R ¥VcDIGITAL TIME LENS TECHNOLOGY

AND COMPACT DISCS.

groove. Not theoretically the best method byany stretch of the imagination. 5) Even if saidgrooved plastic disc is the best virgin vinyl andthe wiggly diamond is a $1000 handmade car-tridge on a $2000 turntable, the record cancome to a bad end in seconds at the hands ofa) a five-year-old with a peanut butter sandwich,b) an inquisitive pussycat, c) your best friendafter half a bottle of Cabernet.

Digital recording gets around all of theseproblems. The musical signal is sampled andanalyzed by a computer which, in effect, impar-tially measures the signal with a ruler. It isrecording impartial digital comments such as"This segment is VERY loud+98dB -and goesdown to 20Hz." "This segment is extremelyquiet and contains a flute solo with harmonicstol9,OOOHz." "This segment increases indynamics by 60dB in less than a hundredthof second, etc."

Instead of trying to make a physical modelof these measurements the way analog tapedoes, digital recording simply "prepares areport," coded inTs and O's much the waya floppy disc can contain the text of a bookencoded in binary language,

The Compact Disc playback unit "reads"the report and changes the sound back to ana-jog musical impulses which are fed into your hi-fijust like a tuner, cassette deck or phonographsource. Except that the digital source will be freeof background hiss, contain the full range of fre-quencies from deepest fundamentals to almostinaudible highs and provide dynamics rangingfrom gossamer-soft to thunderstorm loud.

Since it's not limited by actually trying toemulate the musical signal, more sneer excite-ment, sonic impact and definition of individualinstruments reaches your preamplifier. Unques-tionably digital has proved a quantum leapahead of previous recording and playback meth-ods. You might compare it to a good stereo discversus an Edison wax cylinder. That's how muchbetter a Compact Disc can be than the averagevinyl recording. Still, this wonderful erocess has

Compact Discs represent the first signifi-cant improvement in audio sound sources sincethe stereo phonograph record. You don't have tobe a "golden ear audiophile" to instantly per-ceive the remarkable sonic improvement.

Still, one must view digital sound with thesame historical perspective applied to suchbreakthroughs as stereo, transistor amplificationand FM broadcasts. Each was demonstrably bet-ter than what proceeded it. And yet each hadshortcomings which were improved later on,when the initial blush faded.

Just as Bob Carver has enhanced FMreception, power amplification and the effectof stereo, so he has taken digital Compact Discsound to its next plateau with Digital Time LensTechnology.

While hundreds of articles and reviews havebeen written on the digital audio recording proc-ess, it is valuable to review just how the processworks in theory to better appreciate the DigitalTime Lens' further contribution.

Analog recording uses magnetic tape torecord varying amounts of musical signal. Themore musical impulses in a given passage ofmusic, the more magnetism is imparted on thatportion of tape passing the recording head.

While this recording method has given usthirty years of memorable recordings, it laborsunder at least five physical limitations whichcause audible degradation of the signal. 1) Tapehas finite limits as to the amount of energy it canrecord. Saturation and distortion occur when thelimit is reached, yet musical dynamics extend farlouder and softer than the medium can handle.2) Magnetic tape, by its very composition,imparts some internal energy which we hear ashiss. Thus quiet parts of recordings can sufferfrom annoying background noise. 3) it is veryhard for tape To deal with extremely high andextremely low frequencies, again due To physicalrealities of tape oxide composition, speed andhead configuration. 4) Even if problems 1-3 areminimized, the result gets scratched into the sur-face of a piece of plastic and played back byJetting a small diamond wiggle around in the

received some qualified criticism from expertswho have extremely good ears. Many profes-sional musicians, audiophiies and audio jour-nalists, while praising the quietness and dynamicrange of Compact Discs, have often expressed alingering disappointment in the way music itselfsounds on many commercial examples. This isparticularly evident when the compact disc iscompared with a well-executed analog counter-part, The complaint boils down to a lack ofambience and spatial detail, along with a mid-range which often has been described as sound-ing bright hot and harsh.

