|
FAQ:
rec.audio.* Sources 2/99 (part 3 of 13)
10.0 CD Players, CDs, Turntables, and
LPs
10.1 What should I listen for when
evaluating a turntable or CD player?
For tape decks and turntables, beware
first of speed variations (wow and flutter). A good check for this is
Richard Strauss' "Also Sprach Zarathustra" (aka: The Theme
From 2001), which has a long, low, sustained organ note that comes in
well before the main theme starts, and is held through the first
movement. Concentrate on that. Make sure it doesn't wobble or warble.
There's also a good bit at the beginning of Pink Floyd's "The
Wall", but it doesn't go on as long, so you've got less time to
think about it. Tape decks are prone to losing high-frequency notes, so
pick something you like which has lots of treble, and make sure it is
clear.
The sound of a turntable is largely bound
up in the kind of cartridge mounted on it. Make sure to listen to a table
with a cartridge similar to what you're buying, and not one in a different
price bracket. If possible, audition the turntable with the same arm and
cartridge, so that you will experience potential cartridge/arm
interactions, too. Most cartridges work better with one arm than another.
Treat the tonearm/cartridge pair as a system, rather than independent
parts.
For CD players, try some piano music. See
if the high notes sound tinny. Also, try something which has some soft
parts, not the same as turning the volume down. Distortion for CD players
(as for other devices) is measured at a high output, but in fact in CD
players (unlike others) it's likely to be worse in soft passages of music.
Most classical recordings contain a suitable soft passage. Most rock music
won't.
Distortion in CD players, if you want to
call it that, is a function of the granulation noise, or time-delay
pre-echo that can come out of the filtering. To listen for this, use
material that is rich in high-order harmonics, such as brass music.
Unfortunately, you can't reliably predict how a CD player will sound by
looking at specifications, features, or the technology it uses. If you
want to know how a player will sound, you MUST listen to it.
10.2 Are some discs better than others?
Some recordings are better than others.
Some artists are better than others. Some recording engineers are better
than others. Some microphones are better than others. Some music is better
than others.
Ignoring that, there is some difference
between discs. Some of the very earliest discs were badly made and
deteriorated with time. The technical problems that caused those problems
have been solved.
Some "gold" discs are available
which are advertised to have better life and quality than common
"aluminum" discs. These sell for an extra US $15 or more per
disc over the cost of the same music on a common disc. Studies have shown
that there is an advantage to glass-encased, gold platters for archiving
computer data that is not error tolerant and will need to be stored for
many tens of years. I have yet to see a similar comparison which justified
any extra effort for storing audio recordings for 50 years. Part of the
reason for this is that audio recordings contain error correction codes,
allowing a CD player to perfectly reconstruct minor flaws. Another reason
is that CD players can effectively reconstruct badly damaged audio data,
even if some data is completely missing.
Some discs seem to have pinholes in the
aluminum, which are visible when the disc is held up to a strong light.
However, these discs play fine and last very well, so the effect of these
pinholes is probably nil. Some have performed studies counting errors on
various discs with various players. They found that, in general, the error
count was consistent from one player to another. Also, in general, most
discs have a low, consistent error rate which is perfectly correctable
using the redundant data stored on the disc. This study did find that one
group of discs had a higher error rate than all of the rest. This group
was the promotional discs, also called "music samplers" given
away by music companies to introduce you to their family of artists and
performers. Despite these higher error counts, these discs still played
fine.
If there is no abusive handling involved, I
have rarely heard of a disc that degraded with time. Of the few that have
existed, they tended to be from one of the bad batches mentioned earlier.
There is no doubt that some discs are
mastered better than others. Some are badly mixed. Some are so badly
recorded that there is noticeable clipping. Some are made from damaged
master recordings. CD technology is no guarantee of good music or of a
good recording. 1
10.3 Are CDs better than LPs?
Some excellent recordings are mastered
digitally, and sound great on LPs. This suggests that there is nothing
inherently bad about digital.
Some find that LPs sound better than CDs.
Advocates of LPs claim that the digital to analog (D/A) converter in home
CD players isn't up to the quality of the information on the disc. They
also claim that the analog electronics in a home CD player can be poor.
Some believe that CDs do not sound like LPs
because the CD does not have the frequency response errors, the
distortion, or the stereo separation problems of LPs.
