Compact Discs represent the first significant improvement in audio sound sources
since the stereo phonograph record. You don't have to be a "golden ear
audiophile" to instantly perceive the remarkable sonic improvement.
Still, one must view digital sound with the same historical perspective applied to such breakthroughs as stereo, transistor amplification and FM broadcasts. Each was demonstrably better than what preceded it. And yet each had shortcomings which were improved later on, when the initial blush faded.
Just as Bob Carver has enhanced FM reception, power amplification and the effect of stereo, so he has taken digital Compact Disc sound to its next plateau with Digital Time Lens Technology.
While hundreds of articles and reviews have been written on the digital audio recording proc ess, it is valuable to review just how the process works in theory to better appreciate the Digital Time Lens' further contribution.
Analog recording uses magnetic tape to record varying amounts of musical signal. The more musical impulses in a given passage of music, the more magnetism is imparted on that portion of tape passing the recording head.
While this recording method has given us thirty years of memorable recordings, it labors under at least five physical limitations which cause audible degradation of the signal.
1) Tape has finite limits as to the amount of energy it can record. Saturation and distortion occur when the limit is reached, yet musical dynamics extend far louder and softer than the medium can handle.
2) Magnetic tape, by its very composition, imparts some internal energy which we hear as hiss. Thus quiet parts of recordings can suffer from annoying background noise.
3) it is very hard for tape to deal with extremely high and extremely low frequencies, again due to physical realities of tape oxide composition, speed and head configuration.
4) Even if problems 1-3 are minimized, the result gets scratched into the surface of a piece of plastic and played back by letting a small diamond wiggle around in the groove. Not theoretically the best method of any stretch of the imagination.
5) Even if said grooved plastic disc is the best virgin vinyl and the wiggly diamond is a $1000 handmade cartridge on a $2000 turntable, the record can come to a bad end in seconds at the hands of
a) a five -year -old with a peanut butter sandwich, b) an inquisitive pussycat, c) your best friend after half a bottle of Cabernet.
Digital recording gets around all of these problems. The musical signal is sampled and analyzed by a computer which, in effect, impartially measures the signal with a ruler. It is recording impartial digital comments such as, "This segment is VERY loud+98dB -and goes down to 20Hz." "This segment is extremely quiet and contains a flute solo with harmonics to19,000Hz." "This segment increases in dynamics by 60dB in less than a hundredth of second, etc." Instead of trying to make a physical model of these measurements the way analog tape does, digital recording simply "prepares a report," coded in 1's and 0's much the way a floppy disc can contain the text of a book encoded in binary language.
The Compact Disc playback unit "reads" the report and changes the sound back to analog musical impulses which are fed into your hi-fi just like a tuner, cassette deck or phonograph source. Except that the digital source will be free of background hiss, contain the full range of frequencies from deepest fundamentals to almost inaudible highs and provide dynamics ranging from gossamer -soft to thunderstorm loud.
Since it's not limited by actually trying to emulate the musical signal, more sheer excitement, sonic impact and definition of individual instruments reaches your preamplifier. Unquestionably digital has proved a quantum leap ahead of previous recording and playback methods. You might compare it to a good stereo disc versus an Edison wax cylinder. That's how much better a Compact Disc can be than the average vinyl recording. Still, this wonderful process has received some qualified criticism from experts who have extremely good ears. Many professional musicians, audiophiles and audio journalists, while praising the quietness and dynamic range of Compact Discs, have often expressed a lingering disappointment in the way music itself sounds on many commercial examples. This is particularly evident when the compact disc is compared with a well -executed analog counter part. The complaint boils down to a lack of ambience and spatial detail, along with a mid range which often has been described as sounding bright, hot and harsh.
When Bob Carver received his first Com pact Disc player, he too was not prepared for the compromises in sound he heard on some discs.
The three-dimensional perspective which his analog system provided in lush abundancy on phono discs evaporated into a flat, brittle waste land. The next day, he purchased no less than 2: Compact Discs and their analog, vinyl counter parts and set about quantifying the differences.
As expected, the CD discs were quieter, exhibiting better dynamic range and richer, tighter bass. But testing uncovered two inherent flaws: 1) Different spectral energy balance. The overall frequency response was shifted on the CD towards more midrange above 400 Hz; 2) The amount of Left -minus -Right channel information versus the amount of Left -plus -Right differed by about 1.25dB between analog and digital.
It is important to understand that the Left minus -Right (L - R) component of stereo carries the three-dimensional part of sound field information, much as is done with FM stereo (refer to the section on Carver's tuner circuitry). A deficiency of 1.25dB doesn't sound like much.
