Contents:
Parameter Compact Disc/CD-R
----------------------------------------------------------------------------
Full Disk diameter: 120 mm (4.75").
Disk thickness: 1.2 mm.
Disk material: Polycarbonate.
Track width: .6 micron (um) approx.
Track pitch: 1.6 microns.
Playing time (audio): 74 minutes, 15 seconds (>78 minutes by cheating)
Data capacity (CDROM): >650 MB
Sampling frequency: 44.1 KHz per channel.
Number of channels: 2.
Sample size: 16 bit linear, two's complement code.
Bit rate: 4.3218 M bits/second average (1X).
Data rate (CDROM): 150-2400 KBytes/second (1X-16X).
Spindle speed: 200 to 500 rpm (1X, constant linear velocity).
Linear speed: 1.2 to 1.4 meter/second (1X).
Modulation: Eight-to-fourteen modulation, RLL(3,11).
Error Correction: Cross Interleave Reed Soloman Code - CIRC.
Laser type: Semiconductor Diode GaAlAs.
Laser wavelength: 780 nm (most common).
Laser power: .1-1 mW. typical (at lens).
Frequency response: 5 to 20,000 Hz +/- 3 dB.
Harmonic distortion: .008 % at 1 KHz.
Dynamic range: Greater than 90 dB.
Signal to noise ratio: Greater than 85 dB.
Wow and flutter: Below measurable limit (as good as crystal).
Parameter Compact Disc/CD-R Digital Versatile Disc(k)
-------------------------------------------------------------------------
Disk diameter 120 mm 120 mm
Disk thickness 1.2 mm 1.2 mm
Disk structure Single substrate Two bonded 0.6 mm substrates
Laser wavelength 780 nm 650 and 635 nm
Numerical aperture 0.45 0.60
Track pitch 1.6 um 0.74 um
Minimum pit/land lgth 0.83 um 0.4 um
1X speed (CLV) 1.2 m/sec 4.0 m/sec
Number of data layers One One or two
Data capacity ~680 Mbyte 4.7 Gbyte (one layer)
8.5 Gbyte (two layer)
User data rate (1X) 153.6 K/sec (mode 1) 1,108 K/sec (mode 1)
176.4 K/sec (mode 2)
For more information on DVD technology, see the 16.3) A down-to-earth comparison of digital and analog recording
Digital solutions to anything are not inherently superior to old style analog
approaches. Digital storage and playback can result in truly terrible sound
if the underlying technology specifications and implementation are inadequate.
However, for storage, there is a fundamental difference which can be expressed
in simple terms:
(From: Michael A. Covington (mcovingt@ai.uga.edu)).
The way I explain digital recording to people is this:
* Digital recording is like hiring somebody to type a paper for you, from a
typed original. If they hit the same keys you did, there is no loss of
fidelity at all. If they make an error, you can find it and correct it.
* Analog recording is like hiring an artist to copy a painting. It is going
to come out a little different no matter how good they are.
16.4) What is oversampling?
CD audio reads 16 bit samples off of the disc at a rate of 44.1 K samples per
second (for each channel). This is the 1X rate. It is possible to produce
*perfectly* faithful sound reproduction at 1X. However, digital sampling
theory and the Nyquist criterion then require an analog filter which has a
flat frequency response in the audio passband - 20 Hz to 20 KHz, and 0 at
22.05 KHz (1/2 the sampling rate) and above. The filter is necessary to
remove 'aliasing' artifacts which would produce frequencies in the output
not present in the original recording. Such filters are are possible but
very difficult to design and tend to have nasty phase response as you get
near 20 KHz since the filter response needs to go from 1 to 0 within a
very small frequency range (20-22.05 KHz). The phase response may have an
effect on stereo imaging and instrument localization. Whether you can
hear any of this depends on whether you have 'golden ears' or not.