In general, though, there are good and bad
CD players, just as there are good and bad turntables, cartridges, and
tone arms. Any ultimate comparison would require ultimate equipment, which
is unaffordable. In moderately priced systems, there will be some signal
damage from the turntable system and some signal damage from the CD
player.
LP lovers often learn the nuances of
cartridge selection, record care, and even turntable and tonearm
adjustment. They have found that the turntable will sound different if the
arm height is adjusted, if the cartridge angles are changed, and if the
tonearm wire is moved. CDs do not offer as many avenues for the home
experimenter.
However, Audio Amateur Magazine has
published modification projects for CD players; particularly for Magnavox
560 and similar European players. Audio Magazine has also published such
articles.
10.4 What turntable should I buy?
Despite improvements in motor technology,
most great turntables use belt drive. Rubber roller (idler) drive sounds
the worst.
Select a turntable with a very heavy
platter for the least wow and flutter. Give the platter a rap with your
knuckle. It should not "ring" like a cymbal. It should feel and
sound dead.
Also look for a turntable that has good
isolation from base to stylus. With the amp on and the turntable selected,
but with the turntable motor off, put an old record on the turntable,
lower the stylus onto the record, and then tap the edge of the base. Not
too hard, you don't want to send the arm flying. At worst, you will hear a
quick 'thump' followed by silence through the speakers; if you're lucky,
you'll hear nothing at all. If the sound continues beyond a quick 'thump',
the mechanical isolation is not great, and you should look at some other
make. When you perform this test, be sure to unplug the turntable power
cord.
If the turntable has a tonearm, try to
evaluate the arm, too. A good arm should be adjustable in height. A good
arm should allow cartridge adjustments. A good arm will be very rigid and
have no bearing play. A good arm should accommodate a wide range of
cartridges. Despite this, some arms work better with high compliance
cartridges, while others are at their best with low compliance. Ask.
Turntables by Denon, Dual, Linn, Michell,
Oracle, Pro-Ject, Rega, Sota, Thorens, and VPI are recommended. If you
want a turntable on a budget, consider the NAD 5120 at approx. $160.
10.5 What phono cartridge should I buy
for my older turntable?
The $30 Grado ZTE+1 is a great value for
any home user but a purist. For the purist, there are still many choices,
both moving coil and moving magnet. Each sounds slightly different, and
has its individual strengths. Moving Magnet (MM) cartridges tend to have
higher output than Moving Coil (MC) cartridges, with exception. Low Output
Moving Coil cartridges require unusual preamplification. Check with a
dealer before buying one. Some candidates:
Sumiko Blue Point $125
Denon DL-160 $125
Shure VST-V $150 (MM, Std Mount)
Audio Technica AT-95E (MM, Std Mount)
Denon DL-100 $85 (MC High Output, Std Mount)
Ortofon MC-10 Super MkI $110 (MC Low Output, Std Mount)
10.6 Will phono cartridges still be
around ten years from now?
Most likely, there will still be cartridges
available, but not in the variety available ten years ago. They will
become "Special Order" in some stores and unheard of in others.
"Pro" or "DJ"
cartridges will stay available in good supply, "Audiophile"
cartridges will stay available and very expensive, "Mid-line"
cartridges will become very scarce, and a few "Budget"
cartridges will remain available in copious supply. At the same time, some
makers will drop their cartridge lines completely.
10.7 Will LPs still be around ten years
from now?
There is a strong movement of collectors
and purists who will keep their collections and buy good used discs. Count
on these people to keep the used disc market hot for 25 years longer.
As for new music, less is being pressed
today than 20 years ago. Many popular artists are being released on LP in
parts of Europe, but availability is dependent on country. One person said
that many new LPs are available in Spain.
LP sales have increased recently in
Japan and in the UK. Polydor is now re-releasing older recordings on
vinyl, and will continue to press them as long as it is profitable.
Likewise, there are several re-releasing projects in Japan. Some are for
Jazz collectors and others are for pure analog as well as classical music
lovers. They are selling the LPs by subscription, with shipments every 2
or 3 months. Each release includes about 20 titles. Japan has released
over 100 LPs this way last year.
10.8 What about CD green pens?
In a nutshell, save your money.
A CD player "reads" information
on the disc with a laser light beam. Some believe that if you put a green
stripe on the very perimeter of the disc, then the light beam will not
reflect around inside the disc and will more clearly pick up the data.
