THE DYNAMIC RANGE POTENTIALOF THE PHONOGRAPH

By Ronald M. Bauman

his article describes a newapproach for analyzing thedynamic range of the phono-

graphic playback system, in which thecartridge and preamplifier are treatedas an integrated system. I analyzedthe dynamic range potential of severalcombinations of phono cartridges andpreamplifier amplifying devices andcompared the results to CDs.Additionally, I speculate about thedrawbacks of frequency domain char-acterizations of musical audio compo-nents and suggest that the timedomain may be a more natural frameof reference for audio instrumentationdevelopment.

lntroductionWhy should anyone still be interestedin the analog phonograph? The reasonis simple: today's best record playbacksystems sound better than today'sbest CD players. (CD playback isimproving, though maybe not fasterthan turntable, arm, and phono car-tridge developments.) Moreover,many analog record treasures areunavailable on CDs or other availableand anticipated digital music sources.After all, standards to transmit digitalmusic (and video) directly to ourhomes are developing. This will opena vast library of musical selections forour potential enjoyment.

I believe that commercial considera-tions and the limitations of today'sdigital technology will establish digital

transmission standards of even lowerquality than our current CD standards.Unless these standards are dramatical-ly upgraded (in terms of informationcontent), we may never have a sourceof music for our homes that soundsbetter than the phonograph.

Are analog records inherently betterin some sense? Your ears may alreadybe telling you that analog can soundbetter than today's digital. I willprovide quantitative reasons this maybe so.

Qualitative RequirementsThe subtlety of detail in the grooves ofan LP record is astounding. Quiet, yetclearly audible, details (such as thereverberation characteristic of Car-negie Hall) are represented by stylusmotions of less than an ultravioletwavelength (1/100,000,000 of a

meter)-a dimension approaching thesize of a complex organic molecule.This submicroscopic motion may besuperimposed on an orchestralcrescendo involving stylus motionsthousands of times larger. Over thelast ten years, the ability of moderncartridges, arms, and turntables toresolve this ultra-fine detail, particu-larly during loud and complex musicpeaks, continues to improve beyondall expectations.

Ideally, to reproduce the dynamicrange inherent in the groove modula-tion of a fine LP with the least possibledegradation, the background noise

FIGURE 1: Simplilied noise model of phono cartridge and preamplifier.

added to the quietest passages by thecartridge-preamplifier combinationshould be essentially inaudible.Similarly, the cartridge-preamp sys-tem should be able to clearly repro-ducd the loudest sounds on recordwithout distortion, compression, orclipping.

The same should be true of CDplayback. The quietest passagesshould be reproduced without addednoise or distortion of the rnusiccaused by amplitude steps, or sam-pling intervals that are too coarse, orby filter phase shifts and ringing. Theloudest peaks encoded, as for analogrecords, must be reproduced withoutdistortions, compression, or clipping.

DefinitionsFor CD players, dynamic range isessentially the ratio of the loudest pos-sible output signal to the quantizationnoise, i.e., the noise corresponding tothe round-off error of the least signifi-cant bit. For the 16-bit standard CDformat, this is 96dB dynamic range.

To parallel the previous CD defini-tion, I define the dynamic range of aphono cartridge as the ratio of theloudest sound to the backgroundnoise referenced to the preamp outputterminals. Crucial to this definition isunderstanding that there is an inti-mate relationship between the car-tridge and the first preamplifier stage.Each interacts with the other to estab-lish dynamic range; neither the car-tridge nor the preamplifier standalone.

Oddly enough, the preceding defin-ition is not the conventional one,

ABOUT THE AUTHOR

Hon Bauman received his BSEE from Lehigh University.

He is founder and owner of inSound, which produces high-

end audio amps, preamps, and, in partnership withMapleshade Electronics, the Omega Mikro line of digital

and analog interconnect, power, and speaker cables. Ron

also specializes in personal and meteor burst communica-

tion systems design. With his wile Marcia, he is raising his

sons Marcus and Mitchell. His hobbies include music,

beer-making, llying, and restoring old Volvos.

l6 Audio Electronics 4/96

which is simply signal-to-noise ratio(S/N) at some arbitrary cartridge out-put lcvcl wcll bclow thc louclcst.Often, preamplifier noise is character-ized with the input shorted, which, asyou will see, is an incomplete anduseless way to measure preamplifiernoise. This conventional definition ledto the widespread notion that phonodynamic range is only 60-70dB. Iftrue, this means LPs are about25-35d8 more compressed than CDs,an amount of compression so severethat you would notice a real"Muzak"-like loss of dynamic impactin LPs relative to CDs.