Enter oversampling. Instead of putting out the original CD samples at
44.1 KHz, digitally interpolate intermediate samples so that the D/A
converter can work at 2X, 4X, 8X or more. The digital filters can be
designed with very good performance and are part of the VLSI chipset
in the CD player. For example, with 4X oversampling, three interpolated
samples will be inserted between each original 44.1 KHz sample and
the D/A will run at 176.4 KHz. An analog antialiasing filter is still needed
at the output but its response only needs to go from 1 to 0 over the range
20 KHz to 88.2 KHz - a much much easier filter to design.
Which will sound better? There is a lot of hype. It may depend more on
the quality of either design rather than the basic technique. So many other
factors enter into the ultimate listening experience that the difference in
in frequency and phase response around 20 KHz can easily be overshadowed
by errors introduced throughout the recording process as well as playback
considerations such as speaker quality and placement, room acoustics, and
listener location.
Most consumer grade CD players now use oversampling. The newest fad is
the 1 bit D/A with 256X (or more) oversampling. This is largely
cost driven as well: you don't even need a high quality 16 bit D/A anymore.
The simplest way of describing this approach is that it is a combination
of pulse width modulation and sophisticated interpolation. The net result
is audibly the same as all the others.
16.5) What is an anti-aliasing filter
Antialiasing filters are needed in a sampled data system (of which digital
audio is one example) to guarantee that out-of-band signals do not confuse
the digitization process or find their way into the output.
1. Prior to sampling and digitizing, an antialiasing filter is used to
cut off all frequencies above Fmax where Fmax is the highest frequency
that it is desirable to reproduce. Sampling per Nyquist must be at
least at 2*Fmax but making it somewhat higher than this enables the
antialiasing filter to be more easily designed.
For example, CDs reproduce 20 KHz as Fmax and sample at 44.1 Ks/sec.
The antialiasing filter must have a response which is substantially
flat to 20 KHz and then rolls off to 0 before 22.05 KHz.
If this is not done, frequencies between 22.05 KHz and 44.1 KHz (as well
as any above) will be reflected back in the digitized samples resulting
in aliasing noise which is mighty peculiar sounding!
Thus, the signal flow for input is:
Mic or \| +-----------+ +--------------+ +---------+ +-----+ Digital
other +->+ Audio +->+ Antialiasing +->+ Sample/ +->+ A/D +--> proc.,
source /| | Amplifier | | Filter | | Hold | +-----+ storage.
+-----------+ +--------------+ +---------+
2. Following the D/A, an antialiasing filter with a similar roll off is used
to remove all frequencies above Fmax introduced by the D/A process.
Thus, the signal flow for output is:
/
+-----+ +--------------+ +-----------+ |/
Digital o-->+ D/A +->+ Antialiasing +->+ Audio +-->+ Loudspeaker
Sample | | | Filter | | Amplifier | |\
+-----+ +--------------+ +-----------+ \
The output antialiasing filter is not for antialiasing in the same sense
as the input filter (before digitization) but without it, similar audible
effects can take place in subsequent amplification stages which respond
in a non-linear fashion to any high frequency (out of band) sample or clock
noise that gets through.
3. Oversampling techniques can be used on both input and output to simplify
the filter design. Prior to the D/A, additional digital samples are
interpolated between the original samples read off of the CD. Thus, the
digital samples will typically already be at some multiple of 44.1 KHz.
The D/A then runs at a much higher sample (clock) rate decreasing the
demands on the analog filer. See the section: "What is oversampling?".
16.6) How good are the digital filters in digital audio systems?
(From: Winfield Hill (hill@rowland.org)).
The digital filters within a typical CD-sound sampling system are very good
indeed.
I'm looking at a few AES papers reprinted in the 1994 Crystal Semiconductor
databook (so we're talking "old" technology!), and I see the amazing
performance possible with the linear-phase finite-impulse-response (FIR)
filters in the delta-sigma A/D chips.
For example, the Crystal CS5328 has a flat response to 22.5kHz and then drops
like the proverbial rock to a first -105dB dip at 26kHz. Ditto for the
filters in a high-quality D/A like the CS4328.
Also, the in-band frequency response is very good. Passband ripple within
+0.00025 and -0.0004dB to 10kHz. Hmmm, deteriorating to -0.0006dB at 17.5kHz.