Scientific studies of the data coming off
of the disc have failed to show any difference between a virgin disc and a
green painted disc. I have not heard of double blind listening comparisons
that have proved that there are people who can hear the difference,
although many have performed uncontrolled tests with positive results.
10.9 What about CD stabilizer rings?
In a nutshell, save your money.
The data coming off of the disc is a serial
string of ones and zeros. If this bit stream has jitter, then it may reach
the D/A converter out of sync. If this happens, then the actual analog
signal recreated will have jitter, and won't be perfectly true. The
vendors of stabilizer rings say that using these rings will reduce jitter
and make a more perfect signal. Vendors also claim that the rings can
increase the mass of a disc, making it spin more smoothly, and reducing
transient load on the power supply from the motor.
Some players will not play discs that have
stabilizer rings on them. The clamp can't handle the thickness. Other
players play ringed discs, but do not play them well, because the disc
motor was not built for the added load.
With those exceptions, scientific studies
of the data coming off of the disc have failed to show any improvement
going from a virgin to a ringed disc. I have not heard of double blind
comparisons that prove that people hear the difference, either.
10.10 What about CD spray treatments (ArmorAll
et al)?
In a nutshell, save your money.
Current wisdom is to avoid any disc coating
or spray. Some will definitely damage the disc.
There are many theories on what ArmorAll
can do to a disc. One is that it reduces static which will attract the
delicate head of the laser detector to the disc. Another theory is that
the cleaner will fill voids in the disc with silicone, thereby making it
easier to read by reducing diffraction effects.
Scientific studies of the data coming off
of the disc have failed to show any difference between a virgin disc and a
treated disc. I have not heard of double blind listening comparisons that
have proved that there are people who can hear the difference.
One of the strongest proponents of ArmorAll
issued a "recall" on his advice. He now warns that ArmorAll can
damage the disc. He also advises that you can clean ArmorAll off treated
discs with Dawn dish detergent.
10.11 Are 1-bit CD players better than
multi-bit players?
In a nutshell, they are virtually the same.
There are some excellent sounding 1-bit
players and some excellent sounding multi-bit players. Some feel that the
1-bit technology has more future because it can be improved with the
rapidly improving digital technology, while the multi-bit players improve
with slowly improving analog technology. Multi-bit also has its advocates.
All of the various D/A converters try to do
the same thing, and try to achieve the exact same ideal performance. How
well they succeed is more a function of their skill and the quality of the
parts that they buy than the technique that they use. In other words, the
architecture of a D/A converter is less important than the quality of its
implementation.
10.12 Are three lasers better than one
in CD players?
Some players have one beam, some three. All
use one laser diode to generate the beam. Three-beam is just a different
method for doing track alignment. Neither is better than the other.
There are good 1-beam players and good
3-beam players. Manufacturers want advertising claims and "More Beams
Is Better" sounded good to some marketing people. Trust your ears.
10.13 Is the BMG 11-for-1 deal good?
Yes. You have to put up with their frequent
mailings. You can elect the "POSITIVE OPTION" and not have to
answer each mailing to avoid an order. You should expect to pay
approximately $2.00 per disc for shipping and handling in the US and more
elsewhere, but even at that price and assuming that you will buy one of
their discs for $16.00, you still do well. Assuming, of course, that you
want at least 11 of the discs that they are offering for sale. Some states
requires sales tax on BMG sales, and some states tax "free"
discs, but the tax still is small compared to the discount from retail.
The BMG collection contains over 2500
discs. This includes classical, pop, jazz, and other. All BMG discs come
from the larger labels. Some rumored that BMG discs are inferior to the
discs sold in normal retail chains. This has not been substantiated. In
fact, BMG distributes their discs through retail chains, as well as
through the mail, so you may get a BMG disc either way. BMG has a web
site. There is also a great CD Club FAQ on the web. Try these sites:
http://www.bmgmusicservice.com
ftp://ftp.netcom.com/pub/ra/ramseyms/cd/CD_Club.FAQ
10.14 What should I do if there is a
problem dealing with BMG?
The number to reach BMG is 317-692-9200.
Their people have been very cooperative with me and others. It is always
good policy to confirm any phone call with a letter, restating the problem
and the resolution you were promised over the phone. It is good practice
to write down the name of the person you speak with. You can also contact
BMG by FAX at 317-542-6090.