But since power goes up as the square of the voltage, it means that analog records carry a whopping thirty-three percent more ambience information than digital discs. That's a noticeable reduction in three -dimensionality, imaging and other psychoacoustic factors that put the realism into music.
How does the Digital Time Lens correct these problems? Bob Carver's circuitry adjusts the ratio of L - R to L + R and restores the octave-to-octave balance originally intended by the musician and recording engineer as evidenced by the analog recording.
More specifically, Bob discovered that the L + R component of a digital disc had to be equalized somewhat differently than the L –R component of the digital disc so that it would notch the analog disc (the analog version of the name musical recording). There were two equalization curves necessary to make the digital disc sound the same, exactly the same as its analog counterpart. In addition to equalizing the L + R band and the L -R band independently, it was necessary to increase the level of the L -R band so that it would match the L -R level that was on the analog disc.
Now, since the equalizations were different for the two bands, it was necessary to introduce a time correction in the L + R band because the equalization was steeper in the L -R and so the signal would go through the L- R with a greater group delay than it would go through the L + R signal chain and would arrive out of step, so a compensating delay, just micro -seconds, is employed in the L + R signal chain so that when the two signals arrive at the matrix to be turned back into left signal and right signal, they arrive without time domain errors.
CARVER DIGITAL TIME LENS
You can't buy a better CD Player than the Carver CD Player. Impartial magazine reviews prove it. Qualified listeners prove it. Your own ears will prove it in a demo at your Carver Dealer.
Unfortunately, some of you already own Compact Disc Players. There is a solution.
The outboard Digital Time Lens adds the finishing touches of sonic accuracy and realism to Compact Digital Audio Discs. It turns an innovation into near musical perfection.
If you are willing to make a commitment to vastly improving your sound source with a Compact Digital Disc player, you should also go the short extra step that lets digital realize its true potential.
That step is a Carver Digital Time Lens, connected between your CD player and pre amplifier.
Visit your nearest Carver dealer and ask for a demonstration of how we've "focused" digital playback into a crystal-clear image of the original performance.
Input: 2 v. 50k ohms Impedance Output: 2v.
Distortion: 0.005%.
Frequency Response: 20 Hz -20 kHz Dimensions:17 1/4" wide, 4" deep, 1 1/2" high.
Line Voltage: 120 VAC 60 HZ Dither signal. 0dB - 70 dB adjustable.
CARVER DTL-200 COMPACT DISC PLAYER
CARVER DTL-50 COMPACT DISC PLAYER
The DTL-200 and DTL-50 use the latest laser pick-up systems, sophisticated over sampling and digital filtering technology, and well -engineered mechanical transport designs which ensure fast track access time and increased freedom from feedback The more samples, the more accurate the music. Carver Compact Disc Players begin with the most advanced digital-to-analog D/A translation circuitry available. Along with an audible signal ranging up to 20kHz, end less images of the signal at 40K, 80K. 160K etc.
exist which must be removed from the signal to prevent harmonic problems. Many budget model Compact Disc Players place a simple anti -imaging filter after the digital/analog converter stage. Carver uses DIGITAL filtering ahead of the D/A converter through a process called double oversampling. The signal is passed through a shift register which delays the samples. so that the weighted average of a large number of signals is generated. Through a complex process. frequency bands are sup pressed between 20kHz and 160kHz. eliminating harmonic distortion problems early on before the complicated D/A translation.
The exclusive Digital Time Lens. Both the DTL-200 and DTL-50 have the remarkable Carver Digital Time Lens to further enhance your listening enjoyment.
When Bob Carver first listened critically to CDs. he immediately detected differences between the digital version and well -mastered analog versions. (See the story of the Digital Time Lens on page 26 of this publication.) These differences continue to exist on many new Compact Disc releases. depending on the mastering facility, condition of the original tape (remember, over 80% of all CDs begin with a reel-to-reel tape master!) and engineering tastes.
The Digital Time Lens restores both the lost ambience and the octave-to-octave balance originally intended by the musician and recording engineer as evidenced by the analog recording. and enhances ambient effects found on corresponding analog discs. The result is a sound with more of the three dimensional ambient information that places us in the same space with performers.
Sometimes more is not better. If one laser pick-up is good. many manufacturers have reasoned that customers will assume that three lasers must be better. The DTL-200 and DTL-50. along with several other of the world's finest CD players. use a sophisticated single laser system. (Sometimes Less is More.) Through a beam splitting process using aerospace-grade optics, a single laser's output is received by SIX diode pick-ups and monitored through ultra-high speed servo tracers.