And for the D/A chip, a flat line on the chart (I can't see under 0.01dB) to
20kHz with a slight 0.1 dB rise by 22kHz.
Strike that "very good," insert PERFECT.
The Crystal CS5328 A/D has a very low -105dB distortion with full-scale analog
input, and -125dB with -10dB input. That works out to under 0.0005% at full
scale and even less for typical signals. The CS4328 D/A is not quite as good,
with under -92dB (0.0025%), but I'll not complain! Also, they and others
(e.g. Analog Devices) make better parts for the purist.
16.7) Instant oversampling theory
(Mostly from: Lasse Langwadt Christensen (fuz@control.auc.dk)).
When you have a signal from a CD sampled at 44.1 kHz, the resulting frequency
spectrum looks something like this after the D/A converter:
Amplitude
|
|
__|_____ ___________
| \ / \
| \ / \
--+--------+--------+-----------> Frequency
0 Fs/2 Fs Fs=44.1 kHz
After the D/A converter you then need a antialiasing filter to remove the
frequencies around the sampling frequency (Fs). That filter has to pass the
frequencies you need 0-20 kHz and remove (-96dB) the frequencies above Fs/2
(22.05 kHz). Thats a pretty sharp filter - which is a problem, since it has to
be an analog filter.
This is where oversampling come in. If you insert one zero sample in between
every real sample, you get a signal looking something like this:
where X = originally sampled values, 0 = inserted zeroes
Note: The analog signal would look like a line connecting the the X's, not
ASCII friendly :-).
Amplitude
|
|
X X
| | X X
| | | |
--+----0----+----0----+----0----+---> Time
0 1/Fs 2/Fs 3/Fs Fs=44.1 kHz
The sampling frequency has now been increased to 88.2 Khz (2X oversampling)
and in frequency it would look something like this:
Amplitude
|
|
__|_____ ___________ ____________
| \ / \ / \
| \ / \ / \
--+--------+--------+----------------+-----------> Frequency
0 Fs/2 Fs Fs*2 Fs=44.1 kHz
new_Fs=88.2 kHz
If you now filter that signal with a digital filter (before the D/A), with the
same specifications as the previous analog antialising filter, (it is a lot
easier doing it digital than analog, you get a signal something like this in
frequency:
Amplitude
|
|
__|_____ ___________
| \ / \
| \ / \
--+--------+--------+--------+--------+-----------> Frequency
0 Fs/2 Fs Fs*2 Fs=44.1kHz
And in time domain would look something like this:
Amplitude
|
|
X I X
| | | I
| | | | X I X
| | | | | | |
--+----+----+----+----+----+----+---> Time
0 1/Fs 2/Fs 3/Fs Fs=44.1kHz
As you can see from the signal in the frequency domain, the analog antialiasing
does not need to be as sharp as before, it still has to pass the frequencies
from 0-22.05 kHz but it only have to remove frequencies above 44.1kHz (the
new Fs/2). This is much much easier.
If you look at the signal, in time domain, you can see that the original
samples (X) are still where they where, but the I`s has been moved, so they
are placed as if the signal had really been sampled twice as fast. Since the
extra samples are interpolated from the original samples, are they only
limited in accuracy, by how many bits that was used in the filter. So the
signal after the digital filter could in theory be any number of bits, and
thats why a 18, 20, or 22 bit D/A-converter is sometimes used.
16.8) Is there a difference between CDs for 1X, 2X, or 25X CDROM drives?
A CD may be recorded at a 1X, 2X, 4X, etc. rate but what is on the CD is
supposed to be the same.
However, the location of the information on the disc may have been optimized
for use readout at a 1X, 2X, 4X, etc. rate on a particular drive/computer
combination but again what is on the CD is coded the same way and should be
read properly regardless of the speed of the CDROM drive. However, actual
performance including interactions with multimedia programs, and sound and
video devices may be vary dramatically.