When Bob Carver received his first Com-pact Disc player, he too was not prepared for thecompromises in sound he heard on some discs.The three-dimensional perspective which hisanalog system provided in lush abundancy onphono discs evaporated into a flat, brittle waste-land. The next day, he purchased no less than 23Compact 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 inherentflaws: 1) Different spectral energy balance. Theoverall frequency response was shifted on theCD towards more midrange above 400 Hz- 2)The amount of LefMnimis-Iiighf otimm informa-tion versus the amount of Left-pius-Ufght differedby about 1.25dB between analog and digjtai.

It is important to understand that the Left-minus-Rigm (L - R) component of stereo carriesthe three-dimensional part of sound field infor-mation, much as is done with FM stereo (referto the section on Carver's tuner circuitry) Adeficiency of 125dB doesn't sound like much.But since power goes up as the square of thevoltage, it means that analog records carry awhopping thirty-three percent more ambienceinformation than digital discs, Thaf s a noticeablereduction in three-dimensionality, imaging andother psychoacoustic factors that put fne realisminto music.

How does the Digital Time Lens correctthese problems? Bob Carver's circuitry adjusts

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c A R V Rtie ratio of L - R to L + R and restores thectove-fo-octave balance originally intendedy the musician and recording engineer asivtdenced by the analog recording.

More specifically, fob discovered that the+ R component of a digital disc had to be

iquaiized somewhat differently than the L - R,omponent of the digital disc so that it would

match the analog disc (the analog version of theame musical recording). There were two equal-

ization curves necessary to make the digital discound the same, exactly the same as its analog;ounterpart. In addition to equalizing the I + Riand and the L - R band independently, it wasieeessary to increase the level of the L - R bando that if would match the L - R level that was onhe analog disc.

Now, since the equalizations were differentor the two bands, It was necessary to introduce

a time correction in the L + R band because theequalization was steeper in the L - R and so thesignal would go through the L - R with a greatergroup delay than it would go through the L + Riignal chain ond would arrive out of step, so a

compensating delay, just micro-seconds, isimpioyed in the L + R signal chain so that whenhe two signals arrive at the matrix to be turnedback into left signal and right signal, they arrivewithout time domain errors.

Tf» DtaHa! I n t e lens. Theory one! Practice.Bob Carver, along with many others, was dis-

pleased by the sound of the earliest CD's and decided tofind out why some didn't sound the same as the LP ver-sions of the same recordings. Unlike many who havecomplained about poor stereo Imaging, iacK of depthand strident, harsh treble-and who have blamed theCD digital system itself—Carver was enough of a math-ematician and engineering theorist to Know that the sys-tem itself was inherently blameless.

After extensive comparison tests between LP's andheir CO versions, which included time-synched playings

of both types of record while measurements and obser-vations were made. Bob concluded that there were twomajor differences between certain CD's and their LPequivalents. The first had to do with stereo depth or sep-aration, in any stereo program, the stereo effect is trans-mitted by the difference between Sett end right signals.Bob discovered that many CD's have less relative L - Rinformation trtsn do the LP's for the some programs at;he same musical moment.

in this type of display, a straight, thin diagonal linefrom the lower left to the upper right would represent apurely monophonic signal. The more stereo "difference"information there is, the more the line spreads out intoan ellipse.

Notice that there is significantly more difference(L - R) signal in the LP version of the music!

The second major difference noted by Bob Carverbetween some CD's and their LP counterparts was adifference in equalization, or the overall frequencyresponse. Using a fine moving-coil cartridge to pksy theLP versions of certain programs, Carver noted that therewas a slight BOOST in the mid-bass region and a slightCUT in the mid-treble region compared with the responseobtained when playing the CD version of the sameprogram.