If BMG sends you something that you didn't
order, DON'T OPEN THE PACKAGE. Write REFUSED on the package and put it
back in the mailbox. They will accept the return and credit your account
for any charges.
BMG has hired a marketing firm to send out
information on the classical club. Call 800-264-9555, but don't expect
customer service from this number.
10.15 How do I get out of the BMG
racket?
If you have taken any discs from BMG, you
must either return what you have ordered or fulfill the terms of your
original agreement. This often means buying one disc at full price and
paying for the shipping on all discs you ordered and received.
Once you have done this, you can quit the
club at any time. Take your next order form and mark it with a bold marker
in large letters "CANCEL MEMBERSHIP" and mail it to: BMG COMPACT
DISC CLUB, PO BOX 91413, INDIANAPOLIS, IN 46291 USA. It may take a month
to fully take effect, but they will honor your request. While waiting for
the cancel order to take effect, be sure to return all future order forms
marked the same way. Otherwise, you may wind up with unwanted discs.
10.16 How do I get the most out of BMG?
Only buy one disc at full price, fulfilling
your obligation. Request the "POSITIVE OPTION" so that you save
on postage. Only buy from special fliers. Every month, except November and
December, they send out a "Two for half price then one free"
flier. They have almost all of the stuff in the regular fliers. They even
offer "Buy one get two free" sometimes. Wait for those special
deals. You can even order discs from an October catalog using the order
form that came in the February catalog.
You can get even more out of BMG by signing
up, getting 8 discs for the price of one, quitting, signing up again, etc.
People have done this successfully. BMG reserves the right to deny
membership to anyone, so you run a very slight risk of being denied
membership the 20th time. However, I have never heard of anyone ever being
denied membership for any reason.
The file CDClubFAQ.txt explains more than
you ever wanted to know about the BMG and Columbia music clubs. It is
available by FTP from: ftp.netcom.comin/pub/ra/ramseyms/cd or by gopher
at: biogopher.wustl.eduAn
HTML version can be found at: http://www.blooberry.com/cdfaq/
Online BMG and CH Popular Catalogs are
available at: gopher://biographer.wustl.edu or http://biogopher.wustl.edu:70/1/audio/bmg
Online BMG Classical Catalog is available
by FTP from: ftp.gmd.dein/music/cd-catalogs Get
filebmg-classical-collection_2ed.gz
10.17 What are the differences between
multibit and Bitstream/MASH Analogue to Digital converters (16-bit
vs 1-bit CD players)?
Audio data is stored on CD as 16-bit words.
It is the job of the digital to analogue converter (DAC) to convert these
numbers to a varying voltage. Many DAC chips do this by storing electric
charge in capacitors (like water in buckets) and selectively emptying
these buckets to the analogue ouput, thereby adding their contents. Others
sum the outputs of current or voltage sources, but the operating
principles are otherwise similar.
A multi-bit converter has sixteen buckets
corresponding to the sixteen bits of the input word, and sized 1, 2, 4, 8
... 32768 charge units. Each word (ie sample) decoded from the disc is
passed directly to the DAC, and those buckets corresponding to 1's in the
input word are emptied to the output.
To perform well the bucket sizes have to be
accurate to within +/- half a charge unit; for the larger buckets this
represents a tolerance tighter than 0.01%, which is difficult. Furthermore
the image spectrum from 24kHz to 64kHz must be filtered out, requiring a
complicated, expensive filter.
Alternatively, by using some digital signal
processing, the stream of 16-bit words at 44.1kHz can be transformed to a
stream of shorter words at a higher rate. The two data streams represent
the same signal in the audio band, but the new data stream has a lot of
extra noise in it resulting from the word length reduction. This extra
noise is made to appear mostly above 20kHz through the use of
noise-shaping, and the oversampling ensures that the first image spectrum
occurs at a much higher frequency than in the multi-bit case.
This new data stream is now converted to an
analogue voltage by a DAC of short word length; subsequently, most of the
noise above 20kHz can be filtered out by a simple analogue filter without
affecting the audio signal.
Typical configurations use 1-bit words at
11.3MHz (256 times over-sampled), and 4-bit words at 2.8MHz (64 times
oversampled). The former requires one bucket of arbitrary size (very
simple); it is the basis of the Philips Bitstream range of converters. The
latter requires four buckets of sizes 1, 2, 4 and 8 charge units, but the
tolerance on these is relaxed to about 5%.
