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greg_mitch
Joined: 03 May 2006
Posts: 5320
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| Posted: Fri Jan 18, 2008 1:57 pm Post subject: Why would you "need" bitstreaming? |
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The difference between the A30 and A35 is that the A35 bitstreams the advanced audio codecs. Why would I need to bitstream?
Is it just so that people can get their new receiver to display DTS HD MA?
Perhaps the receiver or pre/pro has better bass management that works only with the bitstream audio?
I am a bit confused. Same with the Pany BD30k.
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Person99
Joined: 09 Mar 2006
Posts: 4899
Location: Flower Mound, TX
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| Posted: Fri Jan 18, 2008 3:20 pm Post subject: |
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It is easy to apply DSP to the bitstream. If you want to apply DSP to a PCM stream, you effectively have to get it into a "usable" format. Given this, most receivers or pre/pros will not apply DSP to a PCM stream, only to bitstreams. So, chances are, if you want (for example) a 7.1 mix from a 5.1 DD True HD source, your receiver or pre/pro is going to need the bitstream.
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Dave
A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....
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greg_mitch
Joined: 03 May 2006
Posts: 5320
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| Posted: Fri Jan 18, 2008 7:04 pm Post subject: |
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Oh, so let's say, Harman's Logic 7 can only be applied to a bitstream?
Besides increasing the channels from 2 channel or 5.1 channel sound why would one want to use a DSP.
I never understood the "concert" and "jazz" functions on my old receivers.
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Person99
Joined: 09 Mar 2006
Posts: 4899
Location: Flower Mound, TX
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| Posted: Fri Jan 18, 2008 7:52 pm Post subject: |
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| greg_mitch wrote: | Oh, so let's say, Harman's Logic 7 can only be applied to a bitstream?
Besides increasing the channels from 2 channel or 5.1 channel sound why would one want to use a DSP.
I never understood the "concert" and "jazz" functions on my old receivers. |
For me? Going 5.1->7.1 is the main reason. Some people like the other modes, like the THX processing.
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Dave
A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....
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greg_mitch
Joined: 03 May 2006
Posts: 5320
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| Posted: Sat Jan 19, 2008 4:47 am Post subject: |
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So if you have a 7.1 setup and you have an A30 and you have it set to DTS HD MA you will not hear sound from all speakers? You will just hear 5.1 sound?
I guess I see "bitstream" being thrown around as if everyone needs to make sure they have it or else but it seems like it isn't necessary to me.
Thanks for the clarification Dave.
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Welwynnick
Joined: 04 May 2006
Posts: 229
Location: Welwyn, Herts, UK
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| Posted: Wed Jan 23, 2008 3:33 pm Post subject: |
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| Person99 wrote: | | It is easy to apply DSP to the bitstream. If you want to apply DSP to a PCM stream, you effectively have to get it into a "usable" format. Given this, most receivers or pre/pros will not apply DSP to a PCM stream, only to bitstreams. So, chances are, if you want (for example) a 7.1 mix from a 5.1 DD True HD source, your receiver or pre/pro is going to need the bitstream. |
Dave, to the best of my knowledge, it's the other way round. DSP is only applied to PCM. PCM is fully decompressed and ready for reproduction. Bitstream is what’s multiplexed with the video when it comes out of the decoder. Whether DD, DTS, THD, DTS HR or DTS MA, when people talk about bitstream they really mean compressed audio. Digital signal processing doesn’t work on compressed audio – it works on decompressed – the data structure wouldn’t be correct otherwise , and there would be even more variables that the DSP would have to cope with. PCM is the lowest common denominator of all the digital audio formats, and is independent of the compression scheme used in the storage or broadcast layer.
The bitstream issue is one of my hobbyhorses. I don’t believe anyone “needs” bitstream, apart from some desperate CE marketing types; it’s kind of wrapped up with the HDMI V1.3 nonsense. There’s compressed audio on every SD, HD or BD disc, so bitstream audio must exist at some point in every system. The issue is where it should be decompressed from bitstream to PCM. In the case of lossless compressed audio like THD or DTS MA, the original PCM stream should be recovered without loss or degradation. Therefore, the logic goes, it shouldn’t matter whether it’s decompressed in the player and output as PCM, or output as bitstream and decompressed in the AVR. The result should be the same, and either way, the PCM will be D to A converted in the AVR as usual.
However, some people suggest that bitstream decoding in the amp sounds better than player decoding, and that’s many want bitstream output. But does it? I don’t think anyone, anywhere, knows for sure yet. The answer probably lies in the system-level digital audio replay architecture, and in particular how the timing information is managed. Digital audio consists of digital amplitude data and analogue timing info, and both have to right. Assuming the decompression of the amplitude data is always accurate (reasonable), that leaves differences in timing info to explain audible differences.
Several months ago I speculated that PCM may be more susceptible to jitter form poor timing info transmission, because de-compressed digital audio carries timing info from the player to the amp, but bitstream does not. Advantage bitstream.
However, HD audio of any type is carried by HDMI, and that separates out amplitude and timing info. The audio clock in the amp is tied to the video clock in the player. More recently I figured, this architecture would also apply to a bitstream connection – otherwise how does the amplifier maintain synchronisation between the audio and the video? No advantage.
Last month, I heard from Amir M that the bitstream replay architecture is indeed different to the PCM architecture, and audio timing is solely derived within the amplifier. Advantage Bitstream again.
Where now?
Dunno.
Nick
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Person99
Joined: 09 Mar 2006
Posts: 4899
Location: Flower Mound, TX
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| Posted: Wed Jan 23, 2008 6:01 pm Post subject: |
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| Welwynnick wrote: | | Person99 wrote: | | It is easy to apply DSP to the bitstream. If you want to apply DSP to a PCM stream, you effectively have to get it into a "usable" format. Given this, most receivers or pre/pros will not apply DSP to a PCM stream, only to bitstreams. So, chances are, if you want (for example) a 7.1 mix from a 5.1 DD True HD source, your receiver or pre/pro is going to need the bitstream. |
Dave, to the best of my knowledge, it's the other way round. DSP is only applied to PCM. PCM is fully decompressed and ready for reproduction. Bitstream is what’s multiplexed with the video when it comes out of the decoder. Whether DD, DTS, THD, DTS HR or DTS MA, when people talk about bitstream they really mean compressed audio. Digital signal processing doesn’t work on compressed audio – it works on decompressed – the data structure wouldn’t be correct otherwise , and there would be even more variables that the DSP would have to cope with. |
Yes, what you say makes sense. I thought most of the Receivers out did not do DSP on PCM and that was to be added with bitstream support. I may be mistaken. 
Of course, why the hell can't my receiver make a 6.1 mix out of a 5.1 analog input source, all they have to do is matrix a back channel the way they got a center channel from a stereo analog source--but they don't. So, maybe it is just bitstream handling and DSP come together as features although they are unrelated. Hmmmmm.
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Dave
A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....
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