Aphex - Compellor.pdf

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AUCProvides computer controlled dynamics for smooth undetectlble c

Presenting the COMPELLOR, a revolutionary audio processor. It delivers intelligent compression, leveling, andpeak limiting simultaneously! The COMPELLOR control circuits include analog computers that constantly analyzethe input signal, varying complex control characterisitics sent to a single VCA per channel. Operating controls arethus kept to a minimum, for the COMPELLOR intelligently vanes ail the parameters foryou. Ail you need do is setinput level to control the amount of processing, adjust output level and set the balance between compressionand leveling. That's it. The COMPELLOR will then provide complete dynamic control — smooth, inaudiblecompression, increased loudness, freedom from constant gain riding, and the desired density- ail automaticallyits unique circuitry actually enhances transient qualities, making even heavy processing undetectable.

This smart, versatile, cost effective processor is equally at home in broadcast pre-processing, microphonecontrol audio recording and production, tape duplicating, live sound and film dubbing; producing the "sound"audio engineers have always sought but seldom found.

The COMPELLOR's simple audio path is compnsec of .a differential>nuutner.[at,cn input stage, the world renown Aphex 153 7 A VCA.and a new. electronically balanced. Transformerless output stagewhich can be used balanced or srrg.e-r^oed The nominal operatingievel of cne COMPELLOR {and OVU on [he meter) :s 'Pter.nailyjumper selectable at -10. 0. -4. and -8cBm co m^tch any system

There are three mam detector circuits for compression, leveling,and peak limiting.

LEVELING !s performed in a manner re'ared to the way the <?arperceives ioudness ever long time .ntervais The circuit maintainsoutput level witnmldB for a 20CB input ievel change The action isslow enough io have minimal effect on program transients or shortterm dynamics

When leveling and compression are used together, the ieveiermaintains [he gam platform so that compression is consistent overvarying levels of material, providing a uniquely smooth soundingdynamic compression.

The leveling action is interactive between the two channels,preserving overall balance and stereo imaging.

COMPRESSION rs also accompnsnpd ever a 20dB range of .rputlevels ^'ir me ratio varying from 1 i > :c 20 > "he arrac* and 'eieasetimes delved from and varying -A!th. the program ^ate-'ia! This" \ct <^ee" heips ro prevent the "choked" -:CL'"'.1 ,JSi_.ai'v associatedA'lth deeo compression Further program dependent characteristicsare •mparted by other sections of the COMPELLOR's computer, ;heQY\'AM'C VERIFICATION GATE j'DVG! ana the DYNAMICRECOVERY COMPUTER (DRCI

The DVG monitors short term and :-c-rQ :erm ,^verage 'evels.comcares [^em and impedes gam changes •,vnen program dvnam.esmight De '.ac''ficed for arbitrary gasp -eduction The DVG alsoprevents gam release during short term orcgram pauses whichother-wise wouid cause "pumping" a "creachmg" effeas Vocafmater:ai is especially benefited by mis 'earure sounding naturaleven Ahen extremely compressed DVG action is indicated by afront cane' LED

The DRC aliows very rapid recover/ from gain reductionunder certain complex wave conditions Signals that sre high -npeak amplitude but low m relative power can cause an increase inthe compression release rate Unrequired gam reduction is thus inhibited.

oreventing loss oftransient vvavefrcnts, holes etc The some ben*r?'r•s substantial, contributing toward natural, open sound, even when"ighiy compressed

The PEAK L3MJTER provides furtner dynamic control hcldinc srabsclute ceilmg !2dB above the nominal fOVUj ie-yef Alrhougnextremely fast, this unique iimiter is virtually inaudible <.n ,15..operation

Tr<e SILENCE GATE detects significant gaps >n program materialand freeze:; :he processing, preventing noise "swefl" or Duiidupcommon tn other AGC devices, then .nstanty releases when proof^rnresumes

The STEREO ENHANCE feature does just that. By detecting andrnatnxing certain stereo information and sending ;t to the sidecha*ns.STEREO ENHANCE creates a subtle naiural widening of the stereo-mage that ;S 'uiiy mono compatible It is not a "stereo synthesizer"and it has no effect on mono or center channel matenal

COMPELLOR.™ Dynamic Verification Gate,rw and Dynamic RecoveryComputer.™3re trademarks of Aphex Systems Ltd

) COMFRESSOR/LEVELER/PEAK LIMITER>resslon, increased loudness, and Intelligent automatic gain-riding.

from APHOC SVST0HS LTD.Unique * Revolutionary • Cost effective

APPLICATIONSBROADCASTING (as a pre-process'-na too!)