In fact, serious listeners find theopposite is true. Using LP and CDissues of the same performance, theyhave carefully and empirically com-pared state-of-the-art (SOA) phonof;ljfback systems to SOA CD players.LP playback is generally consideredeither better or eclual to CDs in macro-dynamic impact. LPs are usually supe-rior in subtle microdynamic shadings.

ExamplesTo help quantify dynamic range forreal phono playback systems, I usethree modestly priced examples: aSurniko Blue Point, a high-outputmoving coil; a Grado MCZ, a fixed coilwith moving magnet; and an OrtofonMC 1091 a very low output movingcoil. Although better-sounding car--tridges are available, I chose theie formodest price and convenience, not tomention that I own one of each.

To estimate the dynamic rangecapability of the vinyl Lp, first estab-lish the cartridges' sensitivity and thelargest signal amplitude it must han-dle. The sensitivity figures in units ofmY /cm/s are: Blue Point, 0.85; MCZ,0.42; and MC 100, 0.018. The worstcase (loudest) recorded sound on arecord in the literature is 105cm/s at7kHz.1

Of these three cartridges, the largestsignal available to the input of thepreamp is 0.85mV/cmls x 105cm/s,or 89mV. This establishes the upperlimit of dynamic range requirea oiinepreamp for the Blue Point cartridge.From a design point of view, the pie-amp should cleanly handle an inputsignal of at least 89mV at ZkHz.

Noise AnalysisCalculating the equivalent preampinput noise is a bit more complicated.The input noise depends on the noiseparameters of the preamplifier and the

equivalent circuit parameters of thecartridge. For the above three car-tridgc.s, thc significarrt cir.ctrit paralnc-ters are the series resistance andinductance. The values are: Blue point2108C1, 190pH;MCZ 70Q, 9mH; andMC 100 34, negligible inductance.

None of the manufacturers states aneed for a loading capacitor. Smallloading capacitors and cable capaci-tance and inductance have a second-order effect on the equivalent electri-cal noise anyway, so I neglected themin the following analysis.

Figure 1 shows a simplified equiva-lent circuit for analyzing the noiseperformance of a phono ca"rtridge andpreamplifier, or pre-preamplifier. Thecircuit model is based on the Rotl-re-Dahlke3 theory of noisy fourpoles (inwhich the preamplifier has one inputport and one output port). In thismodel, amplifier noise originates, ataudio frequencies, as two uncorrelat-ed generators: an ideal noise voltagegenerator, e*, and an ideal noise cur-rent generator, i*. These generatorsinteract with the cartridge impedanceto establish the basic noise level of thephono playback system.

The figure includes a transformer toshow the effects of coupling very lowoutput-moving coil cartridges to pre-amplifiers. You assume the trjns-former is ideal, but you can representits losses by increasing the power ofthe preamplifier noise geneiators. Toapply the diagram to transformerlesspreamplifiers, simply set N, the turnsratio, to one.

To calculate the S/N ratio at thepreamplifier output, first calculate thedesired output signal as follows:

Vo2 --A,2 [e.2/N2] [tZ(Z+ ft)t2] votts2 (1)

where: Vo is the desired output sig-nal in volts;

_ e-a is the open circuit output voltage

of the cartridge in volts;N is the turns ratio of the coupling

transformer;Z is the input impedance of the

amplifier in ohms;Za is the series impedance of the

cartridge, & + jXc, in ohms;

_A, is the voltage gain of the pream-plifier.

The output noise is:

No = [A12lN2] [er2 + N2er2l[tZ(z + z")12+liNztN2lltzczl(z+ 26)t2ll votrsz

- (2)

age of the cartridge resistance in volts;e, is the equivalent input RMS

voltagc noisc gcncrator of the pream-plifier in volts;

i* is the equivalent input RMS cur-rent noise generator of the preamplifi-er in amps.

The output S/N ratio is (1) dividedbv (2):

Vo2/No = ec2l[eR2 + N2er2 + [ir?Nltlz.l2]l(3)

Notice that the input impedance ofthe preamplifier has dropped out,and, therefore, does not direitly affectthe S/N ratio.