MASH and other PWM systems are similar to
Bitstream, but they vary the pulse width at the ouput of the digital
signal processor. This can be likened to using a single bucket but with
the provision to part fill it. For example, MASH allows the bucket to be
filled to eleven different depths (this is where they get 3.5 bits from,
as 2^(3.5) is approximately eleven).
Lastly it is important to note that these
are all simply different ways of performing the same function. It is easy
to make a lousy CD player based around any of these technologies; it is
rather more difficult to make an excellent one, regardless of the DAC
technology employed. Each of the conversion methods has its advantages and
disadvantages, and as ever it is the job of the engineer to balance a
multitude of parameters to design a product that represents value for
money to the consumer.
All sampling techniques (so also D/A
techniques) require an analog reconstruction filter following the
converter. This filter inherently adds phase shift, frequency response
ripple and high frequency roll-off, depending on the characteristic of the
reconstruction filter (which depends on the position of its poles and
zeros).
An oversampling data converter generates a
higher output sampling rate than a simpler converter, so you can use a
more simple reconstruction filter, which is cheaper and more stable in
time and temperature and produces less noise. Also, modern oversampling
systems include digital filters which compensate the response of the
analog filter in the passband, so you can achieve systems with an overall
performance of 20 Hz...18 kHz +/-0.05 dB. Also deemphasis is mostly done
in the digital domain.
So the "sound" of a CD player is
more than just the number of bits. It's the quality of the converter, the
filter requirements imposed by that converter, the quality of the filter,
and of course, the quality of the following analog components. Power
supply quality and clock jitter also influence the sound.
10.18 What is the best under-$200 CD
player?
In this price range, most manufacturers
give you more features than construction quality or sound quality. If you
want a particular feature, then use that to guide your purchase. If you
are after the best possible sound quality, let your ear be your guide.
Sound quality still varies among models. Don't trust reviews or advice
alone.
10.20 What is the best under-$500 CD
player?
Some recommend Rotel. Others recommend
Marantz, NAD, or Yamaha. The industry has made major gains in terms of
sound consistancy in the past years. However, models change every year and
there are models with design flaws. Let your ear be your guide. Also,
don't forget to check quality of construction. In this price range, you
should get more than a flimsy box and more durable mechanisms than in the
<$200 price range.
10.21 (removed)
10.22 (removed)
10.23 How can I clean a dirty CD?
Use a drop of dish detergent and lots of
clean water. Do not rub. Never rub or wipe in a circle. If you must stroke
the disc do it with a soft cotton cloth in a straight line from the center
outwards (radially). Rinse the disc in running clear water, shake off most
remaining drops, and lightly pat dry with a soft, clean cloth.
10.24 Can you repair a damaged CD?
If the disc is lightly scratched on the
bottom, then you can polish out the scratch and probably repair the disc
perfectly. If there are lots of scratches or deep scratches, or there is
damage on the top, you may be facing a lost cause. The music information
is immediately under the label. If you scratched the reflective layer, the
disc is normally unrecoverable.
Before trying any repair, try washing the
disc with clear water and a bit of liquid dish detergent. Do not scrub or
rub hard. Rinse the disc with clear water and shake off as much water as
you can. Finally, wipe the last few drops off with a soft, clean cloth, in
a radial direction.
SMALL scratches can be removed with a
scrufty T-shirt and toothpaste, such as Tom's Toothpaste.
You may wish to try a thin coating of
Johnson's Klear floor wax on the bottom of the CD. Often it will cover the
scratches enough to allow playing. The refractive index is pretty close to
polycarbonate, so filled scratches will be nearly invisible.
You can buy professional plastic polishing
compounds at many hobby shops. The ones used for polishing acrylics,
plexiglas, etc. work. Ordinary lapidary jeweler's polishes also work.
You'll need a rough polish to remove the scratches, then tin oxide to
polish to a mirror finish. Telescope lens kits also work. Novus plastic
polish and cleaner has been recommended. T-Cut, a car paintwork polish,
works well for big scratches. Reviewers at Audio Magazine recommend the
"Memorex CD Repair And Maintenance Kit" as the best tool for
badly damaged CDs. Another recommended polish is Meguier's Plastic Polish
#17.