For CDROMs, the 8X specification is not related to the 8X oversampling of
an audio player. An 8X CDROM drive can actually spin at up to 8 times the
normal speed of an audio CD. It can transfer data at 8 times the 1X (audio)
speed of 150 KB/second or about 1.2 MB/second. However, note that the actual
access time for an 8X CDROM drive may not be dramatically better than that of
a 1X drive once the seek time is taken into consideration.
A CDROM drive must get the data unaltered even with defects on the disc.
An occasional unrecoverable error on an audio CD will never be detected.
However, a dropped bit could render a program disc useless. Therefore, a
CDROM disc is coded with additional levels of error correction and a CDROM
drive has the required decoding logic to deal with this information. The
interpolation used for oversampling and the interpolation and/or muting
used for dealing with unrecoverable errors in audio players are not useful
for data. How the CDROM drive actually deals with audio playback is a
totally separate issue from its data readout performance.
For example, an 8X CDROM may actually use 4X oversampling for its audio
playback but nothing else.
Conceivably, an 8X CD ROM could buffer and read ahead - and re-read a segment
of the disc if errors are found (as some people think normal CD players do but
generally do not - at least not in the context of oversampling).
Sophisticated programs reading audio data off the CD could certainly do this
on a greater than 1X drive. I do not know whether any CDROM drives themselves
would do this given that audio performance is not something that is generally
considered that important on a CDROM drive.
An audio player using oversampling never need to spin the disc faster than
the 1X speed but implement the interpolation to simplify the analog filter
design. However, portable players with a 'bump immunity feature' have several
seconds of audio sample memory and will read (prefetch) the audio information
off of the disc at higher than 1X speed to assure that the buffer can be kept
as full as possible even if the player is unable to track for a couple of
seconds.
16.9) CDROM drive speed - where will it end?
CDROM drives advertised as 16X are now common. Taken literally, this would
mean that at the inner track, this drive must spin the CD at 500*16 or 8,000
rpm. Geez, they must have a Kevlar shield around the perimeter to catch any
shrapnel should the CD disintegrate! Have you ever seen the slow motion video
of a jet engine exploding? Just about one year ago, I was 'proving' why such
technology would never be practical. So much for predicting the future. Have
I mentioned that my crystal ball has been in the shop for the last few years
awaiting repair? :-)
However, most 16X drives really are not 16 CDROM drives.
Some drives do advertise '16X max' which might indicate a constant rotation
apeed of a much more reasonable 3,200 rpm resulting in a transfer rate which
approaches 16X only near the edge (outer tracks where 1X would be 200 rpm).
The transfer rate could be as 'low' as 6.4X near the center.
Another possibility is a hybrid approach called Partial Constant Angular
Velocity (PCAV) with a more modest 8X speed (around a constant 4240 rpm) for
the inner tracks topping off at 16X near (5/6ths of the way radially to) the
outer edge (at which point the rotation speed decreases to limit the peak
transfer rate to 16X).
12X drives typically run at a true 12X rate with the CLV varying between 6360
and 2400 rpm across the disc. These will actually have a faster transfer rate
than '16X max' drives since most discs are not full and the most frequently
accessed data is near the center - where the '16X max' drives are only really
operating at 8X.
One factor limiting the performance of present drives is the speed of the
Digital Signal Processing (DSP) chipset which is used to perform the decoding
and error handling (i.e., EFM and CIRC). This is one area where there will no
doubt be rapid advances.
There is nothing to prohibit a fully Constant Angular Velocity (CAV as opposed
to CLV or PCAV) approach from being used as long as the DSP can keep up. This
would mean that the transfer rate varies continuously across the disc. An
added bonus would be that CAV would actually greatly reduce stress on the
spindle motor and its servo system allowing for much lower cost components
and improved reliability.
There are other ways, at least in principle, of increasing the performance of
CDROM drives without spinning the discs at hyperwarp speeds. These involve
the use of multiple laser beams or entire laser pickups to read data from
multiple tracks in parallel. However, the hardware and software for these
schemes become extremely complex and expensive to implement due to the CLV
encoding, CD tolerances, and other factors. Therefore, spinning the disc
faster has become the solution of choice.
