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post #1 of 53 Old 07-11-2009, 07:11 AM - Thread Starter
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Stumbled into this article on Engadget. Thought some of you might find it interesting.


LPCM is not always equal to bitstream
by Ben Drawbaugh, posted Jul 11th 2009 at 8:38AM

This is an on going debate on certain forums and for good reason. The fundamental question is where should you decode your lossless audio? In DVD players we almost always decoded compressed audio in the A/V receiver, but when it comes to Blu-ray features like Bonus View, there is at least one specific reason to decode in the player.


It really come down to your system. If you have a great A/V receiver and a great decoder in your player, than it shouldn't make a difference where you decode. But saying that LPCM is always equal to bitstream just isn't correct. Sure, the decoder must be able to decode perfectly to be certified and get the sticker on the box, but that doesn't mean the player's analog circuitry or HDMI chip doesn't screw it up after the fact. It also doesn't mean that your A/V receiver treats LPCM audio the same as it does audio that is internally decoded. Some think its silly to find satisfaction in seeing that little logo on your A/V receiver light up when it receives DTS-HD, but there is some comfort to knowing that the signal at least made it to your A/V receiver before getting mucked up. And lets face it, if your A/V receiver can't be trusted to properly handle the audio, does it really matter what signal it received?

The long and the short of it is that "it depends," meaning it comes down to your equipment and your preferences. We think it's a good idea to choose equipment that offers multiple options so you can discover the best combination yourself. Although we do admit that 90 percent of even the most elite HD snobs can't distinguish a difference, but since when have we let that stop us from obsessing over the ultimate setup?


Link to article....

HERE

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post #2 of 53 Old 07-11-2009, 07:19 AM
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imo, that article is akin to "teach the controversy" logic... with a healthy dose of "audiophile shamanism" thrown in...

it's littered with "maybe", "could" and "might"... no hard data whatsoever...

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post #3 of 53 Old 07-11-2009, 07:25 AM
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That's about the only thing Ben from Engadget good at: stir up controversy to attract traffic to the website.
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post #4 of 53 Old 07-11-2009, 07:30 AM
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The analog circuitry in the player isn't involved in decoding so it can't "screw it up after the fact". And if the HDMI chip can't deliver the PCM correctly, I wouldn't have much confidence that it can deliver the bitstream correctly either.
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post #5 of 53 Old 07-11-2009, 07:47 AM
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What a pile of crap article.. My 14 year old daughter could have made a more informative discussion. I don't even know what he was trying to say?


... I left a comment on the site.

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post #6 of 53 Old 07-11-2009, 08:07 AM
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I believe the article, while not very useful at all, was actually right.

It DOES depend on your equipment where the decoding is done - thats my understanding and practical experience of HD digital audio.

For the avoidance of doubt, I'm NOT referring to the integrity of the decoding - the ability for either of the player or processor decoders to get the decoding right.

There are some very good reasons for this, but I can feel some faimiliar arguements coming up.....

BR, Nick
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post #7 of 53 Old 07-11-2009, 08:10 AM - Thread Starter
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Quote:
Originally Posted by kplex View Post

The analog circuitry in the player isn't involved in decoding so it can't "screw it up after the fact". And if the HDMI chip can't deliver the PCM correctly, I wouldn't have much confidence that it can deliver the bitstream correctly either.

True only if you output via HDMI from the player. If you're using multichannel analog out, the analog circuitry is a factor to consider.

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post #8 of 53 Old 07-11-2009, 08:10 AM
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I read it and saw no purpose.. There was no take home point for the average reader - except that LPCM is different than bitstreaming... something we all know.

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post #9 of 53 Old 07-11-2009, 08:15 AM - Thread Starter
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Quote:
Originally Posted by thebland View Post

... I left a comment on the site.

Just read it.. Nice one. Should stir it up a bit. I'm curious if the author will reply to that comment.

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post #10 of 53 Old 07-11-2009, 09:06 AM
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Quote:
Originally Posted by thebland View Post

What a pile of crap article.. My 14 year old daughter could have made a more informative discussion. I don't even know what he was trying to say?


... I left a comment on the site.

I love your comment....."the article is word salad"

I'm in agreement with most others....there's really nothing of substantive value in the article.

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post #11 of 53 Old 07-11-2009, 09:22 AM
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When someone discusses analog circuitry when talking about a purely digital signal path, I have to question their knowledge.

