# Bitstream or linear pcm?



## acommonsoul (Jan 30, 2008)

I have a ps3 hooked up to my brand new Onkyo 705...My question is, what is the difference between bitstream and linear pcm? What setting, on the PS3 will give me the best sound?.....Thanks


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## eugovector (Sep 4, 2006)

Take the example of a Dolby Digital signal on a DVD. This is a compressed format, it takes 10mb of info and squeezes it down to 1mb (numbers totally made up, actual compression ratio varies). So, in order turn a 1mb chunk of Dolby Digital into audio you can hear, it needs to be uncompressed back into 10mb.

That decompression, or decoding, can usually take place in one of two locations, 1) the dvd player, or 2) your receiver. When it is decoded in the player, 10mb of linear PCM will be sent to your receiver and then played with no further decoding. When it is decoded in the receiver, the player sends out 1mb of bitstream output, which is turned into 10mb in the receiver.

So, which sounds best? Well, if your AVR doesn't decode the bitstream format you're sending it (Dolby TrueHD for instance), you won't get any sound at all, until you switch to Linear PCM. Now, your 705 will decode DDTHD and many other codecs, so why wouldn't you want to just send everything bitstream?

Well, on Blu-ray movies, the menus have little button clicks and swooshes. These are only audible when the decoding is done in the player, these sounds are mixed in, and the whole mess is sent out Linear PCM. If you won't miss the clicks and boops, allowing your receiver to do the decoding can be a simpler setup.


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## bobgpsr (Apr 20, 2006)

The PS3 can not send the new codecs (DD+, dts-HD HR, Dolby TrueHD, or dts-HD MA) out as raw bitstream. It can do so for the legacy DD and dts codecs.

Likely best to set the Onkyo to receive linear PCM via HDMI and let the PS3 do all the codec decoding.


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## eugovector (Sep 4, 2006)

Yep, as a non-PS3 owner, I totally missed that. PCM is your best option.


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## acommonsoul (Jan 30, 2008)

Thanks a lot guys. I learn new things everyday!!Thanks again


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## MatrixDweller (Jul 24, 2007)

For plain Dolby Digital and DTS I can't hear a difference when switching from LPCM to bitstream and vise versa. The only thing it does is change the display on my 4306 to say Dolby Digital or Multi Channel etc. 

BTW the PS3 will send plain DTS if using bitstream when viewing a DTS MA HD audio track. This would be less desirable than the actual lossless audio if using LPCM.


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## Wayde (Jun 5, 2006)

My panny BD player is setup to bitstream to my receiver but it alsosends the menu sounds... swooshes and all. My AVR (Marantz 8002) tells me when the source is sending PCM or it's internally decoding a codec and exactly what it's decoding.

I guess that might be why sometimes I see sound coming as "pcm" instead of bitstream from the BD player. I have a little PCM led on the AVR that tells me and sometimes it's activated while navigating discs... I didn't even realize it was a kind of inconsistency. I must have that setup to dynamically switch in the BD player.

I must admit it was one happy day for me the first time I saw that DTS HD MA led config come up on my AVR. I had waited so long to see it.


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## yourgrandma (Oct 29, 2007)

PS3 must use bitstream and will now decode all codecs.


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## MatrixDweller (Jul 24, 2007)

As far as I knew the PS3 (I have one) doesn't pass the re-encoded bitstreams. Let me know if I'm wrong because that woud be way cool. I'm in the understanding that the PS3 will decode everything and pass it as LPCM only over HDMI.

As far as the ARV light coming on for PCM Wayde. Don't the bitstreams get decoded into PCM in the AVR?


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## Moonfly (Aug 1, 2008)

MatrixDweller said:


> As far as the ARV light coming on for PCM Wayde. Don't the bitstreams get decoded into PCM in the AVR?


I'd be interested in the answer to this. Is LPCM a transmission meathod or a final decoded audio format

It ultimately boils down to the compressed audio on the disc getting decoded and uncompressed, but does an AVR decompress bitstreams and play the audio or is all decoded data then considered LPCM meaning an avr decompresses/decodes a bitstream into LPCM and outputs this. Which of the following is correct:

Compressed audio on the disc - player decodes into LPCM and transmits - AV setup plays LPCM

or

Compressed audio on the disc - player transmits info as undecoded bitstream - AV decodes and plays bitstream audio
or
Compressed audio on the disc - player transmits info as undecoded bitstream - AV decodes bitsream - AV plays decoded bitsream out as LPCM audio.


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## muzz (Nov 30, 2006)

yourgrandma said:


> PS3 must use bitstream and will now decode all codecs.


What?

PS3 must be set to PCM to send all codecs uncompressed, it doesn't bitstream all IIRC.


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## acommonsoul (Jan 30, 2008)

I have now tried both bitstream and linear pcm and how found that everyone was correct that menu sounds don't come through on the bitstream.


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