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Topic: Question about bitstreams over S/P-DIF (Read 6743 times) previous topic - next topic
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Question about bitstreams over S/P-DIF

Hi folks,

Just wanting to reassure myself here but when outputing the AC3/DTS bitstream from a movie on DVD from a DVD player it'll be the same on every DVD player won't it?

As in the only way the sound could be changed by the player itself would be for it to decode it, mess with it in some way, then reencode it.

I'm just disagreeing with someone on another forum who seems to think they'll sound different on different players because they use different chipsets. Even though there's no decoding happening.

Cheers

Paul.

Question about bitstreams over S/P-DIF

Reply #1 –
Yes, normally. Some players though like the PS3 will use DD or DTS encoding on-the-fly for non-DD or DTS streams. Those players usually do it for things like bluray. I'm not sure if DVDs exist with, for instance, stereo LPCM. Even so, it probably would sound the same, unless you explicitly apply any processing available in the player (which usually don't include any EQ or such processing).

But that is probably just a hypothetical case.

In order for the decoder to get the bitstream right, the bistream has to be bit-perfect. So if the guy is saying that there's difference in audio, it's the same old "bits aren't bits when you add magic" audiophool canard.

Question about bitstreams over S/P-DIF

Reply #2 –
Indeed, if the decoding happens at your receiver then the stream MUST be the same. Else you only get pink noise.

DD and DTS are formats like mp3, i don't have a clue what happens when some bits are incorrect. Would you still get the same sound? Or is the sound different? Or will it be noise?

Question about bitstreams over S/P-DIF

Reply #3 –
I'm pretty sure you'd hear artifacts, but not a change in the audio itself as in EQ or "clarity" or whatever an audiophile might say. Any change in sound is bound to happen in the PCM domain.

Question about bitstreams over S/P-DIF

Reply #4 –
Cheers folks that what I thought. I think they'd be the same as dropouts so you'd just get weird blips in the sound?

Question about bitstreams over S/P-DIF

Reply #5 –
DD and I think also DTS frames (bitstream consists of a series of frames) are usually protected by checksums (CRCs), which are embedded into the source bitstream, and are recalculated on the receiver (=decoder) side. If for some reason a bit toggles, the tranmitted and recalculacted CRC wouldn't match, and a mute of the frame must be the result.
How the mute is actually implemented is decoder specific....In MP3 on the other hand there is either no CRC or
not the complete frame is protected by it, thus transmission errors may (!) result in weird sounds...

Question about bitstreams over S/P-DIF

Reply #6 –
Quote from: mcbear on
In MP3 on the other hand there is either no CRC or
not the complete frame is protected by it, thus transmission errors may (!) result in weird sounds...

S/P-DIF doesn't transmit mp3. It is first decoded to PCM and that is what is transmitted.

Question about bitstreams over S/P-DIF

Reply #7 –
Quote from: pdq on
Quote from: mcbear on
In MP3 on the other hand there is either no CRC or
not the complete frame is protected by it, thus transmission errors may (!) result in weird sounds...

S/P-DIF doesn't transmit mp3. It is first decoded to PCM and that is what is transmitted.

You are right for most of the available implementations of course. The SPDIF-standard foresees it however ;-)
Thus replace transmission error by read/store error or streaming error....org. question was about SPDIF though.

Question about bitstreams over S/P-DIF

Reply #8 –
Quote from: mcbear on
Quote from: pdq on
Quote from: mcbear on
In MP3 on the other hand there is either no CRC or
not the complete frame is protected by it, thus transmission errors may (!) result in weird sounds...

S/P-DIF doesn't transmit mp3. It is first decoded to PCM and that is what is transmitted.

You are right for most of the available implementations of course. The SPDIF-standard foresees it however ;-)
Thus replace transmission error by read/store error or streaming error....org. question was about SPDIF though.


Yep specifically DD/DTS transmission over S/P-DIF
 

Question about bitstreams over S/P-DIF

Reply #9 –
Quote from: pdq on
Quote from: mcbear on
In MP3 on the other hand there is either no CRC or
not the complete frame is protected by it, thus transmission errors may (!) result in weird sounds...

S/P-DIF doesn't transmit mp3. It is first decoded to PCM and that is what is transmitted.


I can setup my Cyberhome CH-DVD 505 player to pass the bitstream of MPEG audio through its S/PDIF connection ... 

as a side effect, I get excellent sound quality(*) from MP3s but no sound at all from MP2s (satellite audio streams)

(*)there's no way to ABX this tho, because I'd have to stop playback, get back in the menu, reconfigure audio output, get back out of menu and restart playback

Cheers,
Maggi