LPCM vs Bitstream

[jerrym303]

It is true that the DAC of the source is irrelavent if any sort of digital signal (LPCM or bitstream) is output to the processor.

I have never tried to determine if one signal or the other sounds better/different. Speaking strictly from an empirical standpoint, I don't believe that I have ever heard anyone say that LPCM sounds better. Many say they are identical. Some say bistream sounds better.

Being a practical person, I just run my DVD player to output bitstream. As long as there are no bad side effects, I'm getting either the same or better.

[teedub21]

I'm followin' you guys now. I don't know why I was thinking by having the PS3 decode the HD audio and sending it via L-PCM that is was doing the decoding and sending an analog signal to the pre/pro.

I just bought an OPPO BDP83SE off Ebay last night, so the PS3 wont be doing any blue ray duties anyway. The next test will be to see if the dacs in the 83se sound better sending analog to the processor, or better letting the Integra 9.9 decode the digital signal. Main reason I wanted the 83se is so I can send the 2 channel analog outs to my USP1 for my 2 channel system.

[fantom]

ryan08: Are you using HDMI or optical/coax?

Optical/coax can only transmit stereo LPCM. A TrueHD or DTS:HD MA stream will downmix to stereo and then pass out to your processor. The processor then may re-expand the signal using ProLogic decoding (if you set it to do that). This is most certainly a HUGE loss in quality.

Now, if you use bitstream with optical/coax, you will get LOSSY surround sound.
TrueHD streams will come out as lossy Dolby Digital (@640kbps).
DTS HD:MA streams will come out as lossy DTS (1.5Mbps).

If you are using HDMI and the UMC-1 is not handling either MultiCh LPCM or bitstream output, then it is doing something wrong... or the user is doing something wrong. Often times with processors/AVRs it's possible to apply some weird DSP effect even to MultiCh LPCM, which you only want to do if you hate sound quality. Make sure you are using the proper connection and choosing the proper setting on the processor.

ntrain42: This is why HDMI cables have certifications. Category 1 cables were only speced to carry 1080i video and 5.1 24/192 audio (or 7.1 24/96). Cat 2 cables can handle more than 1080p. There are also new Categories for handling HDMI 1.4 content. The thing is though, if your cable is not working, there's a good chance you won't get a picture at all (or intermittent picture/sound with drop-outs / loss of sync).

Think about it. If you bitsream Dolby across HDMI and 1 bit gets changed along the way, this isn't a change of 1 bit to the waveform. The signal is compressed and 1 bit could have a hugely altering affect on the final decoded result. Plus, even if it's PCM, that 1 bit could have a huge effect on at least that sample. The loss would be noticeable, not subtle.

ntrain42.. again: The signal stays digital until it gets to the processor either way. The processor does not have special DSP chips to handle bass management in TrueHD encoded space (I think it would take a few PhD's to figure out if this is even possible and if they found a way, we'd all thank them for wasting their time). When the processor gets the encoded sound, step 1 is to decode to LPCM. At that point, the signal can run through all the bass management, DSP mode processing, EQ it wants, no matter what the incoming format was.

Oh, and it may decode to 24/96, 24/192, 32/192 or whatever. As long as it's more than the incoming signal, there is no loss. Even if your player decodes TrueHD 24/96 into LPCM 24/192, sends it over HDMI, and then your processor resamples to 32/192 for processing, there is NO loss. As long as the bitrate per sample is greater than or equal to the original, there is no quantization error (e.g. 20 -> 24 -> 32 -> 20 = same result as original).

Now, sampling rate CAN cause quantization error and lead to loss. BUT, if the rate converts to a multiple of the original, there is no loss. (e.g. 48 -> 96 or 192 = no loss from the original). If you are listening to a CD at 44.1, then you want to get 44.1 to your processor. Of course, the processor may DISPLAY 44.1 (rate of the incoming signal), and then turn around and convert the signal to 24/192 internally for processing.