Why would an HDMI chip mess up audio?

Remember, her's not talking about the quality of DACs or anything else here. He's talking about where the audio is decoded.

He cites studies from any expert source. He gives no real world example. No listening tests.

I find his conclusions to have no backing.

"But this one goes up to 11"
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post #12 of 53 Old 07-11-2009, 10:52 AM
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Sure, the article wasn't of much value, but a supposedly more enlightened and better informed AVS discussion ought to have more than rhetoric. There's a general asumption that all things digital are perfect, yet players and processors are complicated. They do things differently, and do things wrong, depending on how they are implemented and configured.

1) Some players decode DTS MA bitstream to the core track for LPCM output.

2) Some processors don't decode HD bitstream when they're running room EQ.

3) Some players fall back to DTS when "decoding" dual channel DTS MA.

4) Some players down-sample 24-bit audio to 16-bit when bass management is applied.

5) Some processors use a different audio clock recovery process with bitstream.

6) Some processors lose resolution through truncating and rounding errors.

The sins of analogue audio are readily apparent, but digital audio can do lots of things wrong as well. The best system level performance will be realised when the weak links in the chain are avoided. That sounds like stating the obvious, but I think the article could have gone a bit further.

Nick
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post #13 of 53 Old 07-11-2009, 11:45 AM
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Quote:
Originally Posted by welwynnick View Post

1) Some players decode DTS MA bitstream to the core track for LPCM output.

You should have known your player before buy it (e.g. can it decode DTS-HD MA). It has nothing to do with LPCM vs bitstream argument.

Quote:



3) Some players fall back to DTS when "decoding" dual channel DTS MA.

You can't even bitstream two DTS MA streams over to receiver. I'm not sure how this is related to the argument.

Quote:


4) Some players down-sample 24-bit audio to 16-bit when bass management is applied.

I'm not aware ANY players out there apply bass management when output LPCM via HDMI.

Quote:


6) Some processors lose resolution through truncating and rounding errors.

Such processors will lose resolution regardless with LPCM or bitstream.
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post #14 of 53 Old 07-11-2009, 01:51 PM
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well I still don't buy it that decoding a even an old-school D.Digital/DTS signal is as easy as un-zipping a file - and will always end up with the same result - same as I don't buy it for HD material - I've tested this on 2 separate amps

Yamaha RX-V3800 connected to a PS3

D.Digital DVD

first test: LPCM from PS3 via HDMI (with all Dynamic Compression OFF)
second test: Optical bitstream

Second one sounded a lot more dynamic - just sounded better - they both should sound the same ?

2nd test on new amp - via HTPC

Bluray disk - with PCM lossless

D.Digital 640kbps via Optical digital
Lossless via USB (8 channel)

and again - bizarely the bitstreamed D.Digital sounded more engaging and more dynamic. The USB input has the same postprocessing applied - ie full EQ, speaker distances etc - so no difference there

why I don't know !

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post #15 of 53 Old 07-11-2009, 02:59 PM
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Quote:
Originally Posted by markabuckley View Post

well I still don't buy it that decoding a even an old-school D.Digital/DTS signal is as easy as un-zipping a file - and will always end up with the same result - same as I don't buy it for HD material - I've tested this on 2 separate amps

Yamaha RX-V3800 connected to a PS3

D.Digital DVD

first test: LPCM from PS3 via HDMI (with all Dynamic Compression OFF)
second test: Optical bitstream

Second one sounded a lot more dynamic - just sounded better - they both should sound the same ?

Is it possible dialnorm was applied in one case, and not the other?

Is it possible Dolby Digital compression level was different between the two scenarios?

I guess I can sort of agree it's a bit different than unzipping a file due to the factors of Dialnorm and compression level.

Obviously, both devices need to be applying exactly the same dialnorm and DRC processing or the results would not be the same.

One other thing I thought of. MPCM may have different gain than bitstream for various reasons. Did you measure SPL and make sure it was the same?

People have brought up some good points. The end result could be different for factors not directly related to the decoding process.

"But this one goes up to 11"
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post #16 of 53 Old 07-11-2009, 03:10 PM
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Quote:
Originally Posted by MichaelJHuman View Post

Is it possible dialnorm was applied in one case, and not the other?

Is it possible Dolby Digital compression level was different between the two scenarios?