Sometimes, a gentle polishing will make a
disc playable even though the scratch is not fully removed. This may be
even better than complete scratch removal because it leaves more
protective plastic behind.
10.25 Can I add digital output to a
non-digital-out CD player?
Some Magnavox CD players using the Philips
chip set can be modified. Look for a SAA7220 IC. If it has one, then it
can be modified. If you have experience modifying electronic equipment,
follow this procedure:
Take pin 14 of the SAA7220 IC and remove
whatever terminating resistor is on it. Connect it through a 560 ohm
resistor to the input of a wide band pulse transformer. Tie the other
end of the primary of the transformer to ground. Pulse Engineering
PE65612, Schott Corp 6712540, and Scientific Conversions SC916-01 all
will work. Bypass the primary through a 620 ohm resistor. Connect the
output of the transformer to an RCA jack. Do not ground either side of
the RCA jack. This output is now S/PDIF compatible. (Thanks for the tip
to Positive Feedback)
10.26 What can I get in the way of a CD
test disc?
Each test disc offers something different.
Some discs contain useless filler which advertises a product or shows a
unique capability, but really doesn't help you test or improve your
system.
Many use the Hi-Fi News & Record Review
test discs. So far, these have received only positive comments.
Chesky produces 2 test discs. The first,
"Chesky Jazz Sampler Volume I" contains some excellent imaging
test signals (called LEDR), some well-recorded acoustic jazz, and other
test signals. The second, "Chesky Jazz Sampler Volume II" has
similar music & different tests.
Stereophile produces three test discs.
Denon also produces two test discs. The
first, "Digital Audio Check" is more useful for home use. The
second, "Audio Technical" is more for repair shops and test-disc
addicts.
If you are looking for test CDs, one source
of supply that stocks lots of different test CDs is:
DB Systems
Main Street
Box 460 Rindge Center NH 03461 USA
603-899-5121
10.27 How do the letters ADD on my CD
relate to sound quality?
The simple answer to this question is that
there is no relation between the three letter code and sound quality.
Those three letters refer to the recording and mastering tools used in
making the CD.
The first letter refers to the recording
process. For example, a disc labeled ADD was ANALOG recorded, where a disc
labeled DDD was DIGITALLY recorded. Analog recording means that some form
of conventional analog tape recorder was used, whether it be a two-track
home-quality recorder or a very expensive wide-tape, high-speed,
multi-track recorder. Digital recording could be as simple as a two-track
DAT recorder, or can be a much fancier multi-track digital recorder.
The second letter refers to the recorder
used in the mixing and editing process. Mixing and editing is the process
of combining a multi-track master recording, setting levels, editing out
defects, adjusting equalization, and creating a two-track final tape.
There are good machines available for this which are analog and good
machines which are digital.
The third letter refers to the final
master, which for a CD is always digital. I have seen discs that are
labelled as AAD, ADD, DAD, and DDD.
Future releases may not have this three
letter code on them because they don't tell you anything that is
significant. Also, some codes have been used incorrectly on some discs,
which makes the information that much more meaningless.
10.28 How can I clean LPs?
There are expensive machines for this
purpose which work very well. One popular model goes by the name Nitty
Gritty. These machines spray cleaner onto the record, work it into the
grooves, and then vacuum the cleaner and dirt out. If you are serious
about records and have lots of them, it may be a good investment for you.
If you have a more reasonable collection,
you might be happy with a good hand washing every now and then. To give
your records a good hand washing, start by preparing this wash:
1 gallon distilled water
1 gram Alconox (a laboratory detergent)
Also, get a natural bristle brush and trim
it to the correct stiffness/bristle length so that the bristles can get
into the grooves but aren't stiff enough to scratch the record. Some
record-cleaning recipies recommend alcohol. However, alcohol will leach
plasticizer from vinyl, and eventually degrade LPs. Alcohol will also
disolve the shellac of 78s, so should never touch a 78.
Lay the LP flat and pour a thin coat of the
above fluid on it. Brush the wash into the grooves with the bristle brush.
Brush in the direction of the grooves, going through all grooves. Flush
the wash and dirt off with cool, running tap water. Rinse the record with
distilled water and pat it dry with a soft, clean cotton cloth.
Also consider using a carbon fiber brush
every time you play the LP. It picks up some surface dirt and removes
static.