In addition, the seek time of the CDROM drive will dominate for short file
transfers. Since this specification is not as hyped as the 'X' rating, these
are often pathetic - 200 to 300 ms full stroke being typical even for high-X
(e.g., 16X) CDROM drives.
Of course, ultimately, it is the speed of the computer interface, system bus,
CPU, and software, which limits actual performance. Just because you have a
high speed CDROM does not mean it will behave as expected on your system.
There is some question as to whether discs manufactured to current tolerances
can be spun much above 6,000 rpm without vibrating themselves to pieces.
Other than this slight 'problem', there really isn't any fundamental reason
why faster drives could not be built. Perhaps, discs will simply need to be
approved for high perfomance drives (sort of like grinding wheels: "Do not
exceed 8,500 rpm") - "Do not use above 40X".
Therefore, a drive spun at a constant 8,000 rpm with an advanced DSP chipset
could operate with '30X max' performance. Are you marketers listening?
Now (August 1997) some company is offering a 24X CDROM drive!
Stay tuned for "Safety precautions and recommended body armor when using or
troubleshooting a 100X CDROM drive" :-).
On a lighter note....
For the following, if one assumes the worst case, 1X is equivalent to 500 rpm.
You can do the heavy math :-).
(From: Richard Griffin (rjgriffin@viewlogic.com)).
I just thought I would chip in with my 2 cents worth......
There have been studies into just how fast you can spin your average CD
without structural problems occurring. I believe Philips (UK) conducted the
study. They found that spinning a disc up to the equivalent of 45X caused the
disc to stretch enough due to the centripetal forces to make it impossible for
the laser to track the track (if you catch my drift). Just for the sheer hell
of it, they wound the test discs up to 56X at which point they scattered
themselves in a very artistic 'splinter' formation all over the test lab.
16.10) CDROM spins continuously even when not in use
The complaint may be that it sounds like a jet engine all the time and is
annoying or just a matter of curiosity. I don't know whether it is normal or
not for your combination of hardware and driver, but CDROM drives rated above
about 12X are typically CAV (Constant Angular Velocity) - they run at a
constant speed - not CLV (Constant Linear Velocity) like normal audio players
(though they may drop into that mode when playing audio CDs). (The X speed
rating is a MAX and you only get this performance for the outer tracks (which
may be the later files in the directory unless they specifically placed them).
Thus, your 24X CDROM drive actually spins the disc at a constant 4,800 rpm or
so and you only get the specified access times if it is already spinning.
Therefore, by one argument, it makes sense to keep it spinning whenever a data
disc is in place.
Also see the section: "CDROM drive speed - where will it end?".
16.11) Golden ears and technohype
You have no doubt encountered various claims of how player A uses
such-and-such a technology and therefore clearly has superior sound
compared, no doubt, with all others in the explored universe.
There may be people who can hear such differences in noise, frequency
response smoothness, and such. Perhaps even you could hear a difference
under ideal conditions. However, once all the variables that make *music*
are included - the chain from artist and recording studio, microphones,
recording, mixing, and resampling as well as your speakers and room
acoustics - not just sinusoids played in anechoic or resonant chambers,
the very slight differences between players are virtually undetectable
to human ears. If you are interested in playing test discs all day, then
worry about the last percentage point of noise floor or frequency response.
If you really want to enjoy the music, this stuff should not bother you.
There are more important things to worry about than an undetectable blip
in your CD player's frequency response curve. Anyhow, with the introduction
of the DVD technology pending, your carefully optimized ultimate stereo
system will be as obsolete a year from now as a 78 turntable. Consider
that! Only PC technology has a shorter lifespan. I bet you won't sleep
tonight. :-)
I would be curious as to the results of any true double-blind listening
tests comparing CD players implemented with differing technologies (analog
vs. digital filters, 4X or 256X oversampling, 1 or 2 D/As, etc.) on actual
music (not test tones) in realistic listening environmemts. Such tests
should be with people who are interested in the overall musical experience
and not just the nth decimal point of technological specsmanship. There
must, of course, be no vested interests (financial or otherwise) in the
outcome of such tests. I would bet that the results of such tests would
make for some fascinating reading and surprises for some manufacturers of
high-end audio equipment.