The good news is that I doubt anyone can really hear 44.1 -> 48 conversion loss at 16-bit, and 44.1 -> 192 conversion would be far less noticeable. Plus, given infinite bitrate per sample, 44.1 -> 48 would have no loss (by Nyquist theorem 48khz can produce all the frequencies that 44.1khz can and then some). The loss comes from the fact that the resampling (from 44.1->48) must be quantized at some bitrate (16, 24, 32). The higher the rate, the less the loss. This slight loss can be further masked by dithering (pushing each quantization rounding error to the next sample in the stream, averaging out the error over time) or even noise shaping, which is essentially fancy dithering that pushes quantization error into the less perceivable frequencies (i.e. high frequencies). Bottom line, 16/44.1 -> 24/192 or 32/192 is only slightly less than perfect. If only CDs had been speced at 48khz...

[ryan08]

Fantom, the connection is HDMI. With bitstream set on the dvd the unit sounds great, but I can't get the read-out on the UMC to say "trueHD even though it was selected and the movie has it. I think it says "stereo 3/2 LFC". I am getting all chanels coming through, but wonder why it won't say DolbyTrueHD? When I had the output from the dvd set to PCM, I was getting "thin" sound if you will. It was lacking dynamics.

[moovtune]

Mar 2, 2010 16:22:46 GMT -5 ryan08 said:

Fantom, the connection is HDMI. With bitstream set on the dvd the unit sounds great, but I can't get the read-out on the UMC to say "trueHD even though it was selected and the movie has it. I think it says "stereo 3/2 LFC". I am getting all chanels coming through, but wonder why it won't say DolbyTrueHD? When I had the output from the dvd set to PCM, I was getting "thin" sound if you will. It was lacking dynamics.

You keep saying "DVD" in your posts. Do you mean "DVD' or "Blu-Ray"? DVD's don't have True HD so I assume you mean Blu-Ray. If not, then there's the problem

[algreen345]

I think half the point of my original post has been lost in all this talk about Bitstream vs LPCM Sound Quality.

The other point I was making is that in my setup, when I output LPCM from the Oppo to the UMC-1, I get four or five seconds of no audio before each track begins. When I output the same track over the same connection via Bistream, there is no delay.

Why is that? Has anyone else experienced the same delay?

[House]

who knows...maybe cause light travels faster???

[markd]

Mar 2, 2010 18:49:36 GMT -5 algreen345 said:

The other point I was making is that in my setup, when I output LPCM from the Oppo to the UMC-1, I get four or five seconds of no audio before each track begins. When I output the same track over the same connection via Bistream, there is no delay.

Why is that? Has anyone else experienced the same delay?

I think there are a bunch of people reporting similar issues. Make sure you add your experience to the bug database. I owuld guess that the Oppo sends a continuous stream when using bitstream, and drops the stream between tracks when using LPCM. The UMC has an issue with streams stopping and starting.

[teedub21]

It seems the UMC should be set up to maintain the last confirmed audio stream and only switch when a stream with different audio encoding comes in. Having said this, I do notice my Integra switches back and forth on cable broadcasts and during the intro to most blue ray/dvds but audio never drops out. It acquires the signal almost instantly.

[fantom]

jerrym303: The only downside to bitstream is losing out on secondary audio (PiP audio). I have heard people say PCM sounds better, but that would only be a volume thing. See Dolby signals have a "Dialog Normalization" parameter, which is supposed to be the level of normal dialog in the source media. It ranges from 31 (unity, no change) to 1 (30dB reduction in gain). This is essentially like turning your volume down automatically and causes no reduction in dynamic range or compression of any kind. It is simply meant to make dialog fall at a consistent volume across multiple sources. For this reason, LPCM might be louder than bitstream at the same volume level. And in A/B testing, louder always wins. But neither has a loss of quality due to this.

ryan08: I'm not sure about the UMC readout. It's certainly possible the UMC is still a bit buggy. If you are actually hearing a distinct difference, then something is going wrong somewhere. I can only guarantee that LPCM vs. bitstream SHOULD not have any sound quality difference, discernible or otherwise.