10.29 How do you set the stylus pressure
correctly?
Stylus tracking force is typically adjusted
at the back of the tonearm with a knob that is calibrated in grams at the
stylus tip. With the control set to zero, the stylus should sort-of float
above the record surface. The control is then increased to the number
recommended by the cartridge manufacturer.
Do not, under any circumstances, use a
lower than recommended force, as the cartridge may lose the ability to
maintain contact with the groove wall on passages of large amplitude. This
WILL result in RECORD DAMAGE.
If you want the best possible tracking and
sound quality, you will want to fine-tune the tracking force. Use a test
record and listen very carefully, or get the help of a good dealer with a
battery of instruments.
10.30 How do you set the anti-skating on
a tonearm?
If you have a recommendation or suggestion
from the tonearm manufacturer, follow their advice first. They will give
you the best starting point.
Some tonearms come with calibrated
anti-skate. The manufacturer of these tonearms has tried to calibrate the
anti-skate control so that if you match the setting of the anti-skate to
the setting of the stylus pressure, you will have nearly perfect
anti-skate. Read the manufacturer's recommendations to see if this applies
to your tonearm.
You can see gross errors in anti-skate by
looking at the stylus. If you shine a light on the front of the tonearm
while playing a record, you will be able to see whether the stylus is
centered in the stylus holder. If the stylus is biased to one side or
another while playing a record, then the anti-skate is way off.
More subtle adjustments can be made by
listening for mistracking. If you can, obtain a record with equal left
right modulation at high frequency with ascending modulation magnitude
(volume), such as the Shure ERA-III, IV, or V test record. They have five
bands of "greensleeves" played on flute, and you fiddle until
the audible breakup is equal in both channels, and adjust tracking weight
until it occurs in the highest band. This is, like other cartridge and
tonearm adjustments, easier for the experienced hand than the beginner.
Some high-end dealers have electronic
instruments which allow them to accurately adjust anti-skate and other
cartridge and tonearm parameters. If you can get this service, consider
yourself fortunate.
10.31 How else do you adjust a
tonearm/cartridge/stylus?
There are a few other critical adjustments.
Again, a good high-end dealer may be your best resource. Your ear may also
be your best test instrument.
You need a level turntable. Use a quality
carpenter's level. Some people like the Shure stylus force gage for
setting stylus pressure accurately. Other tools which are well recommended
are the Geo-disk, a good protractor, and above all, the Cart-Align, which
uses a very precise etched plastic mirror for cantilever alignment.
You'll also want to set the tracking angle.
It CAN be done by eyeball, but is best done with test instrumentation and
a record. There is also the cartridge angle, tonearm height, etc. Read the
instructions which came with your tonearm for the best specific advice for
that tonearm.
Tonearm cable is more critical than any
cable anywhere else in the signal chain. Cable capacitance directly sets
the high frequency characteristics of the cartridge. In addition, the
correct grounding of the shield is essential to minimize hum. It may be
necessary to change preamp input capacitors so that the cable/preamp
combination loads the cartridge with the right overall capacitance.
Replacing tonearm cable will have a similar effect, but may be harder to
change tonearm cable than to change preamp input capacitors. Consult the
cartridge, tonearm, and preamp manuals for specific advice. Also refer to
16.6 for more information on tonearm cable.
An excellent article on setting up a
turntable is:
Stereophile, July 1990, Pages 62-85.
10.32 Do CDs deteriorate with time? What
is their life span?
A CD consists of a polycarbonate top layer,
an aluminum (or gold) metal reflective layer, a polycarbonate bottom
layer, and some miscellaneous printing ink. Of these materials,
polycarbonate seems to be extremely stable with time provided that it is
well cared for. Do not use any liquids on a CD that contain silicones or
solvents. Do not leave CDs in sunlight or other bright light. Do not stick
labels on CDs. Do not write on CDs. Do not expose CDs to temperatures
higher than normal room temperatures. Don't leave a CD under water. Even
the top side of a CD is critical and subject to damage.
Some pressings from the early 1980s used
ink which damaged the polycarbonate top layer and eventually got into the
aluminum. These inks are not in use today. Some earlier discs were made
with imperfect sealing around the perimeter of the disc. This was evident
because the aluminum in the disc extended all of the way to the disc edge.