16.12) That last little decimal point
Someone was hyping his high-end CD player (with a stratospheric price tag
no doubt as well) claiming that it uses **mechanical** relays instead
of transistors to perform the muting function (between discs or tracks)
in the final audio amplifier. These mechanical relays are supposed to
have less capacitance and thus not affect the 'fluency' or some other
equally meaningless non-measurable characteristic of the sound. According
to the same article, "only cheap CD players costing less than $900 use
transistors for muting. All more expensive players use relays". If this
claim is true, then how can manufacturers claim a +/-0.3db response curve
from 20Hz to 20KHz even for CD players costing a lot less than $900?
Well, my 10 year old Technics SLP-2 uses relays and it sure cost a lot less
than $900. Shall we do a little calculation:
Parasitic capacitance, say 100 pF (much much larger than likely).
Highest frequency of interest: 20 KHz.
The magnitude of the impedance of this parasitic capacitance will be:
|Z|=1/(2*pi*f*C) = 1/(2*3.14159*2E+4*1E-10) = 80 K ohms
Compare this to the output impedance of a typical final audio stage, say less
than 1 K ohms (usually a lot less, but this will do for a back-of-the-envelope
calculation). Yeh, right, I will loose a lot of sleep over that. There are
better things to worry about than an immeasurable blip in your frequency
response curve: Are the transistors at the very output? Oh my gosh, you
better start investigating super ultra low capacitance audio cables costing
at least $1000 each with water protected oxygen free tapered oriented strand
conductors. But wait: you are connecting to an amplifier with non-infinite
input impedance (perhaps, horrible as it may seem, non-uniform as well)?
Your setup must sound like crap! How can you even have it in the same house
with you? There are so many variables involved in the reproduction of high
fidelity digital audio that this is about as significant as a pimple on an
elephant.
Ask for a scientifically designed and implemented A-B comparison. You
won't get one because the revelations might be too shocking for the
audio industry should the 'Golden Ears' fail to reliably distinguish
between players at the two ends of the price spectrum.
16.13) Totally worthless gadgets for CD enthusiasts
Here are descriptions of a few of the items sold to born-every-minute
suckers to improve the performance and audio quality of their stereo
systems with respect to CDs. (These are strictly CD or digital audio
related. There are many many more for general audio 'enhancement'.)
Save your money. This stuff is total garbage:
* Sonic rings to put on your CDs to stabilize them. The argument goes that
this reduces wow and flutter by helping the servo system. There is none to
begin with since pitch is determined by a quartz crystal.
Note: these may even make your performance worse due to the added inertia
of the rings. In addition, any added thickness could cause mechanical
problems with some players like Pioneer changers (cartridge type) - loading,
unloading, or during play.
* Magic markers for used on the edge to reduce errors. The rational is that
the colored edges will absorb any stray laser light and minimize interference
with the main readout beam. Forget it. Such reflections are very minimal.
Furthermore, the digital processing means that if there is a slight drop in
the signal-to-noise ratio, there will be no - zero - audible effect.
* Special digital clock you sit near your stereo to improve sound. I have no
idea of the basis for this but I heard about it on a supposedly serious audio
show. To clarify, I am talking about a time-of-day clock as in 12:34:56
with LEDs that has no direct physical connection to the audio equipment, not
some high precision atomic cesium beam time-base unit! Perhaps, the added
digital noise floating around will add some dithering to the signals and
improve linearity? Right.... :-).
* Special cleaning solutions. Soap and water just isn't good enough for
Golden Ears. No doubt, CDs should be stored under pyramids as well for
optimal longevity.
* Fiber optic patch cords to reduce phase distortion. No kidding, I am sure
there is at least one biological life-form in the universe that could
detect the nanosecond or so phase shift introduced by the ordinary copper
variety used by the rest of us. You don't suppose all the electronics
involved will introduce any distortion of its own, do you?
(From: Zev Berkovich (ah392@freenet.toronto.on.ca)).
