2016-07-15, 10:54
Just wanted to add a summation for others doing a search on this issue that ends here, to record my own conclusions, and why, after a period of indignation and high dudgeon on the IRC channel at a perceived backward move I've decided to relax and agree it's all good after all:
Firstly, it's worth pointing out, and remembering that those of us who had Sync Playback to Display on with passthru enabled, and were happy with it, have been experiencing a loss of quality all this time. It was compensating for the timing errors by dropping and/or duplicating the audio. Yes, many of us never noticed and were happy with it, but still, it was happening. We're not falling from an actually perfect situation here.
Now, I'm among those with a nice-but-older amplifier with only S/PDIF available for multichannel output. At first it seemed that this change downmixes everything into stereo PCM, which of course is unacceptable, but in fact you just need to enable the AC3 transcoding option in audio settings under passthrough audio, and then this change transcodes into AC3 5.1 at 640Kbit.
That is a lossy conversion. The question is, can you really perceive the difference? It's almost impossible to test these things definitively without double-blind conditions, as our perceptions are so mucked about by our confirmation bias, unless the quality loss really is very severe. Theoretically you may hear the difference, just as theoretically you might hear the effects of dropped/duped audio. It's certainly plausible that even on S/PDIF we're talking about exchanging one imperceptible loss of quality for another.
My guess is that you actually would be able to tell the difference, but probably only in certain testing passages in perfectly mastered material, and depending much on your listening conditions. Most of the time it'll be fine, and if you're really that discerning, or at least imagine that you are, you're probably a target market for a new AVR with HDMI inputs allowing multichannel PCM.
Which I may be in the future. Another reason to go there anyway is to be able to connect devices without S/PDIF outputs, like the new Apple TV, or a NUC-based HTPC.
So my next concern was that, I thought this change meant that even on a HDMI-only setup there would be a bitrate-reducing transcode, thus wiping out all the benefits of getting such a new AVR. I didn't want to buy such an AVR to end up with worse audio quality than I get now. But my understanding now is that this isn't the case.
I already understood the point, made earlier in this thread, that there is nothing inherently lower-quality about PCM, compared to passthrough of DTS-HD MA, TrueHD or any other lossless format (except the metadata issue with very new formats, which I'm not going to go into). Whether the decoding of the source happens in Kodi or in the AVR, it should make absolutely no difference to the resulting audio. The digital-to-analogue conversion is still done in the AVR, and that's where their quality can make a difference. (I wonder if some people's reluctance to let go of passthrough is a confusion between the digital-to-analogue conversion and the lossless, digital decode from an encoded bitstream to PCM?)
With this change, my understanding is that the audio from the source is decoded to a waveform which is then resampled to the outgoing PCM stream at the adjusted speed. This is all happening at 24-bit 96KHz, so while that resampling may be very slightly lossy, it really is all happening at a resolution way, way beyond our ability to hear it. Your cat may be able to hear it, but she won't tell, and she probably doesn't like it when you play stuff loud anyway. The lossiness to worry about is during compression to a lossy format such as AC3, and that isn't happening here (unlike with S/PDIF output).
In either case, though, starting from a lossless source probably does make a difference. In the HDMI + Multichannel-PCM scenario, this means that the lossless stream is the basis of the resampling. In the S/PDIF + AC3-transcode scenario, it's still always better to transcode from the best available source. So while, thus far, I've ripped my blu-rays without the lossless formats because I could only pass-through DTS-Core or AC3 to the amp anyway, it may actually now be worth having the lossless tracks there, for Kodi to transcode from.
But again, whether I'd really hear the difference is still questionable!
Firstly, it's worth pointing out, and remembering that those of us who had Sync Playback to Display on with passthru enabled, and were happy with it, have been experiencing a loss of quality all this time. It was compensating for the timing errors by dropping and/or duplicating the audio. Yes, many of us never noticed and were happy with it, but still, it was happening. We're not falling from an actually perfect situation here.
Now, I'm among those with a nice-but-older amplifier with only S/PDIF available for multichannel output. At first it seemed that this change downmixes everything into stereo PCM, which of course is unacceptable, but in fact you just need to enable the AC3 transcoding option in audio settings under passthrough audio, and then this change transcodes into AC3 5.1 at 640Kbit.
That is a lossy conversion. The question is, can you really perceive the difference? It's almost impossible to test these things definitively without double-blind conditions, as our perceptions are so mucked about by our confirmation bias, unless the quality loss really is very severe. Theoretically you may hear the difference, just as theoretically you might hear the effects of dropped/duped audio. It's certainly plausible that even on S/PDIF we're talking about exchanging one imperceptible loss of quality for another.
My guess is that you actually would be able to tell the difference, but probably only in certain testing passages in perfectly mastered material, and depending much on your listening conditions. Most of the time it'll be fine, and if you're really that discerning, or at least imagine that you are, you're probably a target market for a new AVR with HDMI inputs allowing multichannel PCM.
Which I may be in the future. Another reason to go there anyway is to be able to connect devices without S/PDIF outputs, like the new Apple TV, or a NUC-based HTPC.
So my next concern was that, I thought this change meant that even on a HDMI-only setup there would be a bitrate-reducing transcode, thus wiping out all the benefits of getting such a new AVR. I didn't want to buy such an AVR to end up with worse audio quality than I get now. But my understanding now is that this isn't the case.
I already understood the point, made earlier in this thread, that there is nothing inherently lower-quality about PCM, compared to passthrough of DTS-HD MA, TrueHD or any other lossless format (except the metadata issue with very new formats, which I'm not going to go into). Whether the decoding of the source happens in Kodi or in the AVR, it should make absolutely no difference to the resulting audio. The digital-to-analogue conversion is still done in the AVR, and that's where their quality can make a difference. (I wonder if some people's reluctance to let go of passthrough is a confusion between the digital-to-analogue conversion and the lossless, digital decode from an encoded bitstream to PCM?)
With this change, my understanding is that the audio from the source is decoded to a waveform which is then resampled to the outgoing PCM stream at the adjusted speed. This is all happening at 24-bit 96KHz, so while that resampling may be very slightly lossy, it really is all happening at a resolution way, way beyond our ability to hear it. Your cat may be able to hear it, but she won't tell, and she probably doesn't like it when you play stuff loud anyway. The lossiness to worry about is during compression to a lossy format such as AC3, and that isn't happening here (unlike with S/PDIF output).
In either case, though, starting from a lossless source probably does make a difference. In the HDMI + Multichannel-PCM scenario, this means that the lossless stream is the basis of the resampling. In the S/PDIF + AC3-transcode scenario, it's still always better to transcode from the best available source. So while, thus far, I've ripped my blu-rays without the lossless formats because I could only pass-through DTS-Core or AC3 to the amp anyway, it may actually now be worth having the lossless tracks there, for Kodi to transcode from.
But again, whether I'd really hear the difference is still questionable!
