Section of Signals from AVR for CD Playing

[timetohunt]

Note: My title is supposed to say Selection of Signals (not section).

Hi there, it been awhile. I just got back into digging a little deeper into the capabilities of
my AVR. I seem to have forgotten a few principles. Here is one that is not explained in the documentation.
(I have read the owners manual cover to cover).

I have a Rotel 1072 CD player connected to my AVR (A Pioneer VSX94-TXH). Like a number of devices, the CD is able to be connected with analog (pair of RCA jacks) and digital (a coax type connector). I have both connected.

So when I have the input set to CD, the signal select button allows the following 4 settings (or at least these are appearing on the display as I scroll through with the button). Outside of possibly some slight change in volume, I am not hearing much of a difference between the four. Could someone possibly explain these and why they are made available. This is the order in which they scroll thru.

1. Digital
2. Auto PCM Digital
3 Auto Digital
For these 3, I am fairly clueless as to the differences. I have my guesses based on what I have read, but its not clear to me.

4. Analog
Unlike a tape or Phono player, I understand that CD is a digital medium, No? So does the setting mean that only the Rotel's DACs are being used?

 

[timetohunt]

Actually, I realized that anything on the display with the word 'Auto' in it, selects the first available signal. This is the default setting and according to the manual the order is HDMI first, DIGITAL second and ANALOG last. The first signal selected on my system with the CD player is AUTO PCM DIGITAL, if you push the button again, the next display is just DIGITAL. I guess I would like to know why PCM DIGITAL is first selection and what that really means in terms of signal processing. If you have a rather high end CD player like mine, do you generally want to use ANALO? Bit confused on that. I know that even with a higher end player that the sound is not going to be much better than a cheaper unit, given the digital source. The only reason I went with the Rotel is because its sturdy and processes HDCDs, of which I own quite a few.

 

[avengineer]

The Pioneer's "Auto PCM" and "Digital", in the case of your signal from your CD player, do the same thing. Your CD player outputs PCM, so that's what is being handled regardless of how the selection is made. Even in terms of how the player is connected, coax or optical, it's still just PCM, and once it's in the AVR, it's all handled identically, which is to be internally up-sampled to 24/96 and processed through the SHARC DSP.

Analog is an interesting situation in this case, if you're actually playing an HDCD. If so, the internal processing of the Rotel is necessary to properly decode the HDCD and get the benefit of that format. The only way that's coming out of the Rotel is the analog jacks. Now that's not a real problem, because your Pioneer AVR will re-digitize that signal at 24/96 (but that performs more like an optimistic 20/96) which should be a fairly good match to the 18 bit HDCD performance (as your Rotel manual states), especially considering HDCD's "Peak Extend" function. But, all that considered, there still be not much to be gained from HDCD > Analog > Pioneer. The reason I say the Pioneer, even though it's spec'd at 24/96 for analog inputs to its ADC, there are no inexpensive real 24/96 ADCs in the world. Most barely make it to 20 bits, with many performing up to 18 bits. A real 24 bit-performance ACD is a beastly expensive device that wouldn't be found in an AVR's rarely-used analog inputs.

So what you've got is an HDCD with an optimistic 18 bits at 44.1 being sent via analog to an ADC running at barely 20/96 performance. The end result will likely be closer to 17/44.1 performance after all of that, and now you're pretty much close to a high-end standard CD player with no HDCD.

Anyway, the short story is, for HDCD playback you should use the analog outputs/inputs. For standard CDs, the coaxial connection (PCM) would be better, slightly.

 

[timetohunt]

The Pioneer's "Auto PCM" and "Digital", in the case of your signal from your CD player, do the same thing. Your CD player outputs PCM, so that's what is being handled regardless of how the selection is made. Even in terms of how the player is connected, coax or optical, it's still just PCM, and once it's in the AVR, it's all handled identically, which is to be internally up-sampled to 24/96 and processed through the SHARC DSP.

Analog is an interesting situation in this case, if you're actually playing an HDCD. If so, the internal processing of the Rotel is necessary to properly decode the HDCD and get the benefit of that format. The only way that's coming out of the Rotel is the analog jacks. Now that's not a real problem, because your Pioneer AVR will re-digitize that signal at 24/96 (but that performs more like an optimistic 20/96) which should be a fairly good match to the 18 bit HDCD performance (as your Rotel manual states), especially considering HDCD's "Peak Extend" function. But, all that considered, there still be not much to be gained from HDCD > Analog > Pioneer. The reason I say the Pioneer, even though it's spec'd at 24/96 for analog inputs to its ADC, there are no inexpensive real 24/96 ADCs in the world. Most barely make it to 20 bits, with many performing up to 18 bits. A real 24 bit-performance ACD is a beastly expensive device that wouldn't be found in an AVR's rarely-used analog inputs.

So what you've got is an HDCD with an optimistic 18 bits at 44.1 being sent via analog to an ADC running at barely 20/96 performance. The end result will likely be closer to 17/44.1 performance after all of that, and now you're pretty much close to a high-end standard CD player with no HDCD.

Anyway, the short story is, for HDCD playback you should use the analog outputs/inputs. For standard CDs, the coaxial connection (PCM) would be better, slightly.

Thank you. This was an interesting read. One item of conflict might be that my HDCD indicator light is lit even if I have Digital selected. In other words, I don't have to select Analog in order for the machine to display HDCD processing. However; I don't know if the light simply tells us that an HDCD has been inserted. I would hope that light would indicate HDCD processing. If so, then I don't know what is actually going on. Also, perhaps my saying that my Rotel 1072 is a high end player may be overstated. I don't know what else is out there, I would think that $750 (my Rotel) is quite a bit for a box that only plays CDs, but I am sure it gets beyond that. Even so, I doubt I could squeeze any additional sound that my beat up ears could hear the difference. I really liked the way you explained the performance in bits/cycles terms. The engineer side of my brain thanks you.

 

[avengineer]

Thank you. This was an interesting read. One item of conflict might be that my HDCD indicator light is lit even if I have Digital selected. In other words, I don't have to select Analog in order for the machine to display HDCD processing. However; I don't know if the light simply tells us that an HDCD has been inserted. I would hope that light would indicate HDCD processing. If so, then I don't know what is actually going on. Also, perhaps my saying that my Rotel 1072 is a high end player may be overstated. I don't know what else is out there, I would think that $750 (my Rotel) is quite a bit for a box that only plays CDs, but I am sure it gets beyond that. Even so, I doubt I could squeeze any additional sound that my beat up ears could hear the difference. I really liked the way you explained the performance in bits/cycles terms. The engineer side of my brain thanks you.

The puzzle here isn't that the HDCD lit is on regardless of what output you use (it's just showing an HDCD is present, and it's processing it), but if the HDCD processing in any way affects the digital output. I think it may not, but that would be something to ask Rotel about. I didn't see it in the manual. You know for sure the HDCD processing is happening on the analog outputs.

Your Pioneer has no idea about HDCD, and the Rotel has no idea which output you are using, so the light only shows that an HDCD disc is loaded. The two devices are not chatting back and forth, they are autonomous.