In the race for lourfness it is qua:iTv which usually suffers Whenrequired to work too hard ever trie best multi-band processordegrade the aud.o By pre-conajt'onmg the signa; w;th theCOMPELIOR the following processor is fed a s<gna' with anoptimized dynamic range, thus avowing it to be ope;a'ec* in i;s"sweet spot" without concern iy possible overload Since theCOMPELLOR does no; degrade t-e audio the total result win becleaner sound, with equal or greare' apparent loudness

A different problem faces classical stations, especially with thenewly expanded dynamic range of o-gital audio The quieter passagesget "lost" m the ambient noise floor, which may. m a movingautomobile, be highe' by more tnsn 30dB The COMPELLOR can"lift" these passages without charging dynamic and transient feel,thereby pleasing the audiophite and the computer alike

Another benefit of having rhe COMPELLOP in [he broadcastchain is that fader settings on the console become less cniicaf Thesound of the station will nor change from the DJ who loves thesound of the meters pegging to the~DJ who is afraid to make themmove

Television broadcaster a?e ofr.e'"' faced witn the proDiem of p.large d;"eren-ce o' apparent Iouo"<es5 between program materialana commercial With a COMP=LLOR the apparent loudness ofme program car be <nrc-ased vi^ie already hesvtl> compressed

commercials go through without tunhe; p'ocess '̂Q Thene; 'esul: isconsistent appa^nt ie^ls from program to prograr a^c fromprog-am to commercial

PRODUCTIONThe one drawback (if i; can be caned ihatt of the CQM^EilDP >s

tha; it is almost impossible to ge; an "effect" o<" colora:-cir"" CJ' of;:So i? ;he goa' <s simply to nave dean uncoiored level con'ro1 c-r* snyparncu:ar track the COMPELLOR IS pe^ec As men:ionec ••: ispart'Cuiafi'y natural sounding on v-ocals Drums and bass a'so soundgreat processed by the COMpEl.LOR though they wouia no'maiiyrequire different settings than for voice O' course the CGVFELLORIS excellent fo' processing a totaf mis to maintain max.mumconsistency and loudness (e g maste^ng!

SOUND REINFORCEMENTFeedback is one of the biggest problems m live sound Jus; when

the fader on a voca1 input is set the vocalist starts to smgiouaer TheCOMPELLOR. however, can maintain maximum leve! beforefeedback

The COMPELLOR also shines in conuoiifng multiple sou'ees ofdifferent leve*s. such as conferences The speakers will a!1 beea^a! inaoproximate ioudness without chanamg the chara::ef o' eacninoiV'!auars ^o;ce

Paging systems can sound louder anc clearer vviihoj; ar»> over-load a-stor-ion and without increasing amp '̂i-cat'On

STL/PHONE LINE DRfVERMaintaining consistent dnve le-^ls v^hiie controlling peaks (without

overshoo: and ringing! is JUSt another way of describing [heCOMPELLOR Full modulation of the STL can be sustained withoutconcern fo< overload Audio level will be kep' wel! above the noisefloor of phone lines or STL. again without crashing anything followingthe COMPELLORCARTING/TAPE DUPLICATION

Different audio levels from cart toca^t is an aH too Typical problemWith the COMPELLOR. levels can be easily maintained to assuremaximum signal to noise performance without tape saturation TneCOMPELLOR rs especially useful in assembling tapes from severalsources with varying levels onto a single tapeMIC PROCESSING

One of the most difficult signals a processor encounters is thehuman voice The COMPELLOR works beautifully on voice byproducing a dense, "punchy" sound while retaining dynamic andtransient qualities The apparent level will be consistent withoutchanging the urgency and exatrnent of a screaming DJ or alteringthe intimacy of a soft-spoken female voiceFILM DUBBING

