# Hidden drc, bitstream vs pcm



## jedispork (Jan 21, 2010)

I prefer having a 2.1 setup in the living room. However I've known for a while that there are drc issues when down mixing. So I brought out the spl meter and hooked up 5.1 and did some testing. 

I get the same readings from my sub if I switch to stereo, turn off speakers, or full 5.1. I did a similar test before and assumed my onkyo 606 did not enable drc when using phantom center. However this time I switched my ps3 to bitstream and I now get about a 10 db loss on heavy bass when I use 2.1 vs full 5.1. 

This is very frustrating. I'm trying to figure out what settings will enable drc so I can avoid them. I don't want to be forced into having surrounds or a center to get the full range of sound. If I have the ps3 set to linear pcm I cannot detect any drc with the spl meter when switching from 5.1 to 2.1.

Why does dolby (or is it the receiver makers) want to punish you for using less than 5.1 speakers? Am I safe if I let all my ps3 do the decoding instead of the receiver?

Edit: I also wanted to mention that with the ps3 you can hit the triangle during the movie and options will come up. If you select a/v settings you can quickly change drc on off and bitstream or pcm. This has been useful for my testing.


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## recruit (May 9, 2009)

By bit streaming this will allow the receiver to do the decoding rather than the PS3, but by changing to PCM you are allowing the PS3 to decode all codecs, there may well be volume differences when switching between these modes and I would suggest checking your levels with an SPL meter, when going through your AV receiver.

By drc do you mean some sort of dynamic compression?


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## jedispork (Jan 21, 2010)

Yes they enable drc compression without you knowing. I messaged Roger Dressler (the dolby guy) and this is what he said. Hoping he is ok with me reposting this. 

"You are correct that some AVRs (probably most) work as yours does. There are two places in an AVR where downmixing can happen--in the DD decoder or later in the speaker management. It used to be that it was always done inside the DD chip since that was a built-in function. When DD downmixes, it activates DRC to prevent overload. But as AVRs began to handle more 5.1 sources, like PCM from BD players, they had to handle it downstream of the decoders so that every source would be covered. That's more complicated, but they can downmix without DRC and still avoid causing overload. So it is the preferred way nowadays."

While letting the ps3 do the downmixing seems to work I have accepted that I should do full 5.1 just to be safe. It would be nice if they included stereo tracks on every movie release.


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## recruit (May 9, 2009)

Hmmm, thanks Spork, 5.1 is the preferred method with dedicated speakers for all channels even when they are Sat's


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