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PCM Audio

Old 11-13-07, 10:51 PM
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PCM Audio

I read Josh's audio essay in the FAQ, but I still need some clarification on PCM. I've got a PS3 outputting audio through to my reciver via Digital Optical. I set the BD Audio menu to Bitstream on the PS3, is that the best option? For discs that offer Uncompressed PCM, I can select that and my receiver seems to handle it, but I thought PCM couldn't go over optical? Also, sound appears to be coming through all 6 of my speakers, but my receiver only has 2 channels lit up (L&R). Should I really only be selecting DD 5.1 or DTS for my setup?
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Old 11-13-07, 10:59 PM
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The PS3 will downmix the PCM track and send it as 2 channels over optical.

PCM can go over optical as long as it's just two channels (and that's what good ol' CDs use), although I believe there's a limit on the sampling rate (48khz or 96khz). It's multichannel PCM that won't work.
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Old 11-13-07, 11:02 PM
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The uncompressed audio tracks will get down-rezzed when you use the PS3's optical audio output. Your owner's manual should tell you if the down-rezzed audio gets converted to DD 5.1 or dts 5.1 and sent through its optical audio output.
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Old 11-14-07, 08:53 AM
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Unfortunately the PS3 owners manual doesn't tell you jack. So is the PS3 sending 2 channels to my receiver over optical, and then my receiver is converting it back to 5.1? Or is the PS3 converting to 5.1 before it goes over optical? My receiver definitely only had 2 speakers lit up on my display, but there is sound coming out of all 6 speakers. I was watching Clockwork Orange BD, and the PCM track sounded better than the 5.1 track. The rear surrounds has more echo and ambient noise...
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Old 11-14-07, 09:05 AM
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Originally Posted by Copper Blue
Unfortunately the PS3 owners manual doesn't tell you jack. So is the PS3 sending 2 channels to my receiver over optical, and then my receiver is converting it back to 5.1? Or is the PS3 converting to 5.1 before it goes over optical? My receiver definitely only had 2 speakers lit up on my display, but there is sound coming out of all 6 speakers. I was watching Clockwork Orange BD, and the PCM track sounded better than the 5.1 track. The rear surrounds has more echo and ambient noise...
It's definitely not coming out as 5.1. You might be hearing sound from all the speakers, but I still hear sound from all the speakers when I play a Dolby 2.0 Surround track, so that's no surprise.

Unless you're running a HDMI cable from the PS3 to the receiver, you won't get the full 5.1(or 7.1) uncompressed audio. It's the one downside to the PS3. No analog inputs in the back like other Blu-ray players.
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Old 11-14-07, 09:11 AM
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Originally Posted by Copper Blue
Unfortunately the PS3 owners manual doesn't tell you jack. So is the PS3 sending 2 channels to my receiver over optical, and then my receiver is converting it back to 5.1? Or is the PS3 converting to 5.1 before it goes over optical? My receiver definitely only had 2 speakers lit up on my display, but there is sound coming out of all 6 speakers. I was watching Clockwork Orange BD, and the PCM track sounded better than the 5.1 track. The rear surrounds has more echo and ambient noise...

PCM is too bandwidth intensive for Optical. Optical has a limit of how much information it can pass through to a receiver. Its why DTS goes up to 1.5M over optical, thats the max the Optical connection can do. 2 of the PCM channels can make it through, but no more then that. For example, a typical 16-bit PCM track is 4.6M in bandwidth. Obviously If you send it via Optical there is no way to send it through. But if you do send it via optical, and you select the PCM track, you are sending 2-channels and your receiver is most likely using Dolby Pro Logic 2 on it to create the surround. You will need a HDMI receiver to get the lossless audio out of the PS3.

p.s. - Most people prefer the 2-channel PCM + ProLogic mix vs 640k dd5.1 mix.
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Old 11-14-07, 11:03 AM
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For your Blu-rays, you should try to to select the generic DD 5.1 track (the compressed one) if it's present on the disc, and send that down the optical audio output from the PS3 to get 5.1 audio.
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Old 11-14-07, 11:17 AM
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Originally Posted by Copper Blue
Unfortunately the PS3 owners manual doesn't tell you jack. So is the PS3 sending 2 channels to my receiver over optical, and then my receiver is converting it back to 5.1? Or is the PS3 converting to 5.1 before it goes over optical? My receiver definitely only had 2 speakers lit up on my display, but there is sound coming out of all 6 speakers. I was watching Clockwork Orange BD, and the PCM track sounded better than the 5.1 track. The rear surrounds has more echo and ambient noise...
Your receiver is processing the 2 channels into 6 channels, which is why you're hearing the echo. The receiver's display is telling you what the input is.

I would usually prefer the DD track to 2-channel PCM with processing because the channels are discrete, but for ACO the PCM track may be better. I think the movie was recorded in mono anyway, so the 5.1 mix is mostly to expand the music.
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Old 11-14-07, 11:18 AM
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I guess I need to go back to sound school. I always thought PCM WAS 2 channel sound.
If PCM has so much quality what cable setup gets the full bandwith to the receiver, I mean before HDMI?
I thought DTS over optical was the best sound.

an after thought is this only dealing with the output on the PS3 or is it on everything?
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Old 11-14-07, 11:33 AM
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In order to get full, uncompressed PCM audio, you can use either the analog cables, which most receivers have, or HDMI. Of course, with the analog cables, your player must have 5.1 outs on it. Not all HD DVD players have them, but I think all BD standalones do.
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Old 11-14-07, 03:11 PM
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Originally Posted by ds6161
I guess I need to go back to sound school. I always thought PCM WAS 2 channel sound.
If PCM has so much quality what cable setup gets the full bandwith to the receiver, I mean before HDMI?
I thought DTS over optical was the best sound.

an after thought is this only dealing with the output on the PS3 or is it on everything?
Before BD, AFAIK the only A/V source with multichannel PCM was DVD-Audio, with SACD using a different, but also high quality format called DSD. (Many DVDA discs use lossless compression, but it is still PCM when unpacked.) The PS3 plays SACDs but will convert DSD to PCM. However, it won't play them at all over optical, but it will play the CD layer if that's on the disc.

As Mr. Cinema said, you need to use HDMI or analog cables with a compatible receiver to hear it.
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