Shunt resistances placed across thepreamplifier input increase the noisepower of the voltage and/or currentgenerators. Such resistors can onlydecrease dyrlamic range by increasingnoise. Motchenbacher and Fitchenashow that the output S/N ratio ismaximized if the following is true:

N2[e*/ir]= lZ.l ohms (4)

- Substituting (4) into (3) and simpli-fying yields:

Vo2lNo = eczllen2 + [eri, lZ"l]l (5)

- Assuming optimum noise coupling,the output noise is dependent on theproduct of the basic noise generatorsof the preamplifier and the magnitudeof the cartridge impedance. Equation(5) shows that the preamp,s e*in,parameter is useful for choosing ilow-noise preamplifier; the lor.iere*i*, the greater the potential S/N.

Therefore, consider using e*i* asan appropriate figure for any ampUfy-ing device in which low noise isimportant. I find it more useful thannoise figure because the parametercontains information necessary tonoise-match to a source and comparetwo devices.

Of course, as with noise figure, eri*varies with frequency, bias cur.eiri,temperature, and even signal level.For my calculations, I account forvariations in frequency by breakingthe frequency band into small seglments and assume typical bias cui-rents and temperatures.

Noise MatchingFor a low-output moving coil car-tridge,-the source impedance is verysmall, for example, 3C) resistive for th-eMC 100. For such resistances, it iswhere: eo is the thermal noise volt-

Audio Electronics 4/96 l7

(The gains shown in Tnble 1 are morethan adequate to assure that second-stage noise is negligible.) Figures 3aand 3b summarize the results of thespreadsheet calculations.

LP vs CD Dynamic RangeThe vertical bars in Figs. 3a and 3brepresent the dynamic range obtain-able with various combinations of car-tridges and preamplifier devices. Theline marked with squares representsthe optimum dynamic range attain-able with an ideal noise-matchingtransformer. Ideal means it adds noadditional noise and varies its turnsratio to match the ratio en,/iy as afunction of frequency. Figure 3aarranges the preamps in descendingorder of their e*i* product, while Frg.3b shows the preamps in descendingorder of their noise voltage gener-ators, e*.

For the high-output cartridges, theSumiko Blue Point and the GradoMCZ, the dynamic range possiblewith good low-noise devices, such asthe C413N or AD797, is almost opti-mum. For the low-output moving coilcartridge, the MC 100, the dynamicrange approaches within 3.5dB of opti-mum for a preamp with eight 2N4403transistors in parallel. Most important-Iy, the dynamic range potential of any ofthe three cartridges uith its best preamp isequal to or better than the theoreticalbest aCD can achieae! The best of these mod-est cartridge-preamp combinations has16dB better dynamic range than theCD upper limit.

The best transformerless combina-tion, the Sumiko and eight parallel2N4403s, has greater than 112d8dynamic range, and is only 1.5d8 shyof the optimum combination of aSumiko with a transformer and aC413N FET. At 1l"1dB, the Sumiko/4D797 combination is only 1.7dB lessthan optimum.

In Fig. 3a the trend in optimumdynamic range performance for any ofthe cartridges follows the trend in thee*i* product. Interestingly, the opti-mum dynamic range is very nearlythe same for all of the devices exceptfor the HA5190. This means that car-tridge noise generators tend to domi-nate this set of optimally noise-matched phono preamps.

However, for nonoptimum cases/the trend is not so straightforward.The e./i* ratio interacting with thecartridge impedance determineswhich is the best combination. For

20 Audio Electronics 4/96

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FIGURE 3a: Preamps arranged in descending order of er.i".

example, for the Sumiko and Ortofoncartridges, the parallel combination of2N4403s is best (highest dynamicrange), while the C413N is best for theGrado. The larger impedance of theGrado cartridge favors those preampswith lower i*.

In Fig. 3b, where the data is

arranged in order of descending e*,the dynamic range of the relativelylow-impedance moving coil car-tridges, the Sumiko and Ortofon, fol-lows the trend in e*. The Grado,because of its significantly greaterimpedance, does not always followthe e* trend.

