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From: shauns@vice.UUCP (Shaun Simpkins)
Newsgroups: net.audio
Subject: Re: Carver CD Player & Technology
Message-ID: <89@vice.UUCP>
Date: Fri, 8-Mar-85 13:02:15 EST
Article-I.D.: vice.89
Posted: Fri Mar  8 13:02:15 1985
Date-Received: Mon, 11-Mar-85 04:46:04 EST
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Organization: Tektronix, Beaverton OR
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> 	   {ihnp4, hplabs} hpfcla!mpm
> 
> P.S. Being rather naive about the underlying technology I would like
> some feedback on this:
> 
>      From previous discussions I have guessed that CD players incor-
> porate 4x oversampling and (usually?) digitial signal processing use
> the underlying Phillips mechanism.  I think that Phillips uses 14-bit
> converters (D-A).  Thus, apparently, there are no players that offer
> 16-bit DACs (do you need them) AND 4x oversampling.
> 
>      Frankly I don't think this conjecture makes much sense.  But with
> a degree in CS, most of the technical discussions so far have blown
> right by me.  So please help straighten me out.
> 	-- Mike "time to get back into audio equipment" McCarthy

Yes, Mike, there are 16 bit 4x oversampling CD players; they just use one
16 bit DAC per channel.  I posted something about this to the net a few months
ago.  The upshot is that data words are presented to the DAC once every
5.6us with 4x oversampling.  If you peruse your catalogs for cheapo 16-bit
DACs you will find that they settle (i.e., the output converges to within a
least significant bit of the correct value) in about 4-5us.  Thus, only one
data channel can be presented to a 16-bit DAC at a time.  DAC sharing (i.e.,
time sharing one DAC between channels with an analog sample/hold for each
channel after the DAC) effectively doubles the data rate.  Solution? Go to
14 bit DACs that settle faster if you want to use only one, or make do with
2x oversampling if you still want 16 bit conversion.  This is what Yamaha did.
I suspect that Philips made a silk purse out of a sow's ear with their 14bit
4x scheme \- at the time that chip set came out cheap 5us 16bit DACs weren't
even on the drawing board but 14 bits was within the reach of existing IC
processes.  Burr-Brown and Harris didn't report on their monolithic 16-bit
5us DACs until 1983.

Companies that make 16 bit 4x players are: Kyocera, Nakamichi, NEC.  I'm not
sure about the Carver - probably dual DAC.  16 bit 2x: Yamaha, possibly the new
Sony lines - CDP302 et al, TEAC.  14 bit 4x: Philips, Meridian, and licensees.
This list is not by any means exhaustive.  Check out your dealer and the
October issue of Audio for a more complete listing.

BTW, gramophone just reviewed the CD-X1 by Yamaha.  They almost tripped over
their tongue praising it.
Unusual for that usually kind but critical rag.

The wandering squash,
-- 
				Shaun Simpkins

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