Matching levels between multiple sources and within a singlesource is often a jot) which requires more than one persor to ndegam anc1 switch sources at the appfopnare nmes Thf-COM Ft Li. OPmakes the job much simpler ii is especially effective o n oosca;sound tracks which are so sensitive ro any peak overload

SPECIFICATIONSINPUTType »RF-filtered true instrumentation differential

balancedInput Impedance • 50K Ohms balancedNominal operating level • user selectable

OVU=-10. 0, +4, +8dBmMax input level • +27dBmCMRR • greater than 40 dB

SIDE CHAINCompressionAttack time »5-50m Sec jRelease time • 200m Sec-] Sec I Program dependentRatio •1.1:1-20:1 IThreshold • 30 dB below nominal level (OVU)

with input full clockwiseLevelingAttack time • 2.5 Sec jRelease time • 5 sec \ Program dependentRate».5-5dB/Sec IThreshold • same as CompressionPeak LimiterAttack time • iji.SecRelease time • 10m SecThreshold »l2dB above nominal level (OVLJ)

Gain reduction element • APHEX1537A VoltageControlled Attenuator

OUTPUTType • Electronically balanced transformerless.May be operated balanced or single-ended at

full output.Source impedance «20 ohm balanced, 10 ohmunbalanced.Maximum output • +27 dBm balanced or +21 dBmunbalanced.Band width • +1 dB 5HZ-65kHZHum and noise @ unity gam, +4op level • -72dBmNoise referred to max output • - 95dBmDynamic THD @ 20dB compression, 1 KHZ, +4 op

level •.!% max

SIZE • 13/4" H x 19" W x 9" DSHIPPINGWEIGHT.il lbsPOWER REQUIREMENTS • 90-250 VAC. 50-60HZ,20W

AC input is IEC standard receptacle, with fuse,voltage select & RF filter.

APH€X SVSTGTtS LTD.13340 Saticoy St. - North Hollywood, California 91605 - (818) 765-2212 - TWX: 910-321-5762

studio soundAND BROADCAST ENGINEERING

he APHEX

COMPGLLOR TM

This article (or set of articles) is a somewhat unusualdeparture for us, as it represents neither an objectiveor subjective review, prepared by our own reviewers,nor is it the normal type of article we ask amanufacturer to write, providing an insight into aproduct: it is somewhere in between. Aphex workedclosely with a number of top industry names duringthe period before the Compellor was released, and

ensured that it received a good deal of field testing.Aphex asked some of their users (some who had seenthe Compellor at the prototype stage, and others whohad not) to write down their comments andexperiences with the unit for us to publish. At the veryleast they represent a useful insight into theapplications and operation of what appears to be aunique and highly useful dynamic control system.

Barry Victor, radio stationKROQ-FM, director of technicaloperations. Previously chiefengineer, radio station KMET.Technician, technical servicesCBS Television, KNXT & CBSTV CITY. Asst productiondirector, Drake Chenault EntInc.

Areas that can benefit by using gainreduction are:(1) Main programme channel(s)

before studio transmitter links;(2) Microphone pre-processing

(levelling);(3) Production studio levelling

(tape headroom).Main programme channels that

are before the STL (studiotransmitter) link need to have thelevels kept within certain parametersto protect the STL from being

overdriven so as not to causedistortion and also not to be too lowin average level so as to maximisesignal to noise ratio of the STL.-Most radio stations are run in a"combo" operation where the discjockey controls the audio levels aswell as produces and announces theshow. As most DJs are not tech-nically inclined, levels from an on airconsole can range from - 20 dB to+ 20 dB. An automatic gain controldevice or AGC is employed tocorrect for the wide discrepancies inlevel.

Microphone pre-processing is verydesirable at many times due to thewide dynamic range of human voice.Again, as DJs are more concernedwith the programming aspect oftheir shows, a compressor on the micchannel can be very helpful forkeeping levels constant and theprogramming intelligible. When

interviewing guests mic levels can bekept from causing undesirable feed-back on open mics from headphonesby a noise gate.