Table 1. Preamp Galn Requlrements for 3 Phono Cartrldqes

Frequencv Maximum Equivalent SUMIKO GRADO OFTOFON(Hz) lnput BLUE POIUT I\4CZ MC 100

Velocitv (cm/sec) lnput to 1st Staoe (Vrms)

7 0.7 6 6.46E-04 3. 1 I E-04 I.37E-0520 0.65 5.53E-04 2.73E-04 1.17E-05

700 26.09 2.22E-02 1 .1 0E-02 4.70E-043 000 80.00 6.80E-02 3.36E-02 1.44E-0370 00 I 05.00 8.93E-02 4.41E-02 1,89E.03

11000 40.00 3.40E-02 1,08E-02 7,20E-04

@(10 Vrms Max Outpul)

112 __ 227 _ tr2sr-lnpu to 2nd St

RIAA Weighting7 1.00 0,07 0,07 0.07

2 1 .00 0.06 0.06 0.0670 0.1 0 0.25 0.25 0.25

3 000 0.10 0.7 6 0.76 0.7 6

7000 0.10 1 .00 1.00 L0011000 0.10 0.38 0.38 0.38

Maxlmum 2nd Stagg._9aln l_0 LO 1010 Vrms Max )utout)

Prea rp Output (VrmsRIAA Weiohtino

1 .00 0.72 0.72 0.7220 1 .00 0.62 0.62 0.62

70c 1 .00 2.48 2.48 2.483000 0.50 3.82 3.82 3.827 000 0.25 2.49 2.49 2.49

11000 0.16 0.62 0.62 0.62

Holman, Tomlinson

---AUDO. tr"|, 1rnequirements ol Ph onographic Preamplr- lers,"

l--

@o

ocGsEco

The bottom line here is that if yourgoal is to achieve best dynamic range/select the preamp and cartridge withknowledge of all the relevant parame-ters. Audio amateurs can do this dur-ing the design phase. Preamplifier,low-output transformer, and cartridgemanufacturers should at least statetheir products' parameters so you canmake intelligent choices. Of course, Iam not suggesting that we choose com-ponents on these parameters alone.

Beyond the NumbersWhen comparing the sound of phonoplayback with digital, note the differ-ence in the way noise combines withthe signal and how humans react tothat noise. Phonograph thermal noiseis linearly added to the signal. Thus,the right kind of filter can retrieve sig-nals below the noise level. Our earsare the right kind of filter. We canretrieve musical signals that are10-30d8 below the thermal noise (or

tape hiss). You can decide if this factoradds an additional 10-30d8 to themaximum dynamic range for LPs Ipreviously calculated.

No doubt, we can more readily hearmusic embedded in thermal noisethan in quantization noise. Why?Digital noise destroys information,whereas thermal noise adds innocu-ous, unrelated information to music.

Ironically, despite the low noiseusually attributed to digital, quieterpassages of records sound better thantheir digital counterparts. The greaterdynamic range potential, and the abili-ty to hear music well below analognoise, and digital's quantization dis-tortion of quiet sound all partlyexplain why I, and perhaps you, stillprefer the best phono playback sys-tems to their digital counterparts.

EpilogueThe intent of this article is to demon-strate that the LP is, contrary to popu-lar belief and the opinion of the audiovanguard press, potentially superior tothe CD in dynamic range. I used a rig-orous, ar-ralytic approach to do this. Itake little comfort in the results of the

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FIGURE 3b: Preamps arranged in descending order of e,u

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I

Audio Electronics 4/96 2l

analysis because numbers rarely tell usmuch about how audio componentssound. In this case they seem to sup-port what I already believe to be true.

The following colnrnents, althougl'rspeculative, support the notion that wehave much to learn about how humansperceive music. An understanding ofthis process will help us to identify thesignificant parameters for audio repro-duction systems and to develop tech-niques for measuring them.

Myth of the Frequency DomainLiterature suggests that perfect play-back is possible if we could onlyreduce measured distortion and noiseto inaudible levels. Up to this point, Ifocused on noise and dynamic range.For the digital case, the term quantiza-tion distortion is more appropriatethan noise, since quantization isessentially a nonlinear process.

We generally consider nonlineardistortion as harmonic and intennod-ulation distortion, which we measurein the frequency domain, and usesinusoids as the test signals. Almostall of our audio equipment is charac-terized in the frequency domain. Yetmodern sensory research suggeststhat our ears are not Fourier analyz-

ers, decomposing music into sinu-soidal cornponents. At least for rnusicour ears seem to be very sensitive,perhaps most sensitive, to distortionsir-r the time domain. We hear livemusic and listen to recorded music inthe time domain; i.e., we process vari-ations in air pressure as a function oftime, and do not receive or perceivemusic in the frequency dornain.