This approach increases Carver Compact Disc Players' ability to correct for mistracking caused by production flaws. fingerprints and dust.
DTL-200
COMPACT DISC PLAYER WITH DIGITAL TIME LENS AND TIME DOMAIN CORRECTION
14 -function infrared wireless remote
Digital Time Lens -- Time Domain Correction
12 -track programmability
The DTL-200 is replete with easy -to -use features. the latest digital -to -analog translation technology. Carver's exclusive Digital Time Lens circuitry and an important new innovation. Time Domain Correction, which can actually adjust for imperfections in digital source material and disc manufacturing! A built-in quality control computer.
Time Domain Correction constantly monitors the incoming digital signal for imperfections and "glitches:' These high frequency harmonics may be caused in the recording process.
during the incredibly intricate Compact Disc mastering process or as part of the final production of the CD. Such errors in the digital bit -stream cannot be corrected by conventional tracking correction or D/A circuitry because they are part of the actual information being read off the CD. Yet they can add to overall harmonic distortion and cause audible changes in sound quality.
The DTL-200 constantly performs a complex. 25-bit digital calculation on passing digital data. This high speed error correction code, in conjunction with a 121-pole digital filter. terminates distortion -generating high harmonics. (In effect, this circuit acts as a "121st Order Crossover." rolling off distortion products by a whopping 728dB/octave!) The result is frequency response within 1/1000 of a dB of the original and reduction of distortion to 0.007%.
The DTL-200's slim. 14-function wireless remote duplicates all front panel operations--even power on and off.
Along with the ability to skip forward or backward. song-by-song, a touch of a key allows you to audibly review a disc. backward or forward, at many times normal speed.
This is especially useful in conjunction with the DTL-200's A-B Specific Phrase Replay/ Repeat feature. If you wish to carefully analyze one section of a performance. make out indistinct lyrics or just repeat an incredible musical passage of any length repeatedly, you need only mark the beginning and end with one remote control key.
Naturally the DTL-200 also lets you repeat any specific track or a whole Compact Disc for uninterrupted enjoyment. Select as many as twelve songs from a CD in any order Delete the tracks you don't want to hear.
Repeat your favorites several times. Or just rearrange their order. For classical music lovers. the DTL-200 also has complete indexing capabilities as well.
All functions are displayed on an easy to -read but subtle LCD display including programming sequence, current selection number total CD playing time. individual track playing time and total CD elapsed time.
CARVER DTL-50 COMPACT DISC PLAYER WITH DIGITAL TIME LENS
9-function infrared wireless remote
Digital Time Lens
9 -track programmability
Most manufacturers would be content to present the DTL-50 as their top-of-the-line CD player--it's that good. Incredible sonic performance. and the equally remarkable restorative capabilities of the Digital Time Lens are brought to your ears through an impressive list of features that make CD listening an exercise in comfort and precision.
Pick up the 9 -function wireless remote control and power-up the DTL-50. It will now automatically play a pre-loaded CD while you remain in the comfort of your chair. Its Programmable Random Access Playback System makes track search and programming of up to nine different selections a snap. as is automatic repeat of a previous selection or an entire CD. The DTL-50 also features repeat of individual songs or the whole CD as well as precise index access.
Large, easy-to-use feather -touch control! include pause, fast forward and reverse. You can even monitor music at high speed to find a certain portion of a selection.
Superbly styled, sonically the equal of an) CD player on the market today. the DTL-50 offers you Carver innovation and musicality at a most affordable price.
Specifications Frequency Response: DTL-200 5Hz-20kHz @ 0dB ± 0 2dB /DTL-50 5Hz-20kHz @ 0dB +0 5dB Total Harmonic Distortion: DTL-200 0 007% @ 1kHz DTL-50 0.008% @ 1kHz S/N: DTL-200 100dB/DTL-50 96dB Channel Separation: DTL-200 90dB @ 1kHz DTL-50 86dB @ 1kHz Dynamic Range: DTL-200 100dB/DTL-50 96dB Wow & Flutter: DTL-200 Unmeasurable DTL-50 Unmeasurable Output Voltage: DTL-200 2.0V (F.S.)/DTL-50 1.9V (F.5 Size: DTL-200 3.5" H x 19" W x11" D DTL-50 2.56" H x 17.25" W x 11" D.
Weight: DTL-200 14 lbs./DTL-50 13 lbs.
(Source: Audio magazine, Oct 1986)
Also see:
The Carver Compact Disc Player (Equip. Profile, Mar. 1985)
Discrete Technology LSI Mk. II Compact Disc Player (Nov. 1986)
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