From: roth@gauss.enet.dec.com (Jim Roth)
Subject: Re: Digital vs Analogue, Yet Again!
Organization: Digital Equipment Corporation
Distribution: na
Date: 28 JAN 93 09:09:01    


In article <1993Jan28.012337.15017@scott.skidmore.edu>, jreiser@scott.skidmore.edu (Jason Reiser... Asleep) writes...
>fpf@aries.gasco.com (Frank Ferguson x3584) writes:
>> 
>> ...

>Wouldn't it be nice if CD players were actually capable of anything
>approaching 95dB dynamic range!  But, sadly they fall quite short of
>this, and the numbers quoted throughout the industry are strictly
>bogus!  The following is an excerpt from The Absolute Sound,
>July/August '92 by Gerard Rejskind.

   Ahh yes, TAS, a truly reliable source of technical information.

>"DYNAMIC RANGE PROBLEMS:
>	Digital's biggest selling point is its wide dynamic range.
>Certainly it is true that most CD's do not suffer from ticks and pops
>(unless they are mistracking, a common phenomenon that usually comes
                                 ^^^^^^^^^^^^^^^^^
  Say what??  Virtually none of my CD's have ever mistracked on
  any player I've ever owned.

>as a shock to new CD owners).  In fact, digital systems have quite
>poor dynamic range.  The usual claim of over 90 dB of dynamic range is
>based on a common mathematical blunder, coupled with what may be
>outright fraud.

>	The formula for calculating the theoretical maximum dynamic
>range of a digital system is well known.  It is:
>	20 log (2^b - 1)
>where b is the number of bits in the system.  Since the CD uses 16
>bits, we can calculate the dynamic range:
>	20 log (2^16 - 1) = 96.33 dB
>	This is a very attractive figure, but the fact that some CD
>player manufacturers actually claim dynamic range _greater_ than this
>theoretical maximum should make us suspicious!  In any case, even this
>value is unattainable.  The calculation ignores the fact that all 16
>bits are not used for signal data.  The last bit is used as a parity
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>check (which alerts the error correction circuit that something is
 ^^^^^ !!!!!
>wrong with the data), and so we should do the calculation with only 15
>bits:

   Now, I've seen a lot of fanciful speculation coming from clueless
   people, but this takes the cake.

>	20 log (2^15 - 1) = 90.3 dB
>	This is still very good, but there is a problem: It expresses
>the peak-to-peak value of the noise.  The usual way we measure noise
>is by its root mean square value.  To convert, we need to subtract:
> ... more bogus number dweebing and misinformation deleted ...

   The facts are that dynamic range numbers are often meaningless,
   but for none of the reasons put forth by this character.

   That TAS will publish such garbage demonstrates that they have no
   journalistic ethics whatsoever.

>	I am not much cheered by the direction in which digital is
>moving, and every time I hear an audio executive talk about "The
>Future of Digital" I get chills.  There is some cause for optimism, I
>suppose.  The very finest players (one of which I get to hear almost
>daily) are astonishing in their ability to reproduce emotionally
>satisfying music from the best disks.

   And there you have it.  Doublespeak.  On the one hand lots of
   pseudoscientific blather about why digital *can't* work, but finally
   he *listens* and hears that digital can realize its potential after
   all.

   (And by the way, with proper noise shaped dithering, you can have
   well in excess of 96 dB of perceived dynamic range, with the
   present 16 bit linear PCM standard we have now.)

    - Jim
Xref: sparky rec.audio:18993 rec.video:16178