I believe fidelity in the time domainis paramount. Consider that greatorchestra leaders breatl-re life intomusic by controlling the flow of themusic in the time domain, i.e., by mak-ing adjustments in tempi and loud-ness. Not much training is required tohear differences between first- andthird-rate orchestra conductors.

This, of course, doesn't prove mytime-domain hypothesis. It doesunderscore the idea that our hearingmechanisms are highly sensitive inthe time domairr. We can reasonablyassume that similar perceptual mecha-nisms are at play when we perceivethat something is not quite right withtoday's digital music, and that digitalis doing something wrong in the timedomain. We know that major im-provements in digital happen whentime-domain jitter is reduced, but

there is sornething more fundamental-Iy wrong with digital.

The Trouble with CD SoundTo quote from an article by Fonte6: "ltis a mystery to me how basic conceptscan get so twisted around that theybecome nearly meaningless. In thisnew world of digital sampling sys-terns, you would think that tl-reNyquist theorem would be as familiaras Ohm's law Nevertheless, as timepasses, I see more people and publica-tions misunderstand its implications.The results of these misunderstand-ings are circuits that don't work welland designs that arc inappro-priate....Simply stated, tlrc Nyquist tlrc-orent tells yotr tlrc trrirrirrtutrt snntplirtgrnte needed to recortstruct n sigrnl's fre-quetrcy witlrout nl iasing."

The theorem fails to directly men-tion recovering the phase or ampli-tude of the signal. If the sanrpled sig-nal has a sir-rusoidal sl-rape and alsorepeats for several cycles, phase andamplitude errors will decrease tosmall values. However, if the signal tobe digitized is impulsive and does notcontain rnany identical repeats, thensignificant errors in phase and ampli-tude can occur. Errors in the frequen-

A B c D E F G H I J481 Table 2. Sample Calculations lror4he Spreadsheet482 Nolse Analysls of a GRADO MCZ Cartrldge wlth 8 Parallel 2N4403 preamp483 en tn Rc Lc t No Nt Sandwidth Vn Noise en'in444 (volts/Hz)

^ 1/2 (amps/Hz)^1/2 (ohms) (Henries) (Hz) (volts^2/Hz) (volts^2) (Hz) (volts) (watts)485 2.808-10 2.83E-11 70 9.00E-03 37.5 5.17E-18 1-29E-l6 25 1.14E-08 7.9E-21486 2.80E-1 0 2.264E-11 70 9.00E-03 75 3.76E-18 1.88E-16 50 1.37E-08 6.3E-21487 2.80E-10 1.981E-1 1 70 9.00E-03 150 3.1 I E-1 8 3.1 9E-1 6 100 1.79E-08 5.5E-21488 2.80E-10 8.49E-12 70 9.00E-03 300 1.61 E-1 I 3.22E-16 200 1.80E-08 2.4E-2148S 2.80E-1 0 8.49E-12 70 9.00E-03 600 1.67E-18 6.70E-16 400 2.59E-08 2.4E-2149( 2.80E-10 8.49E-12 70 9.008-03 1200 1.928 B t.54E-15 800 3.92E-08 2.4E-21491 2.80E-10 4.245E-12 70 9.00E-03 2400 1.66E B 2.65E-15 1 600 5.'t 5E-08 1.2E-21492 2.80E-10 4.245E-12 70 9.00E-03 4800 2.65E 8 8.498-1 5 3200 9.21E-08 1.2E-2149: 2.80E-l 0 4.245E-12 70 9.00E-03 960 0 6.64E- B 4.25E-14 6400 2.06E-07 1.2E-21491 2.808-1 0 4.245E-12 70 9.00E-03 1 6400 1.68E 7 1.21 E-13 7200 3.48E-07 1.2E-21495 fotal Nt volts^2 1.78E-13 1 9975 4.22E-07496497 rf a GRADO MCZ wlth a C4 3N JFE]49t en Rc Lc Nt Bandwidth Vn Noise en'in49! (Hz) volts^2/Hz) (voltsa2l tHz) (volts) watts)s0( 8.00E-10 3.1 E-l4 70 9-00E-03 37.5 1.80E-18 4.50E-17 25 6.71E-09 2.5E-2i501 8.00E-10 3.1 E-14 70 9.00E-03 75 't.80E- B 9.00E-17 50 9.48E-09 2.5E-2a502 8.00E-10 3.'t E-14 70 9.00E-03 150 1.80E- 8 1.80E-16 100 1.34E-08 2.5E-2350i 8.00E-10 3.1 E-14 70 9.00E-03 300 1.80E- I 3.60E-16 200 1.90E-08 2.5E-2!50( 8.00E-10 3.1 E-14 70 9.00E-03 600 1.80E- I 7.20E-16 400 2.68E-08 2.5E-2a50t 8.008-10 3.1E-14 70 9.00E-03 1 200 1.80E- 8 1.44E-15 80c 3.79E-08 2.5E-2a50t 8.00E-10 3.1E-14 70 9.00E-03 2400 1.80E- B 2.88E-15 1 60C 5.37E-0€ 2.5E-23507 8.00E-10 3.1 E-14 70 9.00E-03 480 0 1.80E- B 5.76E-15 320C 7.59E-0t 2.5E-2350t 8.00E-10 3.1E-14 70 9.00E-03 9600 1.80E- 8 1.1 5E-1 4 640C 1.07E-07 2.5E-2350! 3.1 E-14 70 9.00E-03 1 6400 1.80E-18 1.308-14 720C 1 .1 4 E-07 2-5E-2351 Total Nt volts^2 3.59E-l 4 1 S975 1.90E-07

