Theoretical question about 5.1 analog connection - AVS Forum
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post #1 of 33 Old 09-14-2007, 03:15 PM - Thread Starter
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OK folks, here's the question from someone who doesn't exactly understand all the audio stuff. Normally don't start new threads since a lot of good info is already out there, but my situation is somewhat unique.

I do not have an HD-DVD player, but contemplating getting one, and I am curious how my specific situation affects the 5.1 analog vs. optical decision.

I have an older Sony ES receiver (DA555ES) which has optical in and a set of 5.1 analog connections. Now, normally I would imagine that the 5.1 analog connection would always be better than the optical.

However, I do NOT and probably never will have rear speakers -- in fact, I don't even have a center channel right now! Once certain furniture constraints ease, I will add a center channel, but I am currently running a 2.1 setup and will never have more than a 3.1 setup (L/R/C + sub).

So.......

Given the lack of surrounds, what would happen if I, for example, got a used HD-A1 and ran the 5.1 analog connection to my receiver? I have "Rear" as well as "Center" selected as "No" on my receiver, so it knows I'm just running 2.1.

Would my receiver automatically downmix the 5.1 analog input to 2.1?

And, more importantly, will this downmixed 2.1 offer any improvement over simply getting DD 5.1 over optical? What about if I add a center and go 3.1?

And, moreover, will a downmixed 5.1 be WORSE than just getting 2.0 PCM over optical? My receiver does a great job with bass management so when I watch 2.0 material I don't really miss the .1 too much, but should 2.0 PCM theoretically be of superior sound quality than a DD 5.1 mix downmixed by the receiver to 2.1? Isn't DD compressed and PCM lossless?

Thanks for any insights! This audio codec stuff is new to me!

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post #2 of 33 Old 09-14-2007, 03:22 PM - Thread Starter
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And, of course, I recognize that in most cases the correct answer to my question is:

"It depends, you have to try them both and see which one sounds better."

However, I don't have a player yet, and I'm more curious as to what should theoretically be superior on a 2.1 set-up:

2.0 PCM via optical
5.1 DD via optical downmixed by receiver to 2.1
5.1 analog to receiver

Thanks again!

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post #3 of 33 Old 09-14-2007, 03:35 PM
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can you tell the difference between dolby digital and CD audio? if so, then even with a 2.1 setup, dolby digital+ and dolby truehd will still be better than optical. dolby digital+ and truehd is very comparable to cd audio and dvd-audio, respectively. i'm not sure if the Xa1 will allow you to disable the rear channels to downmix them to 2.1. however, you can disable the center. i don't have center speaker myself, i use phantom mode. i bought the xa2 w/ analog outs because i'm tired of listening to crappy dolby digital. results may vary however.

also, the volume control will be the only one that will work in your receiver using analog outs, everything for the most part will be disabled.

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post #4 of 33 Old 09-14-2007, 03:56 PM
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You should be able to turn off all the speakers except for the 2.1 you want.
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post #5 of 33 Old 09-14-2007, 03:58 PM - Thread Starter
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Quote:
Originally Posted by trentR View Post

i'm not sure if the Xa1 will allow you to disable the rear channels to downmix them to 2.1.

But if I connect all 6 RCA's for a 5.1 analog connection, will my RECEIVER correctly downmix the 5.1 analog input to 2.1? And will this downmixed 2.1 actually sound better than just getting 2.0 PCM over optical (or DD 5.1 downmixed).

So (leaving aside analog 5.1 for a sec) am I correct in interpreting you that regular DD (5.1) downmixed to my 2.1 setup will be WORSE in quality than just 2.0 PCM?

I listen to CD's over optical at 2.0 PCM and it sounds great, however it's tough to compare music to movies...

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post #6 of 33 Old 09-14-2007, 04:01 PM - Thread Starter
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Quote:
Originally Posted by moparfan View Post

You should be able to turn off all the speakers except for the 2.1 you want.

Thank you for the response, but I don't think that was really my question -- are you saying turn off the speakers in the HD-DVD player or on the receiver? (If you mean the receiver, the "center" and "rears" are already set to "No").

I guess, simply, my question is which should theoretically provide the highest quality from an HD-DVD to my Sony ES receiver:

1. 5.1 analog connection, with the receiver downmixing to 2.1
2. optical connection, 5.1 DD with receiver downmixing to 2.1
3. optical connection, 2.0 PCM

Or are there other options that I'm missing?