Production studio levelling canprevent audio tape from oversaturation causing distortion. Againair talent producing commercialspots are more concerned with theend produce than with technicalconcerns. Audio tape headroom canbe extended by employing a peaklimiter to prevent unwanted tran-sients from saturating the tape. AnAGC unit can be used to provide aconsistent level to maximise signal tonoise during recording.

Up until the early 70's the mostprevalent AGC unit was theAudimax and its companion limiter,the Volumax. These units and themany others of their type were quitegood for their day. In fact you canstill find many of them around in

use. The main problem with thistype of limiter and compressor isthat they can cause pumping orbring up a lot of background hissduring quiet passages when used toexcess. Peak limiters like the UREILA-2 and the later model 1176 havebeen used to protect sources fromtransients but they can causepumping when used to control morethan peaks.

There is then the problem of FMbroadcasting in which you have a75 ^s pre-emphasis curve toovercome signal to noise problems inthe transmission. This brought outproducts like the FM Volumaxwhich inserted a 75 ^s pre-emphasiscurve in front of the limiter to causethe high frequency information tocreate more limiting so as not toovermodulate the transmitter with*high frequency peaks. This works

STUDIO SOUND, MARCH 1984 REPRINTED WITH PERMISSION

Aphex Compellorfine when you don't have to have a"loud", competitive sound.

This was partly solved in theintroduction of two types of peaklimiters/lesellers. The three-bandDAP-310 and similar units whichallowed individual compression/limiting of three separate audiobands helped in being able to limitthe high frequencies without causingunnatural-iounding loss of lowfrequencies. The other was Optimod8000 whicii took a 2-band limitercompressor and matched it with astereo generator. This allowed closerattention to prevention of over-shoots and peaks which cause un-wanted over-modulation products.

A large problem with audio gainreduction products is that some cancause rafter large amounts ofharmonic distortion when they areoperating. Some have built in over-shoot problems due to faulty trans-former designs or large amounts ofIM distortion products caused byphase shifts or similar problems.Some multi-band processors willcause phase shift, ringing anddistortion due to the splitting of thefrequencies by very sharp filternetworks and then the resummingnetwork which can cause cancella-tions in the. audio source.

The problem with overshoot anddistortion products in the broadcastfacility is that these products tend toovermodutate the broadcast trans-mitter causing the station to have tolower its average levei of modulationto compensate for them. Of coursedistortion is not pleasant to listen toand will cause the listener to fatigueand possibiy tune out.

Lately with the introduction ofsuperior audio performance stereogenerators, FM exciters and newhigh performance STL microwaveradio, the gain reduction units showup as the weak link in the broadcastchain.

Long a problem in many US radiomarkets is the need to be as " loud"as or "louder" than the competi-tion. This involves a large trade off,one of apparent loudness and that ofaudio quality. The reason behindthis is thai you only can modulate somuch before you exceed set stan-dards and risk being fined by theFCC. Several means have beendeveloped to allow maximum modu-

TABLE 1All measurements made with 0 dB reference at + 4 d8V.Output control full clockwise. Input adjusted to achieve output level.Stereo enhance circuit out.All tests performed with Sound Technology 1710A.

Frequency responseProcess control at full compress 10 dB gain reduction

10Hzto20kHz -0.0+1.0 dB50 kHz +13.0dB

Process control at full levelling 10 dB gain reduction10 Hz to 20 kHz -0.0 +1.0dB50 kHz +13.0dB

Tota! Harmonic Distortion

Process control at full compress 10 dB gain reduction700 Hz 0.065% with 30 kHz bardpass700 Hz 0.087% with 80 kHz bandpass700 Hz 0.097%10 kHz 0.070%10 kHz 0.090%

with no filterswith 80 kHz bandpasswith no filters

Process control at full levelling 10 dB gain reduction700 Hz 0.055% with 30 kHz bardpass700 Hz 0.070% with 80 kHz bandpass700 Hz 0.090% with no filters10 kHz 0.060% with 80 kHz bandpass10 kHz 0.080% with no filters