22 Audio Electronics 4/96

cy domain can also occur for non-repetitive sinusoids.

Fonte shows that time-domainerrors are inversely proportional to thesampling rate and can be quite signifi-cant. He states that CDs can introduceamplitude modulation errors to 307n,amplitude errors of 0.436-1.84d8, andfrequency errors up to 18% into single-cycle events corresponding to the har-monics of instruments. He gives sever-al arguments explaining why the eardoes not hear these aberrations in CDs:

r distorted harmonics are over-whelmed by the strength of the fun-damental;

o the ear cannot hear an error of0.436dB;

r the ear is not sensitive to phaseerrors in music signals;

o music signals, consisting of manyrepetitions of the same waveshape,average out any of these aberrationsto zero.

Wltile' I rcspcct Forrte's analysis, Iclisagree with his assurnption tl'ratCDs sound great, and that the eardoes not hear the rather large errors

he ascribes to the CD samplingprocess. On the contrary, I think Fontehas put his finger on one of the funda-mental problems with CD sound: time(and frequency) domain errors inher-ent in the sampling process.

That notwithstanding, if the timedomain is important, shouldn't we beable to characterize our audio compo-nents in the frequency domain andthen Fourier transform to predict theirbehavior in the time domain?

Another TheoremSuperpositionT is the basis of Fouriertheory; i.e., the theory states that thereis a weighted set (an infinite set in thecase of nonperiodic waveforms) ofsinusoids, which, when linearly addedtogether, can represent complex wave-forms. But superposition only holds inthe case of linear systems. Of course,we know our systems are aery nonlinenr.As suclr, zoe cannot aalidly use Fouriertransforms to relate a chnracterization inotrc donnin to the other.

When I scc music in thc tirncdomain (at tl-re output of an audiocomponent on an oscilloscope), I donot see sinusoids, but rather nonsym-

metrical and strikirrgly impulsive-looking shapes l-righly correlated intime. I suspect that sinusoidally stim-ulated harmonic and intermodulationcharacterizations tell us little aboutwhat we hear in the time domain.

In the absence of test equipment weuse our ears. Stories about the analogversion of a performance soundingbetter than the digital are not unique,for they have been reported repeated-ly in audio publications emphasizinglistening comparisons. Keep in mindthese comparisons are for a digitalplayback system, which should cer-tainly sound better because its fre-quency domain distortion measures90dB below the maximum signal. Incontrast, the cartridge component ofthe analog playback system measuressomewhere between 30-60dB forsinusoidal references. Clearly, fre-quency domain distortion measure-ments are meaningless for predictingwhich audio components will soundbetter than others.

Wc ncccl to rrrrclcrstarrcl irr rrrorcdetail, and perhaps furrdamentally,how humans perceive and enjoymusic. I predict that time-domain

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03ADmeasurements will be crucial and fre_quency domain much less so. Re_search that develops a set of test tech_nlques more closely related to how theear perceives music could well lead torcvolutionary timc-dornairr instrtr_mentation breakthroughs.