These discs were known to fail due to moisture getting to the aluminum and
causing it to oxidize. Modern CD factories have solved this problem as
well.
With those cautions, modern CDs will last
for more than 30 years without deterioration. Most of the CDs which were
made in 1983 are still around today and still sound good.
10.33 How much music can you possibly
cram into a CD?
The longest seen so far (reported by Stuart
Kahler) is a MiC bootleg of Depeche Mode "Evolution", at 81:09.
Next are 'No Quarter' by Jimmy Page and Robert Plant at 79:38, the
collected singles CD release by The Sisters Of Mercy at 79:30, an MCA
reissue of Steely Dan: Greatest Hits at 79:17 and a Musical Heritage
recording of Bach: Goldberg Variations at 79:02. Modern CDs are pressed
using tighter track spacing than the first CDs, because modern equipment
is capable of holding tighter tolerance than the original machines.
10.34 What are input and output levels
and impedances for signal sources, preamps, amps, etc?
We have been unable to find any formal
standard on this topic. However, there is an EIA Bulletin: EIA Consumer
Products Engineering Bulletin No 6-A (CPEB6-A) 1974, titled
"Preferred Voltage and Impedance Values for the Interconnection of
Audio Products". The key word in the title is 'Preferred'.
EIA CPEB6-A recommends 3mV at 47k ohms for
magnetic phono cartridges, 250mV at less than 10k ohms for tape and preamp
outputs, and 100k ohm minimum for tape, tuner, and amp aux inputs. The
bulletin also has information on microphones, and headphones. You can
order a copy through a technical library or directly from the EIA.
10.35 Why are turntable speeds 78 RPM,
45 RPM, etc?
The speeds were chosen because that is the
speed that resulted when you used standard parts. Electric motors rotate
at 1800 rpm, most shafts are 1/4". Those combinations with the proper
gears and idlers came out to 78 rpm. In reality it's 78.26 rpm. Tape
recorder speeds evolved the same way.
The 78.26 was standardized after electric
recording/playback occured. Prior to that, speeds were "in the
neighborhood of" 78 rpm. Some lower and some higher. 80 rpm was used
in many recordings. (Courtesy of Bill Vermillion)
10.36 Why is CD digital data written in
44.1 kHz samples?
The rate of 44.1 kHz was picked to be
compatible with existing 50 Hz and 60 Hz video-based digital audio
storage, where an integral number of frame buffers could fit in a single
horizontal scan. Quote from Watkinson and Rumsey, "Digital Interface
Handbook" 2.7.6 Choice of Sampling Rate:
"In 60 Hz [525 line, 60 Hz vertical
refresh) video there are 35 blanked lines, leaving 490 lines per frame,
or 245 lines per field for samples. If three samples were stored per
line, the sampling rate becomes 60*245*3=44.1 kHz. In 50 Hz video [625
line, 50 Hz vertical refresh), there are 37 lines of blanking, leaving
588 active lines per frame, or 294 per field, so the sampling rate
becomes 50*294*3=44.1 kHz. The sampling rate of 44.1 kHz came to be that
of the Compact Disk. Even though CD has no video circuitry, the
equipment used to make CD masters is video based and determined the
sampling rate."
The length of 74 minutes is determined by
the physical nature of the reading system. It's based on the encoding
method, the wavelength of the laser used (different wavelengths are
incompatible with current CDs) and the necessary support information.
During the development of the CD, von Karajan was alledgedly asked how
long a CD must be, to which he responded it must be long enough to hold
HIS performance of Beethoven's 9th symphony, but the parameters had pretty
much already been nailed down at that point.
10.37 What's the latest on DVD and DAD?
Check out the articles in The Absolute
Sound on the subject, from issue 112, which is also on the web:
http://www.theabsolutesound.com/dadforum-1.htm
http://www.theabsolutesound.com/dadforum-2.htm
http://www.theabsolutesound.com/dvdhope.htm
10.38 What's the latest on the
MiniDisc(tm)?
Check out the MiniDisc(tm) organization web
site for a minidisc FAQ and other MiniDisc(tm) information. http://www.minidisc.org
10.39 How can I record an LP or tape
onto a CD?
That's a complex question, but basically,
get a sound card for your computer, get some cheap software for your
computer, and follow some of the advice at:
http://homepages.nildram.co.uk/~abcomp/lp-cdr.htm |