Bob's objective in designing the Digital Time Lenswas to give the user the ability to introduce the converseof the two effects at will. That essentially is what he hasdone: If there is a deficiency of L-R signal in some CD's,the user can interpose a form of mafnx-demairix cir-cuitry that will put back some of the extra L-R signal. Ifthere is overly bright mid-treble ond somewhat dimin-ished mid-bass in a CD, the user can add a little mid-bass and attenuate some mid-treble frequencies bymeans of a switchabie circuit. L.F.

Reprinted by permission from Audio Magazine, © CBSPublications, 1985.

If you have read the excerpt from Audio Maga-zine included on this page, you will note that thereviewer qualified his comments by noting thatnot all CD's need the beneficial effect of theDigital Time Lens.

We concur. Later on in the review, the samereviewer noted, "I suspect that many owners will... put little marks on their CDs that indicatewhether they should be played with the TimeLens or not. I find nothing wrong with such anarrangement."

Again, we concur. It took a lot of courage onBob Carver's part to play the part of the truthfulchild confronted with the Emperors's newclothes, the part of the person with the courageto point out that digital could often sound better.

But unlike a mere critic, Bob Carver hasdone something about the shortcomings he per-ceived. He has given every music lover the finaltool necessary to open up an exciting new worldof sound.

In order to see it, Bob devised a special test circuitthat wouW amplify the difference. The figures show theLissajous patterns obtained from the same instant ofmusical program in its LP (fig B2) and CD (fig B3)versions.

F ig D?— L<sse<ousp a t t e r n s h o w i n g(L - R)/ (L + R) ratiofrom an LP record.

Fig. B3—The same instantof music as in Fig. B2 buttaken from the CDversion. Note thedecreased difference(L - R) content, asshown by the narrowedtrace.

CARVER DIGITAL TIME LENSYou can't buy a better CD Player than the

Carver CD Player. Impartial magazine reviewsprove it. Qualified listeners prove it. Your ownears will prove it in a demo at your CarverDealer.

Unfortunately, some of you already ownCompact Disc Players. There is a solution.

The outboard Digital Time Lens adds thefinishing touches of sonic accuracy and realismto 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 Com-pact Digital Disc player, you should also go theshort extra step that lets digital realize its truepotential.

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 theoriginal performance.

input: 2 v. 50k ohmsImpedance Output: 2 v.Distortion: 0.005%.Frequency Response: 20 Hz-20 kHzDimensions: XTW wide, 4" deep, 1f t ' high.Line Voltage: 120 VAC 60 HZ Dither signal: OdB. - 70 dBadjustable.

-f~ALL SPECIFICATIONS OR FUNCTIONS SUBIECT TO CHANCE WITHOUT NOTICE, j -

THE CARVER COMPACT DISC PLAYERWITH DIGITAL TIME LENS

How logical it is for a company dedicatedto delivering music with maximum dynamicimpact to offer a state-of-the-art CD player. Any-one who ever wondered why Carver makesamplifiers capable of delivering hundreds ofwatts of power need wonder no longer afterthey have heard the Carver Compact DiscPlayer as a sound source.

There are dozens of brands of CompactDisc players available right now. many of themrushed to market as "me too" line extensionswith little regard for the finer technical points ofdigital playback technology. Carver was in nohurry. They wanted to do digital right.

Because the state of the art has advancedconsiderably since the first players appearedseveral years ago. Unlike many of the "off-brand" models now available which employ lessadvanced technology, the Carver Compact DiscPlayer makes use of the latest triple laser beampick-ups and sophisticated oversampling anddigital filtering technology.

Except for features like display and pro-gramming, the real determining factor in CDplayer quality is its ability to reconstruct musicfrom digital information bits. And that is notan easy job nor one that can be effectivelyachieved while skimping on circuitry.

The Carver Compact Disc Player readsdiscs with more precisely focused laser powerthan most other models, resulting in improvedtracking and less chance of drop-outs whendust or smudges are encountered on a CD.

