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AVS › AVS Forum › Audio › Audio theory, Setup and Chat › definitions of terms such as pcm, mhl, dts, bitstream, lpcm, dsd Dolby hd , true hd etc.
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definitions of terms such as pcm, mhl, dts, bitstream, lpcm, dsd Dolby hd , true hd etc.

post #1 of 21
Thread Starter 
A while back I recall seeing a detailed explanation of this in some thread. Does anyone know where I might find this?
Thanks Mrfixit58
post #2 of 21
All of those terms require more than a one-sentence explanation. I think you'll do better with Google and Wikipedia etc, or a good technical book. Or maybe use the Forum Search feature here.

--Ethan
post #3 of 21
Thread Starter 
Thanks Ethan, I saw it somewhere before I just can't recall if it was on AVS or Audioholics. Somebody took the time and broke it all down.
post #4 of 21
Very quickly:

PCM (Pulse Code Modulation) is the basic digital format used for most home entertainment audio, including movies and CDs. Audio systems are engineered to process PCM to produce sound.

DSD (Direct Stream Digital) is an alternate digital format developed by Sony and used on SACDs. DSD cannot be processed by most players and receivers.

DD 5.1, DTS, TrueHD, and dts-MA are data compression codecs whose sole purpose is saving space on discs. A PCM track is fed into the encoder, which compresses it using one if those codecs. The decoder decompresses the file, turning it back into PCM. DD 5.1 and DTS are "lossy" codecs, meaning some of the data removed during encoding is not restored in the decompression phase. TrueHD and dts-MA are "lossless" codecs, meaning every bit removed by the encoder is restored by the decoder. Lossless codecs work just like zip files.

Bitstream refers to transmitting an encoded file such as DTS or DD 5.1 from a player to a receiver so that the AVR can do the decoding.
post #5 of 21
Mhl is mobile high definition link


Sent from my iPad using Tapatalk HD
post #6 of 21
post #7 of 21
Thread Starter 
Thanks for the help guys!
post #8 of 21
Quote:
Originally Posted by BIslander View Post

Very quickly:

PCM (Pulse Code Modulation) is the basic digital format used for most home entertainment audio, including movies and CDs. Audio systems are engineered to process PCM to produce sound.

DSD (Direct Stream Digital) is an alternate digital format developed by Sony and used on SACDs. DSD cannot be processed by most players and receivers.

DD 5.1, DTS, TrueHD, and dts-MA are data compression codecs whose sole purpose is saving space on discs. A PCM track is fed into the encoder, which compresses it using one if those codecs. The decoder decompresses the file, turning it back into PCM. DD 5.1 and DTS are "lossy" codecs, meaning some of the data removed during encoding is not restored in the decompression phase. TrueHD and dts-MA are "lossless" codecs, meaning every bit removed by the encoder is restored by the decoder. Lossless codecs work just like zip files.

Bitstream refers to transmitting an encoded file such as DTS or DD 5.1 from a player to a receiver so that the AVR can do the decoding.

Just a noobie add-on question to this topic: when I play my blu-ray content & send the TrueHD or dts-MA signal via HDMI through the AVR - PCM appears on my AVR.

Does that mean I am getting uncompressed lossless sound & equate to "best possible" ?

How about a TV signal through a TiVo to AVR via optical cable - that also shows PCM on the AVR screen - but from what I understand TV programming passes 5.1 or 2 Channel Stereo thus equating to PCM of lossy?
post #9 of 21
Quote:
Originally Posted by tripleM View Post

Just a noobie add-on question to this topic: when I play my blu-ray content & send the TrueHD or dts-MA signal via HDMI through the AVR - PCM appears on my AVR.

Does that mean I am getting uncompressed lossless sound & equate to "best possible" ?

How about a TV signal through a TiVo to AVR via optical cable - that also shows PCM on the AVR screen - but from what I understand TV programming passes 5.1 or 2 Channel Stereo thus equating to PCM of lossy?
If the source decodes those and sends PCM to the AVR, then you don't know the origin and hence fidelity of said samples. Check your sources to make sure they are set to "bit stream" and the AVR to make sure it has the ability to identify compressed bit streams and signal them the way.
post #10 of 21
When the source device decodes the file, you are not sending TrueHD or dts-MA to the receiver. Rather, you are sending the resulting PCM to the receiver. The AVR has no way of reporting whether the source was a lossless codec such as TrueHD or as lossy one such as DD 5.1 because the AVR doesn't have that information when the source device had already done the decoding.