I guess I can sort of agree it's a bit different than unzipping a file due to the factors of Dialnorm and compression level.

Obviously, both devices need to be applying exactly the same dialnorm and DRC processing or the results would not be the same.

One other thing I thought of. MPCM may have different gain than bitstream for various reasons. Did you measure SPL and make sure it was the same?

People have brought up some good points. The end result could be different for factors not directly related to the decoding process.


not sure to be honest - but I'm pretty sure it wasn't a Dialnorm thing - and compression was definately off in all cases

wasn't volume related either I'm sure

in fact the PS3 decoding the D.Digital off a DVD was very poor (for me anyway) and outputting LPCM ... in fact on TitanAE (if you know the scene where they take a joy ride through the nebulae) - the PS3 seem to decode it very wrong - I don't know how to describe it but almost clipped - not clipped as in the SQ was poor - but that some levelling seem to be occuring (yes all Dynamic Range was off) - played it to a friend of mine and he thought it sounded awful.. We switched back to optical and it sounded fine. I was careful to ensure the Yamah was in the same mode for both optical and LPCM.

if D.Digital/DTS decoding is the same in all cases - then why do some processors and AV amps -with the same features as lower models in the range - sometimes use far more powerful DSP chips ?

Mark.
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post #17 of 53 Old 07-11-2009, 03:20 PM
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Quote:
Originally Posted by markabuckley View Post

if D.Digital/DTS decoding is the same in all cases - then why do some processors and AV amps -with the same features as lower models in the range - sometimes use far more powerful DSP chips ?

Mark.

If that's all separates high end models and lower end models, yeah, who would pay for the extras?

There is really no need for powerful DSP chips for D.D decoding. The powerful DSPs on higher end modals are there for all the additional processings that offered only on high end modals, e.g. THX, DPL IIx, Room EQ etc. that are not found in lower end modals or even if there are some found in lower end modals, you can have like both DTS-HD decoding and Room EQ.

As for comparing decoded LPCM vs bitstream differences are often easily explained by two things:
1. The receiver didn't properly handle LPCM LFE levels (this is the case on many early HDMI 1.1 receivers that require a firmware update)
2. The bitstreamed audio often played at a higher vol level than LPCM. If you level match both, most ppl can't tell any difference.
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post #18 of 53 Old 07-11-2009, 05:12 PM
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Quote:
Originally Posted by Foxbat121 View Post

You should have known your player before buy it (e.g. can it decode DTS-HD MA). It has nothing to do with LPCM vs bitstream argument.
You can't even bitstream two DTS MA streams over to receiver. I'm not sure how this is related to the argument.
I'm not aware ANY players out there apply bass management when output LPCM via HDMI.
Such processors will lose resolution regardless with LPCM or bitstream.

The thread seemed to be growing bits-is-bits blinkers and assuming that all digital signal processing is perfect. I wanted to give some examples of how digital is not perfect, even in the areas where bit integrity is not necessarily an issue. I disagree with some of your comments, but I think we should concentrate on the things that do affect where decoding should be performed.
Quote:
Yamaha RX-V3800 connected to a PS3
D.Digital DVD
first test: LPCM from PS3 via HDMI (with all Dynamic Compression OFF)
second test: Optical bitstream
Second one sounded a lot more dynamic - just sounded better - they both should sound the same ?

This is a case in point. I never bought a PS3 (I wish I had, in hindsight) but I did think it offered a good way to test the bitstream hypothesis without adding other complications or variables. I've been trying for a year to persuade PS3 owners to compare LPCM and bitstream output from DVD DD & DTS soundtracks. And this is the first account I've read where someone has done this. I had supposed that the bitstream output would sound better than the LPCM output for the reasons sort-of-outlined by thebland in the Engadget comments. As long as the comparisons were done an equivalant basis, this suggests that bitstream decoding in the amp is better with SD audio, and I think there is a similar situation with the HD codecs (just with greater SQ potential).
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post #19 of 53 Old 07-11-2009, 06:02 PM
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Quote:
Originally Posted by welwynnick View Post

The thread seemed to be growing bits-is-bits blinkers and assuming that all digital signal processing is perfect. I wanted to give some examples of how digital is not perfect, even in the areas where bit integrity is not necessarily an issue. I disagree with some of your comments, but I think we should concentrate on the things that do affect where decoding should be performed.