I recently was sent one of those audiophile magazines, and out of all the
really stupid things advertised there, these two I found the funniest:
* A demagnetizing CD. Play this on your system and it is supposed to
demagnetize your equipment and make it sound better. The one I have seen
the ad for claims: 10 times the effective demagnetization of other discs.
Less than 1/100th the heat dissipation (!!!??) of other discs. Complete
demagnetization of all frequency selective circuits.
The fax I got was pretty funny. They claim on their fax that it also removes
residual magnetism from the slight impurities present in the copper wires.
(Maybe it will degauss my TV! --- sam)
Of course, the disc is made with 99.999% pure 24 karat gold (for a higher
reflected signal level, whatever that means). (This, too, is of course
bogus. Gold will have the same or lower reflectance at the IR wavelength
of the CD laser. It just looks way cool. --- sam).
* Special solder, which tells you to remove all the solder on your
amplifier, and redo all of it with this "Wonder Solder UltraClear". "For
mere pennies you can solder (or reflow) a whole amp or speaker, and make
it sound like one twice as expensive". (Sure sounds like a fun project
to me - solder reflow in your toaster oven! --- sam).
16.14) More on CD enhancers - magic markers and anti-vibration disks
(From: someone I will leave anonymous).
"I just had to comment on what you said about CD enhancers. I had the
opportunity to test both a special green magic marker and a plastic
anti-vibration disc that you stick on top of the CD to improve sound.
The magic marker didn't work but the anti-vibration plastic did work.
What I heard it do was enhance the spatial quality of the music. The
separation was better. It sounded like the various instruments were a
good foot or two farther apart on each side. That said, the demo was
conducted on a $20,000 stereo system and I felt that $50 for the plastic
disc was a bit high and I wasn't convinced that I could hear a difference
on my more modest system."
Sorry to be skeptical - go do an A/B comparison. Unless that player
has an excessive error rate - and I doubt that to be the case with a
$20,000 system - there is simply no way that any meaningful difference
is possible. A CD is not like an LP - small variations in speed are
irrelevant and thus improving the stability or whatever is also irrelevant.
The data readout is fully buffered - meaning that even if there is wow and
flutter or vibration in the CD rotation, it does not matter.
Show me a double blind A/B comparison and I will reconsider. For now, the
physics doesn't make sense.
The guy doing the demo wasn't by any chance trying to sell $50 disks, now
was he? :-)
And, no, I have not done a double blind test. But, I would not mind being
proven wrong. Just that based on the physics and technology, unless the CD
player had a high error rate to begin with due to an underdamped servo
system - he could have jimmied it - then there simply is no basis for
expecting such things to improve a digital datastream. If the error rate
decreased due to his discs, then perhaps there would be some sonic
improvement. But, it should not have been high to begin with. Error rate
reduction is the only possible mechanism I can think of to explain any
possible audible differences. However, virtually all errors due to disc
imperfections and scratches are *fully* corrected and thus undetectable in
the output by human or machine.
BTW, was he also selling $1000 speaker cables?
16.15) Why is speaker cable like spaghetti?
(From: Keith Mayes (Mayes@d-m-g.demon.co.uk)).
A survey was carried out in the 70's. People were given two bowls of
spaghetti, one coloured blue and one coloured spaghetti colour. Most
people claimed to prefer the taste of the spaghetti-coloured spaghetti.
This was a real effect, with real people who had nothing particularly
to gain or lose either way. Naturally, there was no instrumentally
measurable difference in flavour between the two types.
The same applies to speaker cables. People who have fancy cables
will quite probably hear an improved sound, in their judgement.
There is more to perceived sound quality than vibrating eardrums.
Someone who has already bought fancy cable will not appreciate this
story. If they hear an improved sound, then that's their good fortune.
Someone who is considering buying fancy cables may well benefit from
this story. It may save them a small fortune.
In reality, the Emperor's response to being told that he was naked was:
1. Deny it and prove it with signed affidavits.
2. Have the kid locked up under a section of the mental health act.
To believe in the power of a fancy cable surely pales into insignificance
beside belief in a deity, and there are plenty of people who go for that.
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