If it's thin, it sounds more like you're getting a 2ch downmix in LPCM mode. You're not running through anything else first are you? TVs will handle HDMI audio, but like to downmix to 2ch before doing anything with it. And since you're not seeing TrueHD, I'm wondering if you're only getting lossy Dolby Digital in bitstream mode. Meaning it's possible you might even be able to get something better. Also check if your source is doing any sort of dynamic range compression.

algreen345: Certainly the way players/processors handle HDMI handshake and stream syncing issues differs, not only between players, but between different formats. A processor really needs to do all it can to be as accommodating as possible. It seems the UMC has a ways to go with LPCM.

[moovtune]

"OK I called EMO yesterday because I could not get TrueHD sound to work. Nick told me to try switching from pcm to bitstream on my DVD and it should show up on the menu. I did and the sound is much better, however the read-out still won't say TrueHD when I try to select it."


Another possibility is that secondary audio is turned on in the Blu-Ray player. In that case, even if you selected True HD, you only get a lossy Dolby Digital "mix" of the film sound with secondary audio. If there is no secondary audio, but you have it turned on in the player, you'd still get the lossy DD.

[loopinfool]

Don't forget that in the "Advanced Playback" settings you can set up completely different sound processing modes for each input type.

For example, you could have Dolby HD set to Stereo and MultiPCM set to PLIIx.
That would sure make it sound different when switching between bitstream and PCM!

- LoopinFool

[LCSeminole]

fantom, I want to thank you for your the breakdown of LPCM as opposed to Bitstream. I just want to be sure I'm interpreting what you've said so far.

My Panasonic DMP-BD80 blu-ray player has the options of "bitstream" & "pcm" for both Dolby TrueHD & DTS-HD MA. If I select "bitstream", then the player sends the DolbyTrueHD or DTS-HD MA track to the decoder in the UMC-1 to be unpacked to "pcm" and then allows for bass management.

If I select "pcm" in the player, then the decoder in the player unpacks the DolbyTrueHD or DTS-HD MA track to pcm and sends that to the UMC-1 for bass management.

So if I'm interpreting correctly, then the difference is if you want the processor to do the decoding then use "bitstream" and if you want the player to do the decoding then you want "pcm". So assuming this is correct, there shouldn't be any difference in sound as to what does the decoding, the player or the UMC-1?

Everyone please feel free to correct me where I may have not interpreted correctly.

[littlesaint]

Mar 3, 2010 19:32:23 GMT -5 LCSeminole said:

fantom, I want to thank you for your the breakdown of LPCM as opposed to Bitstream. I just want to be sure I'm interpreting what you've said so far.

My Panasonic DMP-BD80 blu-ray player has the options of "bitstream" & "pcm" for both Dolby TrueHD & DTS-HD MA. If I select "bitstream", then the player sends the DolbyTrueHD or DTS-HD MA track to the decoder in the UMC-1 to be unpacked to "pcm" and then allows for bass management.

If I select "pcm" in the player, then the decoder in the player unpacks the DolbyTrueHD or DTS-HD MA track to pcm and sends that to the UMC-1 for bass management.

So if I'm interpreting correctly, then the difference is if you want the processor to do the decoding then use "bitstream" and if you want the player to do the decoding then you want "pcm". So assuming this is correct, there shouldn't be any difference in sound as to what does the decoding, the player or the UMC-1?

Everyone please feel free to correct me where I may have not interpreted correctly.

100% correct.

[mcg]

Mar 3, 2010 19:32:23 GMT -5 LCSeminole said:

fantom, I want to thank you for your the breakdown of LPCM as opposed to Bitstream. I just want to be sure I'm interpreting what you've said so far.

My Panasonic DMP-BD80 blu-ray player has the options of "bitstream" & "pcm" for both Dolby TrueHD & DTS-HD MA. If I select "bitstream", then the player sends the DolbyTrueHD or DTS-HD MA track to the decoder in the UMC-1 to be unpacked to "pcm" and then allows for bass management.

If I select "pcm" in the player, then the decoder in the player unpacks the DolbyTrueHD or DTS-HD MA track to pcm and sends that to the UMC-1 for bass management.

So if I'm interpreting correctly, then the difference is if you want the processor to do the decoding then use "bitstream" and if you want the player to do the decoding then you want "pcm". So assuming this is correct, there shouldn't be any difference in sound as to what does the decoding, the player or the UMC-1?

Everyone please feel free to correct me where I may have not interpreted correctly.