Your points listed above are pointless to this debate because you have to compare LPCM vs bitstream when everthing else is the same. There is no point compare receiver A's output to receiver B's output.

Quote:
This is a case in point. I never bought a PS3 (I wish I had, in hindsight) but I did think it offered a good way to test the bitstream hypothesis without adding other complications or variables. I've been trying for a year to persuade PS3 owners to compare LPCM and bitstream output from DVD DD & DTS soundtracks. And this is the first account I've read where someone has done this. I had supposed that the bitstream output would sound better than the LPCM output for the reasons sort-of-outlined by thebland in the Engadget comments. As long as the comparisons were done an equivalant basis, this suggests that bitstream decoding in the amp is better with SD audio, and I think there is a similar situation with the HD codecs (just with greater SQ potential).

Then, you really need to read more. This types of claims have been posted million times here but when asked to (1) level match (2) perform true blind test again, no one ever came back to repeat the claim.
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post #20 of 53 Old 07-11-2009, 06:34 PM
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Movie : Death Race (I ran a specific segment of scene 1)
Receiver : Yamaha RX-V3900 (DD compression set to max range)
Audio Type : Dolby Digital
Transport Method : MPCM over HDMI
Volume : -15 Db
SPL Meter : RS Digital (C, slow)
Peak SPL : 83 dB

Changed PS3 to output DD bitstream. BD/DVD DRC=off (hopefully similar to max on my receiver!)

Peak SPL : 87 dB

So DD does seem like it could be louder. As for why, I could not say. Some difference in processing. I don't think that implies either is better. If we level matched them, they might sound identical.

I certainly encourage others to try this themselves.

"But this one goes up to 11"
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post #21 of 53 Old 07-12-2009, 04:30 AM
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Quote:
Originally Posted by Foxbat121 View Post

Then, you really need to read more. This types of claims have been posted million times here but when asked to (1) level match (2) perform true blind test again, no one ever came back to repeat the claim.

I think my wife would say that I need to read less; on the net at any rate.

As it happens, I HAVE done the sort of tests you describe, and found that there is a difference between LPCM and bitstreaming.

My point is that it's not necessarily down to shortcomings in the bitstream to LPCM decoding process, though there may be faults there as well.

Nick
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post #22 of 53 Old 07-12-2009, 07:17 AM
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So, what you're saying is that your receiver is faulty that can't properly handle the LPCM because many PS3 owners have proved LPCM and bitstream are identical on their system.
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post #23 of 53 Old 07-12-2009, 07:22 AM
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Quote:
Originally Posted by welwynnick View Post

I think my wife would say that I need to read less; on the net at any rate.

As it happens, I HAVE done the sort of tests you describe, and found that there is a difference between LPCM and bitstreaming.

My point is that it's not necessarily down to shortcomings in the bitstream to LPCM decoding process, though there may be faults there as well.

Nick

The differences are typically volume level related. If there were 'jitter' related differences, you'd be hard pressed to reliably find them in movie soundtracks. Moreover, if you had to listen to either LPCM or bitstreaming in your system without the ability to compare them side by side, you'd likely never know of a differences as any differences would be so nuanced..

This is an overblown controversy. 99.9% of AVS folks lack the systems that could possibly identify differences... you'd need a good set of headphones and an audiophile grade recording of few instruments where you could hear decay of some instruments after a note is played, chord struck, etc..

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post #24 of 53 Old 07-12-2009, 08:07 AM
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Quote:
Originally Posted by Foxbat121 View Post

So, what you're saying is that your receiver is faulty that can't properly handle the LPCM

I used a Pioneer SC-07 and a Onkyo SC886, and compared DTHD & DTS MA soundtracks played via LPCM & bitstream from a variety of blu-ray players. I found that bitstream always sounded better, though the difference was most apparent with the Onkyo and with the poorer sounding players. I don't think there's a fault as such, just that some players and processors handle LPCM better than others. I presume this is down to jitter performance. I expect that some receivers and processors will show no benefit with bitstream for various reasons, though I'm not aware of any yet (Classe?).
Quote:
Originally Posted by thebland View Post

The differences are typically volume level related. If there were 'jitter' related differences, you'd be hard pressed to reliably find them in movie soundtracks. Moreover, if you had to listen to either LPCM or bitstreaming in your system without the ability to compare them side by side, you'd likely never know of a differences as any differences would be so nuanced..