Clip level at 700 Hz + 20.0 dB + 24.0 dBV

Noise floor 700 Hz tone at reference silence gate engaged-65.5dB -61.5 dBV

Absolute noise floor. Output control full clockwise iisput shorted-74.0dB -70.0 dBV

Smpte—IM distortion4:1 Ratio

Process control full compress 5 dB gain reduction0.056%

Process control full levelling 5 dB gain reduction0.25%

lation of audio programming—eglarge amounts of compression tokeep the average level at its highestpossible level and then to useclipping to keep the peaks from overmodulating. There are severalclippers in various final limiters andseveral clipper products made to beinserted after the stereo generator toprevent overmodulation and tomaximize the average loudness. Theproblems with these, of course, areif you use them to excess you make avery hard sound, one that can tirethe listener out. Face it, squarewaves are not pleasant to listen to.So the engineer has a fine line totread to have a signal that is loudenough to cover the intended areaand please the programme director(who wants to keep a competitiveedge of loudness) while still trying to

maintain a quality signal that won'ttire the listener, or worse yet drivehim or her away completely.

I was made aware of a possiblenew product from Aphex Systemscalled the CompelJor some time ago.I was invited M see and hear aprototype and asked for my ideas.The product sounded very good andI offered the suggestion that it bemade with minimum of user controlsand the cleanest audio path. Trans-formerless balaaced floating inputstages were designed so that it couldbe used in any environment with anytype of equipment and not have sideeffects of transformers.

The Compellor can be used singleended. Either leg of the input or the3 pin XLR connector can begrounded and ao change of leveloccurs as compared to normal

balanced output. Input and outputcan be 0 dB referenced at +8 , + 4 ,0, or - 1 0 dB. The heart of theCompellor is the DVG and the DRCwhich control the attack, release andlength of compression or levellingdepending on where the process mixpot is set. Either full compression orfull levelling or any mix in between ispossible. The actual attenuator is theAphex VCA which offers excellentperformance. Refer to table 1 foractual measured performance.

The Compellor also has a built infast peak limiter riding 12 dB abovethe 0 reference, it prevents transientsabove 12 dB from passing.

Referring to Fig 1 we have a1 kHz square wave at 22 Vamplitude. Top trace is input toCompellor, bottom trace is output.Both traces are vertical 10 V/div,the horizontal is 500 /js/div and theexpanded horizontal is 20 /js/div.T*he Compellor is set for 10 dB gainreduction. As you can see the inputand output traces are almost identi-cal showing no ringing or overshoot.

Fig 2 is a 100 Hz square wave at22 V amplitude. The top trace is theinput to the Compellor, the bottomis the output of the Compellor. Bothtraces are vertical 10 V/div the hori-zontal is 2 ms/div. The Compellor isagain doing 10 dB gain reduction.The picture shows very little tilt ofthe low frequency components andno ringing or overshoot whatsoever.

Fig 3 is a 10 kHz square wave withinput of 22 V amplitude and outputof 13 V amplitude. The Compellorseems to think of a square wave ofthis frequency a little harder as thegain reduction settled in at 20 dB.The top trace is the input at10 V/div and the bottom trace is theoutput of the Compellor at 2 V/div.Horizontal was 50 jjs/div and theexpanded was 5 jis/div. This showsa very slight rounding of the edge ofthe output but once again no ringingand no overshoot.

As evident by these square waveresponse pictures the Compellor is avery transparent device exhibiting noreal degradation to the audio source.

Due to the Compellor'% uniquecontrol circuit a stereo enhancementcircuit can be derived from controlvoltage only to cause the compressorto increase the apparent separationof the two channels enabling anincrease of the stereo effect. Thiscomes in real handy as in conven-

STUDIO SOUND. MARCH 1984

tional compression, the more com-pression that is done the lessapparent the stereo effect is. The

•e- silence gate will freeze the level ofthe Compellor when audio drops toa predetermined point to avoidincreasing background noise. Alsoyou can see the silence gate detectordoes not control the audio directly.It controls the sidechain whichinstructs the VCA thereby giving avery clean yet stable command.