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post #7 of 33 Old 09-14-2007, 04:28 PM
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If you disable the speakers in the HD players audio set up you should get a 2.1 downmix. The receiver wont downmix to 2.1 via 5.1 in.

The sound quality whether you use optical or the analog out on the HD player will be the same, optical may sound louder, but loud doesn't equal quality.

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post #8 of 33 Old 09-14-2007, 04:53 PM
 
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Just use the optical. You can get 2 channel PCM from optical which is this same quality as the audio coming from the analog, plus the receiver can mix the 2.0 PCM into 2.1 or 3.1 very nicely.
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post #9 of 33 Old 09-14-2007, 05:00 PM
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Quote:
Originally Posted by rage2wrath View Post

Just use the optical. You can get 2 channel PCM from optical which is this same quality as the audio coming from the analog, plus the receiver can mix the 2.0 PCM into 2.1 or 3.1 very nicely.

If he uses optical, the best he can get is PCM for CD audio and DD/DTS for movies. However, if he uses analog outs you can get all of the above plus DD+ and TrueHD. TrueHd can potentially sound like DVD-Audio, depending on the bitrate, etc used. So, if he wants the best quality sound for his 2.1 setup, go with analog outs.

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post #10 of 33 Old 09-14-2007, 05:10 PM
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Quote:
Originally Posted by batpig View Post


So (leaving aside analog 5.1 for a sec) am I correct in interpreting you that regular DD (5.1) downmixed to my 2.1 setup will be WORSE in quality than just 2.0 PCM?

assuming the same song, DD 5.1 is worst than PCM 1.0(one speaker) in terms of sound quality. DD is similar to MP3.
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post #11 of 33 Old 09-14-2007, 06:13 PM - Thread Starter
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Quote:
Originally Posted by JDF1384 View Post

If you disable the speakers in the HD players audio set up you should get a 2.1 downmix. The receiver wont downmix to 2.1 via 5.1 in.

So, are you saying that the receiver can't do anything with 5.1 analog inputs? In other words, if I only have L/R + sub, I'll lose all the audio in the center and rear channels?

In other words, if I'm going to use analog outs, and only have a 2.1 setup, I should only run three RCA's (one each for L/R and sub) and turn off the other channels in the HD-DVD player?

So the downmix has to be performed in the player? The receiver won't do it? Is this analogous to the way some receivers can't perform any processing/effects on multichannel PCM?

Thanks so much guys for all the info! Keep it coming!

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post #12 of 33 Old 09-14-2007, 07:11 PM
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For most receivers, 5.1 analog in is a simple pass through. The receiver won't apply any processing or downmix other than volume control. I have no clue how your specific receiver is designed. But you best bet is proper config your player to output 2.1.
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post #13 of 33 Old 09-17-2007, 01:10 PM - Thread Starter
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Bump for the monday-morning work crowd -- anyone else have any thoughts on this? Considering I'd only be running a 2.1 setup, would I get better quality using analog ins to my Sony ES receiver, or just 2.0PCM via optical?

basically, trying to decide if I'd rather find a good deal on a used A1 for the analog connections, or if it won't matter for my non-5.1 situation so I should just get an a20/a30...

Thanks!

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post #14 of 33 Old 09-17-2007, 01:41 PM
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Quote:
Originally Posted by batpig View Post

Bump for the monday-morning work crowd -- anyone else have any thoughts on this? Considering I'd only be running a 2.1 setup, would I get better quality using analog ins to my Sony ES receiver, or just 2.0PCM via optical?

Use linear PCM via optical Toslink or just the two channel analog stereo outputs of the player. Let your receiver do the subwoofer crossover. Absolutely no benefit gained in your case with using the 5.1 analog outputs. Stereo linear PCM would give you the full two channel benefits of DD+ or TrueHD. Make sure the player is set to two channel.
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post #15 of 33 Old 09-17-2007, 02:57 PM - Thread Starter
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Thanks -- so to recap for my own clarification:

1. when I run optical to the receiver and it lights up as "2.0 PCM" that's identical to the sound I'd be getting from just running L/R RCA analog cables?

2. DD is compressed, and therefore of a lower sound quality than PCM -- the reason people use DD is to get the 5.1 channels, not because it sounds better (on a channel per channel basis) than analog PCM connection?