All Noise ls Not Created EqualIl *y earlicr quantification, I wentalong with thc common notion that asingle-dimensional parameter that isthe sarne for botlr recording tcclr_niques represents Lp ancl Clinoise.This is wrong for several reasons:

1. Digital quantization noisesounds-and is-completely differentthan analog thermal or record surfacenoise (or analog tape hiss).

2. Within the cliss of analog ,,ther_mal-like" noises of equal powei maiordrfterences exist in how annoyingthey sound.

. 3. There is good reason to believethat not all quantization noises, evenat equal 16 (or n) bit resolution level,are or sound the same; e.g., D/tr s6n_verters using different roundoff algo_rithms sound different.

. .\.expand on these very fundamen_tal differences, note that iandom ana_log noise, uncorrelated with themusic, operates as another signal lin_early_adding to the music ,ig.,ut. asignal with amplitude less tfiu" tn"norse ts preserved and amplified justas accurately as a signal lirger tiranthe noise. Thus, the ear can fllter outweakcr music from noise.

The.effect of digital quantizationl:tt: it entirely different and quitenonlrnear. As signals grow progres_srvety smaller (relative to the riaxi_

Of course, some analog noises arenot "thermal-like,, ancl- are quiteimportant in audio.

..1. Record pops and clicks, cltre todlrt or scratches. The effect of these onrrrusic is uot lincnr ancl acJclitivc.Instead, the effect appears to be a kindof burst distortion, perhaps analogousto slew rate limiting because oithesteep.scratclr edge thc stylus rncets.Clcarly, irr gcncral, bettcr_sourrdinsturntables audibly reduce the annovlrrrg. quality of pops and clicks boihwrth rcspect tcl thc car,s pcrception ofthe intensity of the initial diJtortiontransi.ent and the ringing therca[ter.

2. "Popcorn,, nois-e associated witha number of op amps. Unlike the hissvnoise we find easy to filter musicthrough, "popcorn,, noise increases inpower with lower frequencies andoccurs in fractional second bursts.This adds a gravelly, grungy sciund,particularly at Iow frequenciii.

3. "Contact,, noise iypically associ_ated with dirty contacti and poor con_nections, or sometimes associatedwitl'r stranded wire in the signal path.This nonlinear noise imparti a digitalc.haracter to analog sound o. .r,Jk",orgrtal sound even drier and moreetched. Others hypothesize that ih;nonllnear elfect on music is the resultof partially shorted point_contactdrodes at the junction between dissim_rlar material.r,.".q., copper and copperoxrde or nickel and nickel oxiie.These diodes are highly

"o"ti.,"u,components which severely distortlow-level music. Distorted iow_levelmusical details submersed withinmore faithful high-level music give"contact" noise a digital character."

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mum signal level the A/D convertercan handle), fewer quantizing bits areavallable to resolve them and smallersignals thus become proqressivelvTof:.dit-!o'!gd by the A/o!ro."rr. ilimit is finally reached wh&e sisnalssmaller than the smallest quuntirltionstep are completely lost.

The A/D p.o."s, sets all such sis_nals.to

3 fixg{ amplitude. There is n"omusrc srgnal for the ear to filter out ofthe quantization noise. I believe thefacts that the ear filters weak musicfrom noise and smaller amplituae sif_

l3lt,1*plily just as u..,r.ut"ly u, nif"are lmportant advantages of analJsover digital. (Some of this advantaeEcan be lost where Class B o, sturuJiAB analog amplifiers, ,rr"h u, *uny

Noisy LPsScrakhed or dirty records are noisy. Agood record vacuuming system ereat_ly reduces rhis noise. SOe .u.triJe;r,arms, and turntables also reduce, b"v asurprising degree, the audibility'ofdirt and scratch effects. However,even a pristine Lp can still emit hissfrom the master tape and,/or recordsurface noise.

. Tape hiss can be largely eliminatedby noise reduction prolessing (at thegxpense of a small loss in"overallfidelity).or by_recording at higher lcv_els (at the risk of compressing Ioudtransients). At least 1OdE of hiss"reduc_tionis possible with either technique.

When audible surface noise occurs,it is due to indifference on the pu.t oithe recording industry-poor_quality

op amps/ are used because they dis_tort smaller signals.)

