Some writers have technical skills, while others spin out profitable junk
for acceptance by gullible editors and readers. De-gaussing (there are no
ferromagnetic materials in a disc), polishing (introduces millions of
microscratches that distort the laser beam), and trimming (can worsen track
eccentricity or unbalance), have the potential to degrade, but not improve,
CD or DVD disc quality. If this remains an issue, Media Sciences would be
glad to participate in a controlled test on a few discs, both before and
after the "improvements", at no charge and then publish the results online.
Please contact me if you wish to participate.

As stated, power demands by optical drive servos can generate adverse
feedback to a DAC through the power supply. These servos control radial
position (affected by eccentricity/radial runout or radial offset), axial
position or focus (affected by warped or tilted discs), and spindle speed
(affected by variations in disc scanning velocity). Disc unbalance can also
adversely affect many or even all of these servos.

Other surprises await. Years ago, a group of "Golden Ears" in Hong Kong
found a dislike for audio CDs having large tangential, or "once around",
variations in reflectivity. Apparently the variations in reflected intensity
caused compensatory changes in power to the read laser through a servo that
resulted in variations in power to the DAC. High quality DACs have highly
regulated and stable voltage references that may not be present in low cost

Jerry Hartke
Media Sciences, Inc.
[log in to unmask]

> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:[log in to unmask]] On Behalf Of Tom Fine
> Sent: Tuesday, January 22, 2008 6:11 PM
> To: [log in to unmask]
> Subject: Re: [ARSCLIST] Ampex ATR-102 opinion (was MD5 Hash Generators
> More importantly, Bruce, I don't want to throw a big bucket of facts on
> the audiophillic fire here, but "de-gaussing, polishing, trimming, etc" is
> This is why I can't take those "high end audio" magazines seriously --
> they will sell advertising and write articles about this junk!
> -- Tom Fine
> ----- Original Message -----
> From: "Andrew Hamilton" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, January 22, 2008 5:58 PM
> Subject: Re: [ARSCLIST] Ampex ATR-102 opinion (was MD5 Hash Generators
> > On 1/22/08 1:42 PM, "Bruce Kinch" <[log in to unmask]> wrote:
> >
> >> One problem with the "bits iz bits" argument is that all sorts of
> >> tweaks (not just better players/DACS) change (often subjectively
> >> improving) the sound of CDs - de-gaussing, polishing, trimming, etc.
> >> One of the nice things a good DAC can do is demonstrate how a
> >> "bit-perfect" CD-R copy can sound better than the original CD, and that
> >> is truly weird.
> >
> > This is truly weird.  I thought that Dr. Dunn's/Prism Sound AES paper on
> > bit-identical CDs sounding different stated that the differences all
> > disappeared when using an external DAC.  It's the internal (to the CD
> > player) DAC which he surmised gets its quartz timing futz'd by the servo
> > arm's tracking fluctuations caused by a hard-to-read (less reflective)
> > disc. So a slow burn on compatible media might make a better reference
> > disc than a fast burn on compatible media (which might make for fewer
> > errors but sound worse (on a CD player that is using its built-in DACs)
> > and is, ironically, the better master disc!).
> >
> > _andrew