3. The benefit of TrueHD (or other HD audio formats) is uncompressed sound on 5.1 channels, giving you the best of both worlds between 2.0 PCM and 5.1 DD? But because I'm only running two channels anyway, I wouldn't see the benefit?

A simple "Yes, you've got it now" or "No, you're still confused on XXX" would be much appreciated to these three points.

Thanks again for the initiation!

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post #16 of 33 Old 09-17-2007, 02:59 PM - Thread Starter
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Ooh, one more "yes/no" quick answer question:

4. Sending 5.1 DD to my receiver and having it downmix to 2.1 should theoretically be of lower sound quality than just 2.0 PCM via optical (or L/R analog RCA)?

Thanks!

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post #17 of 33 Old 09-20-2007, 06:15 AM
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I would use the player to configure your setup as 2.1 currently (i.e set the center and surrounds to "no"). Then I would come out with four cables, front left, front right, center (for later use) and sub. I'd also hook up the coax or toslink to compare, but decoded TrueHD or uncompressed pcm will always sound better through the analogs than coming in coax/toslink....the bit rate and bandwidth are larger (coax/toslink can only handle up to 2 channel 24/96, assuming your receiver has decent 24/96 dacs). For standard good ol' DD and DTS it wouldn't matter, use coax and tell the receiver about your setup....

My $.02

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post #18 of 33 Old 09-20-2007, 10:49 AM - Thread Starter
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sounds good, thanks -- the da555es definitely has good 24/96 DACs.

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post #19 of 33 Old 09-20-2007, 12:49 PM
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Quote:
Originally Posted by ted_b View Post

I would use the player to configure your setup as 2.1 currently (i.e set the center and surrounds to "no"). Then I would come out with four cables, front left, front right, center (for later use) and sub.

I thought that there were reports that the Toshiba HD DVD players did not correctly re-redirect the center channel sound to the L/R mains when the center was set to OFF in the player's audio setup menu (no good phantom center effect). To be safe I would just set the overall player setting to 2 chan and let the AVR do the subwoofer crossover given just L/R main speakers and a subwoofer (2.1 speakers).
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post #20 of 33 Old 09-20-2007, 12:55 PM
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Quote:
Originally Posted by bobgpsr View Post

I thought that there were reports that the Toshiba HD DVD players did not correctly re-redirect the center channel sound to the L/R mains when the center was set to OFF in the player's audio setup menu (no good phantom center effect). To be safe I would just set the overall player setting to 2 chan and let the AVR do the subwoofer crossover given just L/R main speakers and a subwoofer (2.1 speakers).

Then I'd either do what Bob is saying (which negates any hi-resolution/bandwidth stuff, it's all digital coax or toslink now; the AVR will not do bass management on analog ins)....or....not buy the Toshiba player, cuz that implementation glitch is not worth investing in.

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post #21 of 33 Old 09-20-2007, 01:04 PM
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Originally Posted by ted_b View Post

Then I'd either do what Bob is saying (which negates any hi-resolution/bandwidth stuff, it's all digital coax or toslink now; the AVR will not do bass management on analog ins)....or....not buy the Toshiba player, cuz that implementation glitch is not worth investing in.

You do get the high resolution benefit but for only the two channel input. Using S/PDIF set to PCM gets you a 2 channel lossless digital connection, so you still benefit from DD+ or TrueHD. Since you only have L/R mains and a subwoofer, you get all the advanced audio codec benefit that you can use.
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post #22 of 33 Old 09-20-2007, 01:25 PM
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Quote:
Originally Posted by bobgpsr View Post

You do get the high resolution benefit but for only the two channel input. Using S/PDIF set to PCM gets you a 2 channel lossless digital connection, so you still benefit from DD+ or TrueHD. Since you only have L/R mains and a subwoofer, you get all the advanced audio codec benefit that you can use.

That's good to know. I wasn't aware that it would stay lossless up to the 24/96 spdif threshold. I just assumed it downmixed to DD. Good option then.

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post #23 of 33 Old 09-20-2007, 01:49 PM
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Quote:
Originally Posted by batpig View Post

Thanks -- so to recap for my own clarification:

2. DD is compressed, and therefore of a lower sound quality than PCM -- the reason people use DD is to get the 5.1 channels, not because it sounds better (on a channel per channel basis) than analog PCM connection?

