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Pre Amps-Dolby Digital Decoding

Discussion in 'AV Receivers & Amplifiers' started by bob007, Jan 30, 2003.

  1. bob007

    bob007
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    Was on the look out for a pre amp on Monday and had a demo with TAG equipment. Now what has got me thinking is, what is actually at the heart of an av amps decoding, pre amp or separate decoder?

    I was under the impression that the decoding was done by a chip, I also thought that the chip was soley distibuted to the different manufactures by the labs at Dolby, is this correct?

    Assuming I am correct what distinguishes say the likes of TAG to a Sherwood? If both have the same DD chip I would have thought the decoding would have been the same. So do other components come in to play? Is this where the qualities should shine through on the much pricier products.



    TIA
     
  2. EvilMudge

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    There are a couple of single chip DD decoder designs licensed from Dolby, but these are usually found in DVD players and very low end equipment.

    High end gear uses a DSP program to do the Dolby and Dts decoding - it's the quality of the DSP and the associated software that has the greatest difference on sound quality.
     
  3. NicolasB

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    Dolby Digital is an algorithm - like a computer program - rather than a specific piece of hardware. Different sound processors will use different DSP chips. There is a certain amount of variation in the programming too. For example, a Meridian processor has a mode for stereo music listening called "trifield" which is unique to Meridian. They came up with the algorithm and other people aren't allowed to use it.

    The quality of the software - which obviously has to be different for different machines even if it does the same thing, in somewhat the same way that PC software has to be different from Apple Mac software - will have an influence on the sound. The choice of DSP limits what can be done too. For example the DSP currently used in Bryston and Tag McLaren AV32R processors is not powerful enough to be able to do Dolby Headphone. The DSP in the Arcam AV8 is powerful enough, but Arcam haven't yet written the software to do it. (They may or may not actually do so eventually, we don't know). However, you're right when you say that it's the components around the DSP that make the biggest difference to the actual quality of the sound. Things like the DACs, the pre-amp stage, how well the analogue circuitry is shielded from the interference generated by the digital circuitry, and many other things.
     
  4. EvilMudge

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    Dolby Headphone at the moment is not impressing me in the least - okay there is some sense of directionality of sound effects when theres a front to rear pan, but ambient sounds just appear to come from the front like everything else.
    WRT to DSPs, a faster DSP will hopefully have a lower jitter level than a slower one, as all decoded channels should get to the DACs at closer to the reference clock time than a slower one. Also better handling of delay times and bass management from a superior piece of coding should have a more quantifiable effect on sound quality than the decoding algorithm itself.
     
  5. Paul Smith

    Paul Smith
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  6. Nic Rhodes

    Nic Rhodes
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    not stictly true. Gerzon developed Trifield (with others) and then went on to work with Meridian on MLP, hence the Meridian link. Trifield I believe is licenced by a north London company. Meridian are the advocates of this excellent algorithm in the domestic market place but there are also professional licencees as well. There is nothing in theory to stop others taking out a licence but none have to my knowledge which I think is a real shame, everyone want so to their own thing like Logic7, TMS etc. Trifield takes some beating.
     
  7. Yummy Fur

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    The Beekeeper said-

    The brochure for my humble and elderly Yamaha DSP-A1 boasts the use of Trifield, but only for the Cinema DSP modes--not the music modes :rolleyes:

    Yummy Fur
     

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