If you play a lossless track and set up the device to decode that track, then you'll get the best quality possible. That is likely the case with your PS3. Your TiVo, on the other hand, is likely sending PCM that comes from a lossy DD 5.1 track since that's the best format used on HD television broadcasts. Again, it's the quality of the source that matters.
post #11 of 21
can anyone help edit this audio so I can hear what is going on? I will provide the clip
post #12 of 21
Quote:
Originally Posted by BIslander View Post

When the source device decodes the file, you are not sending TrueHD or dts-MA to the receiver. Rather, you are sending the resulting PCM to the receiver. The AVR has no way of reporting whether the source was a lossless codec such as TrueHD or as lossy one such as DD 5.1 because the AVR doesn't have that information when the source device had already done the decoding.

If you play a lossless track and set up the device to decode that track, then you'll get the best quality possible. That is likely the case with your PS3. Your TiVo, on the other hand, is likely sending PCM that comes from a lossy DD 5.1 track since that's the best format used on HD television broadcasts. Again, it's the quality of the source that matters.

So in laymen's term I interpret - in regards to most modern day BluRay movies where there is lossless audio - it as a leap of faith on the packaging of the content because everything is processed before it gets to the receiver.

& btw - true on both examples above.

Thanks for the clarification.
post #13 of 21
Quote:
Originally Posted by tripleM View Post


How about a TV signal through a TiVo to AVR via optical cable - that also shows PCM on the AVR screen - but from what I understand TV programming passes 5.1 or 2 Channel Stereo thus equating to PCM of lossy?

Is theTiVo connected to the TV? If so you probably are getting only 2 ch. stereo. Connect the TiVo directly to the AVR via HDMI. The AVR should then report DD5.1 when you are watching DD content.

TripleM, if your AVR was able to decode lossless formats then you would bitstream from the BD source and you would see the source format displayed instead of PCM.
post #14 of 21
Quote:
Originally Posted by Possumgirl View Post

Is theTiVo connected to the TV? If so you probably are getting only 2 ch. stereo. Connect the TiVo directly to the AVR via HDMI. The AVR should then report DD5.1 when you are watching DD content.

I have reasons to use optical from th TiVo to the AVR - primarily able to watch TiVO without the AVR.

That said, I believe HDMI does pass 5.1 on the TiVo to the AVR.

But in the TiVo's 2 audio settings -1) is classified 'Dolby Digital' or 2) classified as 'Dolby Digital to PCM'.

Though - I am unsure what the benefit of the TiVo doing #2 is vs. #1.
post #15 of 21
Optical is limited to two channels of PCM. So, if you set the TiVo output to DD, your receiver will be able to do the decoding and produce a discrete 5.1 output. If you set the TiVo to PCM, the TiVo will do the decoding and then downmix any 5.1 content to stereo for transmission over optical. So, set the output to DD.

As for it being a leap of faith when your PS3 decodes lossless tracks, not really. When you select the lossless track on the disc, that's what the PS3 will decode. It can't decode anything else. These days, the vast majority of BDs only have one English track. So, there's nothing to worry about.
post #16 of 21
Quote:
Originally Posted by tripleM View Post

So in laymen's term I interpret - in regards to most modern day BluRay movies where there is lossless audio - it as a leap of faith on the packaging of the content because everything is processed before it gets to the receiver.
Not quite. There are two options there: the source sends out the compressed stream to the AVR and decoding gets done there. The other option is have the player decode it and send the samples to the AVR. The math for both is the same.
post #17 of 21
One more note: the PS3 is only doing the decoding, which is nothing more than unzipping the compressed file. The receiver still handles all subsequent processing - things like bass management, room correction, and the digital-analog conversion.
post #18 of 21
Quote:
Originally Posted by amirm View Post

Not quite. There are two options there: the source sends out the compressed stream to the AVR and decoding gets done there. The other option is have the player decode it and send the samples to the AVR. The math for both is the same.

As is the sound quality.The D/A conversion either happens or it doesn't.
post #19 of 21
Quote:
Originally Posted by tripleM View Post

So in laymen's term I interpret - in regards to most modern day BluRay movies where there is lossless audio - it as a leap of faith on the packaging of the content because everything is processed before it gets to the receiver.

& btw - true on both examples above.

Thanks for the clarification.

If the player is doing the decoding,use the display or info button on it to see which track you're playing.
post #20 of 21
Quote:
Originally Posted by BIslander View Post

Optical is limited to two channels of PCM. So, if you set the TiVo output to DD, your receiver will be able to do the decoding and produce a discrete 5.1 output. If you set the TiVo to PCM, the TiVo will do the decoding and then downmix any 5.1 content to stereo for transmission over optical. So, set the output to DD.

So if I am reading this correctly, it's the optical connection piping that is limiting the source track from being delivered in whole right?

What if I set the TiVo to DD only & connect via optical- would optical be able to handle DD 5.1?
post #21 of 21
Yes, set the TiVo to output Dolby Digital. Optical supports DD 5.1 just fine.
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