I was finally able to get one of thefirst Compellon off the assemblyline and actually try it out. The unitwas bench tested with the results inTable I, and was put into service ashort time later. The Compellor wasput into the broadcast chain at thestudio just before the STL. Depend-ing on the programme material andwho was running the air console thegain reduction was anywhere from5 dB to around 18 dB. the Com-pellor was able to handle this withno problem and the silence gatemade times of low or no modulationvery quiet with no hint of pumpingor apparent squashing effect asevidenced by other compressors, iwas able to let my final limker at thetransmitter do barely any work at allexcept for high frequency protectiondue to the 75 JJS pre-emphasis.

One of the next two units wentinto the production room to beinserted between the productionconsole and the input of the taperecorders. The Compellor has aidedour production team in the produc-tion of taped spots and especially inthe caning of music. We put a fewsongs on cart that are hard so find oronly one copy is available due tolimited release and the differencebetween playing from can or fromdisc can be quite a problem from aquality standpoint. The Compellorwas able to help cut a hotter tapewithout tape saturation.

The third unit was put in the micchannels for two of our on airmicrophones in the air studio. Theyinterfaced very easily and have madea major difference in the soundquality of our announcers.

As a final note the Compellor willwork very well as a pre-!imiter forany final broadcast limiter on themarket and able to provide a punch-ier sound with excellent clarity andnew dimensions of openness. TheCompellor operates with an intelli-gence depending on the musiccontent, ie If the source doesn't needprocessing the Compellor doesn'tprocess. The best thing I can sayabout the Compellor is that youcan't hear it work.

using limiting on vocals; 1) The'squashed' dull sound, 2) The pump-ing effect, and 3) The accentuatedsibilance. Using the Compellor,however, none of these undesirableeffects were noticed even withextreme settings, ie greater than20 dB of gain reduction. I found ithard to believe that I was using thatmuch gain reduction and had to flipit in and out of by-pass to make surethat it was indeed in circuit.

Prior to receiving the Compellor,I was mixing cuts on the newCoyotes album. On one cut I wasconfronted by a female's breathy,soft vocal which was at the sametime, very peaky. The music trackswere heavier Rock & Roll. Usinganother device the peaks weresquashed, words dropped out, thesibilance came up necessitating theuse of a de-esser, and then EQ hadto be used to correct for the de-esser.1 worked like hell to make the vocalsit in the track and was reallyfrustrated when the record companywanted a re-mix.

By that time I had installed theCompellor. I sat down at the consoleand by the end of the first verse 1knew my job would be much, mucheasier.

On another cut off the samealbum I had a problem with the bassnot 'sitting' in the track. I tried every'compressor/limiter in the room (12different types from old to new) butI could not get what 1 wanted. WhenI used the Compellor with approxi-mately 14 dB of gain reduction thebass was even, sitting where Iwanted to put it, and free from anycolouration.

During a recent recording sessionfor Cindy Landis, the signal chainconsisted of microphone, pre-amp,fader, Compellor, to tape. Before Ihad the Compellor, I always had toEQ her voice. Even with the Com-pellor I am sure that I will have touse the EQ to record many tracks,but it does give me greater oppor-tunity to eliminate a stage in therecording process.

I should say that I use compres-sors and limiters as creative devicesin that each has its own "sound".For example, acoustic guitars gainsustain and vitality with compres-sion. The Compellor does not dothis. Simply put, if you are lookingfor level correction without any-other sonic effect, the Compellor isthe only device I know that does thejob.

David J. Holman—independentproducer/engineer. Engineeringcredits include platinum albumsby Olivia Newton-John, Greaseand Xanadu (albums andmovies). Producing creditsinclude Cindy Landis (Alle-giance), Coyotes (Lorimar), KingBees, Mary MacGregor (RSO/Polygram).

Joe Klein — producer/engineerL.A. Trax 1982 Winner of Clioaward, three Internationa!Broadcast awards, sixteen Clioaward finalist. Produced over500 commercials since 1976 forthe top acts for major labelsincluding Donna Summer,Kenny Rogers, Fleetwood Mac,The Doobie Brothers, DavidBowie, Sheena Easton andLionel Ritchie.

