From: francis@cs.adelaide.edu.au (Francis Vaughan)
Newsgroups: rec.music.cd
Subject: Re: QUESTION: Why "1 bit" players
Date: 14 Aug 92 07:00:16 GMT
Reply-To: francis@cs.adelaide.edu.au
Organization: Adelaide Univerity, Computer Science

|> |>I believe that "1 bit" means that the player reads the information on
|> |>the disc 1 bit at a time, rather than 1 word (16 bits) at a time.  This
|> |>means, I think, that it is more likely to be correct (especially if it
|> |>reads each bit more than once) since there's only 1 place the info could
|> |>be misread, rather than 16.
|> |>I'm sort of guessing here, I think I heard something like this.

Basicly this is gobbledygook.

Yes, data is initally recovered in a bit serial fashion from a CD, that is in
the nature of the track format.  It is also true of 8mm data drives and DAT
drives whether used for data or sound.  It has absolutely nothing to do with
the data format used by the DA converter.  This bit serial data stream comes
off at 4.3218Mhz. It encodes EIGHT bit packets using an 11/14 EFM coding
format.  

These eight bit packets are assembled into 16 bit samples as they pass
through the Reed Solomon cross interleave error correction logic.  The data
stream is pretty well unrecognisable by now.

The final result is a 44.1 kHz, 16 bit wide, times two channels data stream. 
It is still usually encoded on a serial bus since the data rates are low and
wires and pins are expensive, but again this serial data stream has nothing
to do with one-bit or any other kind of DA type.

Every CD player ever made looks like this.  

It is only when the DA converter internals are considered that things diverge.
It is here that the terms one-bit, MASH, oversampling and the rest matter.
However it has absolutly nothing at all to do with the recovery of data
from the CD.


shaw@mercury.ece.cmu.edu (Harvey F. Shaw) wrote :

|> However, building sufficiently accurate 16-bit A/D and D/A converters is not
|> currently possible; it requires an accuracy of one part in 130,000 (or 0.5 in 
|> 2^16) which isn't currently possible for commercial applications. 

This seems to be a common misconception about the inards of the wide DAs.


No 16 bit DA is made using a ladder network.  It is however true that to get
really good accuracy takes a lot of effort.  Techinques including dynamic
element balancing, help remove many of the of the matching problems. 
Most manufacturers will guarantee monotonic transfer functions, even if they
are still a little bumpy.

The Sony CX-20017 (a very early 16 bit chip) only contains two switched
elements one 256 times the other.  An internal 20Mhz clock is used to switch
(pulse modulate) the two elements to get the 256 different levels needed from
each. The levels are combined and you get a 16 bit DAC that only requires
element matching to within 1 in 256.  It is still a compromise design, like
all others, but does not involve unrealisable manufacturing.


Fred_M_Hamilton@cup.portal.com  noted that:

> One final note:  "1-bit" D/A conversion is a marketing term.  These are all
> really 16, 18, or 20 bit converters-they take 16 bits in and output a voltage
> proportional to the 16 bit input.  They could more accurately be called
> "16 bit sigma-delta converters" (as they are known everywhere outside the
> audio marketing world).

A bit of truth worth keeping in mind.

I wrote in sci.electronics last week on this topic:

>
>One-bit/bitstream/MASH designs are simply ones that involve a different
>set of compromises to some other designs.  They require more
>computational power in the digital filtering section and uses a simpler
>analogue part.  Since we are getting better and better at making cheap
>fast digital bits, but progress is a lot slower on the analogue design
>front the one-bit designs seem to have the edge in the tradeoff game.
>They are cheaper to make and produce better results; for the moment.
>
>The ultra high end of hifi still has adherents to the more conventional
>16 bit or wider converters, claiming that if you put the money and effort
>onto these designs they sound better than the one-bit designs.  Serious money
>and effort, and you would buy an argument about the technical merits.
>High end hifi does not go by the same rules as the rest of us.


Enough for now.

						Francis Vaughan