.


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