I find three main problems whenA record commercial is the onlycommercial except for a movie or a

TV trailer in which the listener orviewer gets a sample of what is beingsold. My job is to make a recordsound bigger than life plus get a salesmessage across all within a span of10 to 60 seconds. Some might thinkthat my mixes are simple in that Itypically have only three tracks—stereo programme and an announ-cer—and sometimes two or threemore for sound effects. Given that Ihave as little as 10 seconds to achievemaximum impact; every milli-second, each nuance is important tome. The success I have had is due tothe attention I pay to detail. Onevery important detail is dynamicrange control.

I make commercials which play onradio (AM and FM) and TV. Everybroadcaster uses some form ofcompression/limiting. If I were tosend out tapes with levels all over theplace, there would be no way topredict what effects the stations'processing would have. In order toavoid, or at least minimize, changesat the broadcast stage my spots allhave tightly controlled dynamics.Aside from level and peak control Iuse compressor/limiters for another,perhaps not so obvious, reason.

1 was always a radio freak. Moreoften than not records soundedbetter to me played on the radio thanon a stereo. These records appar-ently made the broadcast processors"pump" in such a way that thesound was actually enhanced. 1 setthe attack and release of thecompressors so that the pumpinggives a more rhythmic feel to themusic as well as the announcer. Thistechnique is especially effective forR&B spots.

1 use the UREI 1178, and when Iwant a less noticeable effect, I useeither the dbx 165 or the Orban 424.I get the effects that I want withthese devices, but ttsey all haveshortcomings.

1 should qualify what I am goingto say next because I have had theCompellor for a relatively shorttime, but 1 am impressed enough tobe writing this report.

The Compellor does not have theshortcomings of the other devices inthat it has no 'effect'. It makes aspot sound as though I had recordedand mixed very well, instead ofrecorded and mixed and then raneverything through a compressor.That is an amazing thing for me.

The combination of levelling andcompression is a new experience forme. Although there have been othertypes of levelling devices, I felt thatthey degraded the signal too much tobe of any use. The Compellor,without colouration, smoothes outmy mixes making them easier and, atthe same time, better.

I recently completed the wintercampaign for ON-TV (subscriptionTV). Since this was all dialogue, Idefinitely did not want any of thecompression 'effects' I mentionedbefore. I needed clear, clean, punchytracks. I found that using the Com-pellor, even with over 14 dB of gainreduction, clarity was not lost.

After the Compellor, I used the

Aphex II Studio Exciter. This gavethe tracks even greater intelligibilityand punch. The Aural Exciter is avery important part of my sound,there is nothing that I have producedin almost 3 years which did not runthrough the unit. The combinationof the Compellor and the AuralExciter is powerful—a consistent,tight mix with a very dynamic feel.

Another spot I 'Compelled' wasfor Kenny Rogers "Greatest Hits"LP. The problem in that one was Ihad to connect 10 songs, each with adifferent texture, together with anannouncer. The Compellor smooth-ed the transitions beautifully.

A client typically does not knowwhat equipment was used, norshould he care. When I delivered thenew spots to ON-TV, the responsewas "God, that sounds fantastic".That is, for me, the bottom line.

Frank Kejmar—manager/Recor-ding Services/MCA/WhitneyStudio Engineering for over 20years. Credits include platinumalbums for Barry White andAretha Franklin, audio forHanna-Barbera animation andDisneyland exhibit "AmericaSings".

I used the Compellor on themixdown of the opera Bells ofBethlehem. The orchestra had beenalready mixed in London, the sixsoloists were recorded with AKGC12, and the twenty-five voicechorus was recorded with overheadAKG C24 mics in stereo-M/S.

With pop music you can get awaywith using a variety of limiters.Classical dynamics, however, aremuch more varied and critical. I hadat least 20 dB of dynamic changes inthis project and only the Compellorkept the levels inaudibly controlled.

The vocalists thus appeared tohave excellent mic technique withoutany conscious effort on their part.Chances are I could have achievedthe same results by riding the gainmanually for five or six takes, butthe Compellor did it perfectly thefirst time. Another way of achievingthe effect would be to program levelchanges via automation, but thatwould be time wasted if you have aCompellor available.

