2015-10-17, 13:27
(2015-10-17, 04:21)wrxtasy Wrote: From what I've gathered:
Quote:Audio Output > AMLogic-HDMI/SPDIF with:Lossy 5.1 Audio is Lossless Audio (HD Passthrough) that is compressed, basically filtering out the audio frequencies that are beyond a Human Ears Hearing range. Your dog might like lossless Audio !
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Passthrough Enabled:
DTS HD MA/HRA > lossy 5.1 DTS (or 6.1 DTS-ES)
Dolby True HD > lossy 5.1 Dolby Digital
Not quite. The DTS-HD MA/HRA standard used for Blu-ray (and HD-DVD - remember that) is based on a two-tier encode. The audio is made up from two streams, a DTS core stream, which is what will be output over SPDIF on Blu-ray players, and will be output as passthrough on non-DTS-HD friendly players (*). There is then a secondary "helper" stream which contains a compressed "difference between lossy and lossless" signal which along with the DTS core stream allows a lossless stream to be created.
Dolby True HD works differently I believe. There are two separate and independent audio streams. The Dolby True HD stream - which is entirely standalone, and a 'hidden' lossy Dolby stream. There isn't a core per se.
The lossy compression level is decided by those mastering the discs.
However this bit : basically filtering out the audio frequencies that are beyond a Human Ears Hearing range. Your dog might like lossless Audio is definitely a misconception. It isn't HF content that is filtered out for lossy compression, it's a lot more complex than that.
Lossy compression - like MP3, AAC, Dolby Digital, DTS etc. use techniques like psycho-acoustic modelling, that take advantage of the way the ear and brain interact. Things like a quiet sound at one frequency being masked by a loud sound at a different frequency. (You might be able to hear one person whispering quietly in a room on their own, but if someone else then starts shouting the whisper will disappear to you) If most people can't register the quiet sound, then don't waste data sending it. However the processing involved to do this compression can have quite an effect on subtle aspects of the audio like phase coherence (which is important for stereo imaging if content has been captured with cross-pair or similar stereo mics rather than just being panned mono sources across a sound field) If you hear over compression on Dolby (I have a poorly mastered 5.1 disc that sounds like AM radio...) you can definitely hear it. Broadcast AC3 is often at low bitrates like 348k - and you can definitely hear artefacts without being a dog...
Some compression for stereo will also take advantage of the similarities between left and right channels - which can deliver good bit rate reductions but can also hammer some aspects of the audio. (For instance killing Dolby analogue surround that would be decoded via ProLogic)
Quote:Now the debate is would you be able to tell the difference between Lossless and Lossy Audio anyway in a blindfolded controlled test ?
Yes - and I suspect high bitrate Dolby (640k or higher) / DTS (1.5Mbs) is very difficult to hear the difference from HD Audio. I'm not sure I can in every situation - but on the other hand, why listen to a compressed version if you can listen to the original.
Quote:You will also need pretty decent speakers to even hear the full audio frequency range contained in Lossless Audio, otherwise you are just admiring those loverly bling blinken DTS HD and True HD lights on your AVR. I suspect thats what a lot of people want anyway, and the Audio Marketers know this and ramp up the HD Audio Hype.
I think you are confusing high-sampling rate (96/192kHz) and HD Audio. You can have lossy compressed 96/192kHz tracks. And most HD Audio tracks are 48kHz sampling, as most DD/DTS is, so it isn't a case of capturing higher frequencies, it is a case of not altering the recorded sound.
In most cases the frequency range of DD/DTS and DTS-HD/True HD are the same...
(*) Assuming you aren't transcoding to Dolby OR outputting PCM 2.0 decoded.