PCM or dolby digital output? And Why? - Canadian TV, Computing and Home Theatre Forums
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post #1 of 6 (permalink) Old 2008-01-18, 03:45 PM Thread Starter
Join Date: Nov 2004
Location: Alberta
Posts: 46
PCM or dolby digital output? And Why?

I will be connecting my DSR 505 to my new Yamaha RXV1800 reciever using a digital optical cable (Toslink).

I understand that PCM is uncompressed, whereas dolby digital signals need to be decoded by the A/V reciever.

I'm confused as to which output setting I need to use for my setup? I have a 5.1 speaker setup connected to the reciever. If the tv program is being broadcast in 5.1, do I need to have dolby digital selected in order to hear the discrete channels?

Thank you
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post #2 of 6 (permalink) Old 2008-01-18, 04:19 PM
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that is correct.

Regarding "why?", PCM contains L+R only, uncompressed. Back in the days of the 401, it was one or the other, and the L+R analog would only work on PCM. This made it quite obvious as to what was going out of the fiber.


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Last edited by gmd; 2008-01-18 at 04:22 PM. Reason: added the "why?" part.
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post #3 of 6 (permalink) Old 2008-01-18, 08:53 PM Thread Starter
Join Date: Nov 2004
Location: Alberta
Posts: 46
Ok so if I leave the setting at dolby digital output for 5.1 sound, then what happens with all the other programs with regular 2 ch stereo? Will I still get sound through the receiver, or do I have to keep switching back to PCM for regular 2 ch stereo? I sure hope I don't have to keep switching between the two output settings. That would be a big PITA.
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post #4 of 6 (permalink) Old 2008-01-18, 09:02 PM
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Nothing to worry about, leave it as is. You will get all sound output through your receiver, without switching anything.
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post #5 of 6 (permalink) Old 2008-01-18, 09:26 PM
Join Date: Apr 2003
Location: Gatineau and Ottawa
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I assume these STB behave the same as SA ones I have.

If you set it to PCM then the STB must decode the DD and MP2 audio into 2 channel PCM. This is for people who may not have DD decoding ability in their AVR (very rare these days).

If you set it to DD it will pass the DD signal without decoding. MP2 audio will be decoded to PCM. I don't believe any broadcaster sends PCM.

So to summarize if your AVR does DD set it to DD. If not set it to PCM. This setting has no effect on the analog audio outputs.
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post #6 of 6 (permalink) Old 2008-01-19, 11:50 AM
Join Date: Nov 2003
Location: Kincardine ON.
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Starchoice uses DD a their native audio format. Selecting DD outputs that native DD stream, whatver its capacity (1.0, 2.0 , 5.1, or other).
PCM downconverts 5.1 to Pro-logic, or outputs the native 1.0 as two identical channels, or 2.0 as stereo (with whatever encoding was on it).
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