3. The benefit of TrueHD (or other HD audio formats) is uncompressed sound on 5.1 channels, giving you the best of both worlds between 2.0 PCM and 5.1 DD? But because I'm only running two channels anyway, I wouldn't see the benefit?

No. You are confusing the term compression with data loss - they are not the same thing.

All codecs use a 'compressed' datastream. However, there is no 'compression' of the audio. The use of the term 'compression' in referring to the audio output from a digital system is incorrect and can cause lots of confusion. It is much more clear to use the descriptive terms 'lossy' and 'lossless'.

PCM (as used on HD media for audio encoding) is not a codec, per se - it represents the pure data stream. This sometimes referred to as 'LPCM' which is redundant, but descriptive.

A lossy codec is one where the output signal is not exactly the same as the input signal, i.e., some data was 'lost'. Most lossy codecs currently in use work with 'perceptual encoding'. This means that they attempt to make the output audio as close to the input as possible, but in terms of what the human ear can perceive (not just what the math says). With a lossy codec, increasing the available digital bandwidth will generally reduce the amount of loss, and get you closer to the original signal. The resulting change/loss is NOT compression, as there will not necessarily be any change in the ultimate dynamic range. DD is a lossy codec; DD+ is also lossy, but it uses a higher bandwidth so that it's performance is far better than 640k DD. Thus, DD will not sound as good as (L)PCM, but not because of compression - it's because it's lossy.

A lossless codec is one where the output signal will be mathematically identical to the input signal. Think of this as the equivalent to a .ZIP file on your computer; whatever you put in comes out exactly the same - it just takes up less space. Thus, the output of a mathematically lossless codec is indistinguishable from the original source (assuming equal rate and bit depth) and/or (L)PCM. TrueHD and dts-MA are lossless codecs, but the datastream is still compressed.
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post #24 of 33 Old 09-20-2007, 01:52 PM
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Quote:
Originally Posted by bobgpsr View Post

I thought that there were reports that the Toshiba HD DVD players did not correctly re-redirect the center channel sound to the L/R mains when the center was set to OFF in the player's audio setup menu (no good phantom center effect).

IIRC, the center channel was being redirected to L/R mains, but it was still present on the center output. I can check this evening to see for sure....
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post #25 of 33 Old 09-20-2007, 02:27 PM
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Quote:
Originally Posted by MauneyM View Post

IIRC, the center channel was being redirected to L/R mains, but it was still present on the center output. I can check this evening to see for sure....

So if that is true then the OP with his 2.1 speaker setup would get the benefit of a discrete sub/LFE channel if he used the 5.1 analog connection. Also all the fun of getting the sub calibrated correctly.
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post #26 of 33 Old 10-04-2007, 04:04 PM - Thread Starter
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Quote:
Originally Posted by MauneyM View Post

No. You are confusing the term compression with data loss - they are not the same thing.

All codecs use a 'compressed' datastream. However, there is no 'compression' of the audio. The use of the term 'compression' in referring to the audio output from a digital system is incorrect and can cause lots of confusion. It is much more clear to use the descriptive terms 'lossy' and 'lossless'.

PCM (as used on HD media for audio encoding) is not a codec, per se - it represents the pure data stream. This sometimes referred to as 'LPCM' which is redundant, but descriptive.

A lossy codec is one where the output signal is not exactly the same as the input signal, i.e., some data was 'lost'. Most lossy codecs currently in use work with 'perceptual encoding'. This means that they attempt to make the output audio as close to the input as possible, but in terms of what the human ear can perceive (not just what the math says). With a lossy codec, increasing the available digital bandwidth will generally reduce the amount of loss, and get you closer to the original signal. The resulting change/loss is NOT compression, as there will not necessarily be any change in the ultimate dynamic range. DD is a lossy codec; DD+ is also lossy, but it uses a higher bandwidth so that it's performance is far better than 640k DD. Thus, DD will not sound as good as (L)PCM, but not because of compression - it's because it's lossy.

A lossless codec is one where the output signal will be mathematically identical to the input signal. Think of this as the equivalent to a .ZIP file on your computer; whatever you put in comes out exactly the same - it just takes up less space. Thus, the output of a mathematically lossless codec is indistinguishable from the original source (assuming equal rate and bit depth) and/or (L)PCM. TrueHD and dts-MA are lossless codecs, but the datastream is still compressed.

Just noticed that a few more posts appeared on this thread -- thanks so much for the input, that makes a lot more sense now and I see the potential for confusion between "lossless/lossy" and "compression" in the sense that I used it.