Along with a potentially audible signalranging up to 20kHz. there are endless imagesof the signal at 40K, 80K, 160K etc. While theyare above the range of human hearing, theymust be removed from the signal to preventharmonic problems which could turn into audi-ble distortion. Earlier CD models placed ananti-imaging filter after the digital/analog con-verter stage. Carver uses DIGITAL filteringahead of the D/A converter through a processcalled double oversampling. The signal is passedthrough a shift register which delays the sam-ples, so that the weighted average of a largenumber of signals is generated. Through acomplicated process, frequency bands aresuppressed between 20kHz and 160kHz. elim-inating harmonic distortion problems early on

before the complicated D/A translatbn.The same oversampling process also dis-

tributes the same amount of noise over twiceas wide a frequency range, resulting in half asmuch noise in the final signal. Then after trans-lation to analog, the signal is once again filteredfor a gentle roll-off above !7kHz that imparts amore natural musical sound to the final output.

One of the important tests applied todetermine the effectiveness of digital-to-analogtranslation circuitry is the reproduction of asquare wave. When Audio Magazine applied thistest to the Carver Compact Disc Player, theirtest equipment displayed the following:

One doesn't need an engineeringdegree to recognize the accuracy of the CarverCompact Disc Player's output. The reviewerobserved that "Reproduction of a 1-ftHz digitallygenerated signal was as close to a true square wave as \have ever seen from a CD player that used digital filter-ing. (The Carver Digital Disc Player] shows a virtualabsence of phase error.''

On top of this unerring ability to producewarm, real-sounding music from the CD's digitalbits, the Carver Compact Disc Player has theremarkable Digital Time Lens circuit which canfurther enhance your listening enjoyment.

When Bob Carver received his first Com-pact Disc player, he was surprised at the soundderived from some discs. The three-dimen-sional perspective which his analog systemprovided in lush abundancy on phono discsevaporated into a flat, brittle wasteland. Afterextensive testing. Bob had uncovered twoinherent flaws in some but not all CompactDiscs:!) Different spectral energy balance. The over-all frequency response was shifted on the CDtowards more midrange above 400 Hz: 2) Theamount of Left-minus-fti§ht channel information versusthe amount of Left-plus-Bight differed by about 1.2 5dBbetween analog and digital.

Bob Carver's circuitry adjusts the ratioof L - R to L + R and restores the octave-to-octave balance originally intended by the musi-cian and recording engineer as evidenced bythe analog recording.

In addition, the L + R component of a dig-ital discs is equalized by the Digital Time Lensdifferently than the L - R component and thelevel of the L - R band is increased slightly to

enhance ambient effects found on correspond-ing analog discs.

The result is a warmer sound with more ofthe three-dimensional ambient information thatplaces us in the same space with performers.You won't need the Digital Time Lens on allCD's. But it is there when you need it. And onlyon the Carver Compact Disc Player.

Ease of operation is a hallmark of Carvercomponents and the Carver Compact DiscPlayer is no exception. A subtle but easy-to-read LCD display not only shows selectionnumber, elapsed time and total time of the CD.but also "talks" to the user. Turn on the CarverCompact Disc Player and the display asks for adisc. When the disc tray is open, the displayreminds you with an OPEN readout. When a CDhas completed playing, the multi-function dis-play reads END.

With the Carver Compact Disc Player's Pro-grammable Random Access Playback System,track search and programming of up to ninedifferent selections is a snap, as is automaticrepeat of a previous selection or an entire CD.For classical music lovers, the Carver CompactDisc Player has complete indexing capabiltiesas well.

The large, easy-to-use feather-touch con-trols include pause, fast forward and reverse.You can even monitor music at high speed tofind a certain portion of a selection.

If you really enjoy music, you owe it toyourself to begin your digital experience withthe only full-feature CD player that has the Car-ver touch. The only CD player that can actuallyimprove on what is already the best playbackmedium ever offered.

Audition the Carver Compact Disc Playerwith Digital Time Lens at your Carver dealersoon.

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