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vinyl or poor-quality stampers at thepressing plant. Lack of quality controlis abetted by the RIAA record indus-try standard permitting surface noiseof 55dB below a lkHz sinusoidrecorded at 7 cm / s (interpolating fromthc Maximunr Ilquivalcnt InputVelocity column of Table 1, the equiva-lent RIAA dynamic range is roughly67dB at lkHz).

The above notwithstanding, clean,unscratched, good quality recordsplayed back through "first-rate" mod-ern cartridges, arms, and turntablessound as quiet as CDs to me. Moreimportantly, I find well-recorded LPsmore dimensional, truer to the tonalqualities and dynamics of live music,and very noticeably more relaxingthan CDs, particularly during long lis-tening sessions. Additionally, ^yguests, most of whom are not audio-philes, listen to the same source mater-ial played back from LP and CD, andprefer the analog version withoutexception, much to their great sur-prise!

ObservationsI have shown that the phono playbacksystem is capable of greater dynamicrange than 16-bit digital. I am assum-ing that, with proper design and care,the recording process (at least thedirect-to-disc method) should easilyachieve greater dynamic range thanthe playback system. Whether analogtape recording, which is the source ofmost of our LPs and some of our bestCDs, can achieve greater dynamicrange than CDs or LPs needs to beevaluated using the methods of thisarticle.

Fortunately, there seems to be a

ACKNOWTEDGMENT

Thanks to Dr. Piene M. Sprey for many helpful suggestionson organizing the manuscript.

REFERENCES

1. T. Holman, "Dynamic Bange Requirements ofPhonographic Preamplifiers,",4udb (July 1977).

2. Data provided by Mr. Matthews at Sumiko.

3, H. Rothe and W. Dahlke, 'Theory of Noisy Fourpoles,"Pru. I RE M, 8811-818 (June 1 956).

4. C.D. Motchenbacher and F.C, Fitchen, Low NoiseElectnnic Design (John Wiley, 1973).

5. "Audio Handbook,' National Semiconductor Corp.(1976\:2-27.

6. G.C.A. Fonte, "Apply fundamentals to avoid surpriseswith umpled systems," EDN(June 24, 1993),

7. S. Slein and J.J. Jones, Modern ConmunicationPnnclples (McGraw-Hill, 1 967).

rc'kindled consumer ir-rterest in vinyl. Ihope that if this trend continues, andaffordable analog records becomeavailable again, the recording indus-try will produce a quality record, freeof surface noise and warps, thatcxploits the fLrll dynarnic rangc potcn-tial of the phonograph. (We knowmuch bad vinyl was produced, espe-cially near the end of the LP era,somewhere in the '80s, when itseemed that overnight all vinyl hadbeen yanked out of record stores andreplaced by CDs and cassettes. Duringthis period, I remember trying four ormore warped records until I foundone that played. Consumers with sim-ilar experiences must have beenhuppy to see vinyl go away.)

Having said few nice things aboutdigital in this article, I must point outthat I have great expectations. I preferthe convenience and ruggedness ofCDs, and hope that over time theirquality achieves or surpasses analog. Ifind it ironic that with all the technol-ogy advances over the past 40 years,analog tape recorders and records ofthe fifties can achieve a higher stan-dard of musical fidelity than today'stechnology.

But we understand a good dealmore about CDs' limitations, andtechnology has advanced since the 16-bit / 4lkHz standard was established.Affordable 20-bit A/D and D/A tech-nology is here. Those few rvho haveheard 20-bit digital attest to a soundcloser to analog masters (if alsoplayed back at 20 bits).

To achieve analog quality, however,digital standards need raising to per-haps 21 or.more bits. Also, samplingrates must be significantly raised.(The CD standard sampling rate ofjust over twice the highest frequencyhumans are reputed to be able to hear(i.e., 20kHz) is suspect. A growingbody of evidence suggests we canhear rates of change in time-domainsignals that are greater than equiva-lent slopes for 20kHz sine waves.)Most importantly, the sampling rateand quantization levels should matchour ears' demand for fidelity in thetime domain.

Sooner or later the 16-bit/41kHzstandard will be revisited, if for noother reason than to produce a smallbut truly state-of-the-art musicsubindustry. I hope the next digitalstandard is carefully and deliberatelyset much higher than our de factoanalog standard of40 years ago. I

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