So, if you don't mind humoring me and answering a couple of quick yes/no questions as I try to make sure I really understand the situation:

(Yes/No) 1. A 2.0 PCM signal over toslink is identical in sound quality to running two L/R analog RCA cables (because both are identical lossless streams) and the only difference would be whether I want to use the player's DAC's or the receiver's DAC's

(Yes/No) 2. Assuming I am correct that the answer to Q1 is "yes", this 2-channel PCM signal should theoretically be of higher quality than sending 5.1 DD to my receiver and having it downmix to 2.1 (because DD is a lossy format and the PCM isn't)

(Yes/No) 3. Because I am running a 2.1 set-up, the 2.0 PCM signal (whether via optical or L/R RCA from the analog stereo outs) will theoretically sound JUST AS GOOD as Dolby TrueHD via analog outs (3 cables, one each for L/R and 0.1 channel)? (because the 2.0 PCM signal is lossless, just like the Dolby TrueHD)

(Yes/No) 4. The only difference I would get from running the analog outs would be the separation of an LFE channel, and that my receiver wouldn't be able to do any processing on the audio.

(Yes/No) 5. Considering all this, with my 2.1 setup, there isn't much reason to get an A1 over an A2 because I wouldn't see the benefit of the analog outs. I would get equivalent sound quality sending 2.0 PCM over optical or RCA L/R and letting my Sony ES receiver take case of bass management.

Thanks so much for the feedback!!!

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post #27 of 33 Old 10-05-2007, 10:30 AM - Thread Starter
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bump for the morning crowd -- simple yes/no answers to these questions would be much appreciated! thanks!

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post #28 of 33 Old 10-05-2007, 10:49 AM
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Which HD DVD player are you looking to get? Which one has the Analog outs?

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post #29 of 33 Old 10-05-2007, 11:06 AM - Thread Starter
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the thread originated as I contemplate whether a used A1 or an A2/3 would better suit my needs -- basically, in a nutshell, would I see any benefit from the analog outs vs. optical when I'm using a 2.1 set-up?

People gave me some great feedback, I think I understand the issues better now -- at this point I just want someone who really understands this stuff to sign off "yes" for me on my 5 questions in post #26 so I can feel reassured that I have an accurate grasp of the situation.

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post #30 of 33 Old 10-05-2007, 04:47 PM
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Quote:
Originally Posted by batpig View Post

(Yes/No) 1. A 2.0 PCM signal over toslink is identical in sound quality to running two L/R analog RCA cables (because both are identical lossless streams) and the only difference would be whether I want to use the player's DAC's or the receiver's DAC's

Assuming that the data rates are correct and supported, yes.

Quote:


(Yes/No) 2. Assuming I am correct that the answer to Q1 is "yes", this 2-channel PCM signal should theoretically be of higher quality than sending 5.1 DD to my receiver and having it downmix to 2.1 (because DD is a lossy format and the PCM isn't)

Yes - toslink doesn't have the bandwidth to handle lossless 5.1.

Quote:


(Yes/No) 3. Because I am running a 2.1 set-up, the 2.0 PCM signal (whether via optical or L/R RCA from the analog stereo outs) will theoretically sound JUST AS GOOD as Dolby TrueHD via analog outs (3 cables, one each for L/R and 0.1 channel)? (because the 2.0 PCM signal is lossless, just like the Dolby TrueHD)

I believe that this would be dependent on how it was mastered. I'm a bit fuzzy on how the LFE data is encoded into the 2.0 PCM stream, as opposed to the 5.1. I think that you would probably lose resolution on the LFE signal, because of the 10 dB offset. In short, the LFE channel must be level-shifted by 10 dB prior to mixing with the main audio, so you necessarily will get some amoun of quantization error.

Quote:


(Yes/No) 4. The only difference I would get from running the analog outs would be the separation of an LFE channel, and that my receiver wouldn't be able to do any processing on the audio.

See above re: LFE.

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(Yes/No) 5. Considering all this, with my 2.1 setup, there isn't much reason to get an A1 over an A2 because I wouldn't see the benefit of the analog outs. I would get equivalent sound quality sending 2.0 PCM over optical or RCA L/R and letting my Sony ES receiver take case of bass management.

That depends on how good a system you have, and how much you care about the accuracy of the LFE signal.
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