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Discussion Starter · #1 ·
Hello all,


If you know of a good post that answers my question, feel free to link me. I didn't find one.


My question boils down to: "What kind of signal can be passed through a digital coaxial port?"


Background: I have a Yamaha RX-V3300. I plan on purchasing a Blu-Ray player. I could of course purchase a high-quality unit with 5.1 analog outputs to use with my receiver, but I would prefer to have the 3300 do the digital to analogue conversion (under the assumption that Yamaha receivers do a good job of this.) But, if I were to connect a blu-ray player via the digital coaxial port and have it re-encode the digital source from TrueHD/DTS Master Audio into a PCM signal, what kind of quality would I get from that?


Specifically, what frequency and bitrate can a blu-ray player output a PCM signal? I'm pretty sure the Yamaha says "192khz/24bit DAC" on it, so I assume it can handle anything the player would throw at it. Would the player give it PCM signal that matches lossless TrueHD source, or is the quality lowered when output over digital coax (or optical.)


If it's lowered . . . what would sound better? Trusting a blu-ray player's DAC's to give me good output from the lossless source, or letting the Yamaha do the heavy lifting on a diminished digital signal?


I'm very interested to know the specifics if anyone knows exactly what the frequency and bitrate of the output are. Also, I've noticed many Disney DVD's state "uncompressed 48khz/24bit audio." Is this just a PCM file? Would that be output directly via the digital coax, or decreased to a more-CD quality file?
 

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I can offer a little help, I think.


S/PDIF whether optical or coax is limited to three main audio types -


* Two channel PCM

* DTS

* Dolby Digital


PCM places no inherent limit on PCM bit rate. I assume receivers have varied a bit in what they can handle. Bit depth is limited to 20 or 24 bits, I forget which.


Blu-ray discs would usually provide either a high quality Dolby Digital track or a core DTS track for compatibility. I think they are good enough that you should not worry about it.


The Dolby Digital track will be 640 kbs, which is signficantly better than the low rate 300 something kbs often found on DVDs.


The DTS track is 1.5 Mbs, which is twice what is commonly found on DVD discs.


There is no conversion needed, by the way. The DTS track on the Blu-ray disc contains a core DTS track even when it's lossless. Discs with a TrueHD track should have a companion DD track which will play over optical/coax.
 

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Discussion Starter · #3 ·
Okay, thank you for that answer.


To recap: I would be able to get a signal at the uppermost quality limit for either Dolby Digital (the codec used on DVDs, but at 640kbps a higher bitrate than that used with DVD's) or DTS (the other codec used on DVDs at a higher bitrate, 1.5mbps, than DVDs). A Blu-Ray player CANNOT uncompress a TrueHD / Master Audio signal and send the full-quality signal via S/PDIF (only over HDMI, I assume).


Do I have that right?


So, if I want the lossless audio, I should aim for a player with analog outputs then?
 

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Right. S/PDIF can't handle lossless audio for more than two channels, because the only way to do more than two channels over S/PDIF is a DD or DTS, which are lossy.


And yep, you could invest in a player with MC analog outputs.


You want my advice, for what it's worth, just use DD/DTS. If you look at the stickied AVR FAQ, there's a section on lossless audio. It includes a link to an article about a listening test. The listening test asserts that lossy Blu-ray audio is excellent.


Unless you watch a lot of concerts, why the need for the very best sound when the difference is arguably only slight with lossless. For dialog and loud bangs, and background music, I would not personally worry about the subtle differences I have heard with lossy encoders.


Let me give another example - MP3 files. 128 kbs MP3 is not as good as 256 kbs MP3. But I never heard other than subtle differences. 128 kbs is 64 kbs / channel. 256 kbs MP3, which I can't personally tell apart from lossless is 128 kbs / ch.


Consider 640 kbs DD. I don't know how DD and MP3 file quality compares at a same bitrate. I guess that the quality of 640 kbs is between 128 kbs MP3 and 256 kbs MP3 though. Not bad at all IMO, and the listening test seems to back me up - I encourage you to read it, in case it simplifies your life.


MC Analog does complicate things such as bass management as well.
 
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