Volume - yes. I found that the Onkyo in particular gave about 3dB higher output from bitstream sources than LPCM. Perhaps this is an intentional marketing feature to make bitstreaming sound better, which I think is plain bad, but it was straightforward to compensate for. There are lots of other pitfalls to a fair comparison which are particular to individual equipment, such as bass level, dialnorm and DRC, but I did take them out of the equation, as I did want a genuine result.

Initially I did think bitstreaming made no difference, and I said as much in AVF in Feb/Mar; its a matter of record. However, I was mistakenly using a BD with LPCM soundtrack, thinking it was DTHD. When I switched to real bitstreaming, the difference was quite clear with a cheap BD player. The fact that I achieved a genuine null result (when I was looking for a positive one) gives me some confidence that the real result was valid. I did extensive blind testing with other people and found the same thing.

I have to say though, when using a Denon 3800, the loss with LPCM was rather smaller, and I'd expect a similar situation with other good players like the S5000 and BDP-09. The differences I found were all observed with BD films soundtracks, and were indeed subtle, rather than dramatic. Perhaps there would be no noticeable difference with many blockbuster soundtracks, but explosions aren't really my thing, and the benefits of bitstream are definitely worthwhile with the more subtle stuff, of which there's plenty. I KNOW a lot of people don't agree with this, but its all IMHO of course, yet easy enough to demonstrate.

Nick
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post #25 of 53 Old 07-12-2009, 09:45 AM
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I second that assessment in regards to LPCM not being equal to Bitstream. I realized that yesterday when I hooked up my new Panasonic DMP-BD60 to my Integra DTC9.8 Pre Pro, previously I had my PS3 connected to the Integra DTC 9.8 "which the PS3 was only able to play LPCM for high resolution audio" the PS3 did the high resolution audio up-converting internally then it was send to the receiver as source material, the sound was great not saying it was bad, but now that I have the receiver do the high resolution up-converting the sound is just so much better with high resolution audio via BD-Discs, and the receivers front panel tells you what high resolution audio is playing like Dolby True HD, with the PS3 doing the up-converting of High Res audio the receivers front panel would show Multichannel.

When initially installing the Panasonc Blu-Ray player I let the Panasonic do the High resolution audio up-converting, it did the same job as the PS3, which was great but not as detailed as the Integras high resolution up-converting via true bit streaming instead of LPCM.
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post #26 of 53 Old 07-12-2009, 11:16 AM
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Originally Posted by cybertec View Post

.....and the receivers front panel tells you what high resolution audio is playing like Dolby True HD, with the PS3 doing the up-converting of High Res audio the receivers front panel would show Multichannel....

i'm sure you didn't "mean to", but imo, you just pointed out the biggest reason why people "hear" a difference....

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post #27 of 53 Old 07-12-2009, 11:23 AM
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Quote:
Originally Posted by ccotenj View Post

i'm sure you didn't "mean to", but imo, you just pointed out the biggest reason why people "hear" a difference....

well my receiver just displays "USB" - and I still hear a difference !
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post #28 of 53 Old 07-12-2009, 12:13 PM
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I don't think you can say bitstream sounds better until you account for a potential volume difference between bitstream and PCM.

"But this one goes up to 11"
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post #29 of 53 Old 07-12-2009, 01:19 PM
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I don't think you can say bitstream sounds better until you account for a potential volume difference between bitstream and PCM.

+1. There is definitely a volume difference between my PS3 outputting LPCM vs bitstream into an Integra 9.8. On the PS3, you change it on the fly so it's esp easy to tell. I haven't measured it but I'd ventured to say it is up to 4db higher for bitstream.
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post #30 of 53 Old 07-14-2009, 01:00 PM
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Sorry, but I like my bitstream. To me, Multichannel LPCM sounds flat - like it's been normalized. Bitstreaming seems more "dynamic" and "moving" like all the intended effects are in place. Sure you can turn the volume up to compensate, but everything else also sound louder. A whisper sound like a whisper and and an explosion is loud and engaging - that's how bitstream gives it to you. In LPCM, all the sounds come out flat, like the volume have been normalized for all the channels. It's not even about the "quality" of sound, but for me it sounds flat - like all the intended dynamic sound effect have been normalized. Sure all the sound would come out of each speaker at the right time at the same kind of audio "quality," but it's just not the same.
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