You pretty much have it right.

You can't really "process" a bitstream....you have to unpack it first. At which point the processor is now "looking at" the exact same PCM stream as would be sent by a player if it did the unpacking.

If a processor can only apply post-processing to a bitstream and not a LPCM stream, then that is a limitation of the processor and deliberate decision by the engineers.

At the end of the day, this whole bitstreaming business is a red-herring as you can see. The only practical difference will be a light on your pre-pro indicating TrueHD or whatever.

In fact, with bitstreaming your functionality may very well be reduced, as the BR format is intended to actively mix different sources into the LPCM stream before sending it over to your processor. Secondary tracks, PiP, and such (as fantom mentioned) need to be sent via LPCM from the player, as opposed to a bitstream...I'm pretty sure that players can't take secondary streams and encode them into a bitstream. So for any advanced BR feature, I believe you are limited to LPCM anyway.

[LCSeminole]

Gentlemen, Thanx for confirming what I had originally thought but wasn't 100% sure. I personally don't care if a processor like the UMC-1 lights up as "DolbyTrue HD" or "DTS-HD MA" as long as I know I'm getting the lossless track in it entirety. I now look forward to putting a UMC-1 in my home theater to put it through its paces.

[Mike Ronesia]

Heeeuuuwww! Now that that's figured out lets all take a lunch break.

[fantom]

I think the only real issues here are:

1. The UMC (according to posts here, I don't own one) is not properly displaying TrueHD or DTS HD when that is the incoming bitstream. Whether or not the UMC is doing the right thing, this is confusing and should certainly be fixed (unless it's user error, and even then, perhaps the interface could be made easier).

As has been pointed out, a DSP (or Advanced Playback) effect may be applied to the incoming stream, causing significant differences to the processing. I know my Onkyo displays both the incoming format as well as the processing mode if you cycle thru the display. Perhaps the UMC only shows one or the other?

Setting defaults such as Dolby to Dolby, Stereo to stereo, and MultiCh LPCM to, well you get the idea is always a good practice in case someone comes along and switches a mode on you at some point. At least next time the unit is powered up, you'll be back to the "correct" setting.

2. The UMC does not yet handle the quirks of various streams from various players well. That is, it sometimes takes much longer to sync depending on which stream type is used.

Both of these things confuse the user, but the good news is that both should be able to be fixed in future fw updates.

I'm sure the UMC is an amazing piece of hardware with stellar sound quality. I know I'd be pissed if the interface prevented me from (or made me unsure if I was) fully utilizing what I had paid for.

[moe]

Mar 4, 2010 14:58:24 GMT -5 fantom said:

I think the only real issues here are:

1. The UMC (according to posts here, I don't own one) is not properly displaying TrueHD or DTS HD when that is the incoming bitstream. Whether or not the UMC is doing the right thing, this is confusing and should certainly be fixed (unless it's user error, and even then, perhaps the interface could be made easier).

As has been pointed out, a DSP (or Advanced Playback) effect may be applied to the incoming stream, causing significant differences to the processing. I know my Onkyo displays both the incoming format as well as the processing mode if you cycle thru the display. Perhaps the UMC only shows one or the other?

Setting defaults such as Dolby to Dolby, Stereo to stereo, and MultiCh LPCM to, well you get the idea is always a good practice in case someone comes along and switches a mode on you at some point. At least next time the unit is powered up, you'll be back to the "correct" setting.

2. The UMC does not yet handle the quirks of various streams from various players well. That is, it sometimes takes much longer to sync depending on which stream type is used.

Both of these things confuse the user, but the good news is that both should be able to be fixed in future fw updates.

I'm sure the UMC is an amazing piece of hardware with stellar sound quality. I know I'd be pissed if the interface prevented me from (or made me unsure if I was) fully utilizing what I had paid for.

My umc displays true hd and dts master with bitream from ps3 or oppo.

[ratmice]

Mar 4, 2010 15:56:03 GMT -5 moe said:

My umc displays true hd and dts master with bitream from ps3 or oppo.

Mine, too. In fact, the last thing I saw on the display this morning was:

"TrueHD 3/2 + LFE 192kHz"