One does have to recognise thathigh level and low level balances willchange depending on the amount ofprocessing. The already mixedorchestral track was fine for thealbum master. I had to make aspecial mix for cassette duplicationwhich was going to be played backduring live performances. I wantedto avoid any need for gain ridingduring a performance so 1 ran theorchestra mix through the Com-pellor. Again, it did the job withoutany colouration.

The Compellor is very simple touse, after five minutes of playingwith it, I had complete confidence inits function. The metering wasuseful in that I had a good indicationof what the unit was doing dynam-ically at any particular time. •

SHORT FORM CATALOGUE

INNOVATIVE PRODUCTS FROM APHEX.FOR SUPERIOR SOUND REPRODUCTION

COMPELLOR" COMPRESSOR/LEVELER/PEAK LIM1TER

Presenting the COMPELLOR'," a revolutionaryaudio processor. It delivers intelligent com-pression, leveling, peak limiting simultaneously!The COMPELLOR" control circuits are actuallyanalog computers that constantly monitor theinput, adapt and control a single VCA perchannel for minimal signal path. Operating

THE APHEX AURAL EXCITER"

controls are kept to a minimum, for theCOMPELLOR" intelligently varies all the para-meters for you. All you need do is set inputlevel to control the amount of processing,adjust output level, and set the balancebetween compression and leveling. That's it.The COMPELLOR" will then provide completedynamic control-smooth, inaudible compres-sion, increased loudness, freedom from con-stant gain riding, and the desired density-all

automatically. Its unique circuitry actuallyenhances transient qualities, making evenheavy processing undetectable.

This smart, versatile, cost effective processoris equally at home in broadcast pre-processing,microphone control, audio production, tapeduplicating, live sound and film dubbing; pro-ducing the "sound" audio engineers havealways sought but seldom found.

The remarkable Aphex Aural Exciter is a uniqueproprietary audio processing device that makesuse of highly advanced psychoacoustic princi-pals to effectively restore and enhance audiopresence, brightness and intelligibility. The pat-ented psychoacoustic process creates theperception of an increase in mid and high fre-quency energy, with no actual increase inpower or level.

The Aural Exciter can produce dramaticallyimproved clarity, dimension and character inany sound system or application. It can alsoreduce distortion in PA. and sound reinforce-ment applications by providing increased pen-etration and audibility at reduced power levels.The device can be added to virtually any newor existing system with no danger of overload-

ing other components or triggering compres-sors or limiters.

The Aural Exciter is a single-ended process,requiring no decoder. Once encoded, copiesmade from a processed tape sound every bitas good as the original.

The Aphex Aural Exciter is available in threemodels, each is specially designed for a speci-fic application.

APHEX IISThe Studio Aural Exciter is engineered for thesophisticated recording and production studio,as well as advanced sound reinforcement ap-plications. In the studio, the Aural Exciter effec-tively restores the presence and clarity whichthe recording process removes, reviving thatbright, unmistakable "live" quality. It can alsomake certain segments "stand out" withoutactually being louder. Used typically in stereomixdown situations, this latest version of theAural Exciter features increased flexibility soit's ideal for virtually all types of programmaterial, from the hardest rock and roll, to thesubtlest movie dialogue and sound effects.

The Aural Exciter is also well suited to stageand concert use. It can make any PA. systemsound much cleaner, brighter and intelligiblewithout adding any level or feedback to thehouse or monitor system. It is particularly effec-tive in filling acoustic spaces to eliminate deadspots. The device cleans up sound in overlyreverberant halls and makes speaker locationmuch less critical.

APHEX II-BThe Broadcast Aural Exciter has all the remark-able features and capabilities of the Studiounit, plus complete R.F shielding and safetybypass relays in the event of power failure.Designed specifically for on-air use, this unitprovides AM stations with the clarity andbrightness of FM, while restoring to FM thenaturalness and openess normally lost dueto processing.

The most impressive aspect of the AphexBroadcast Aural Exciter is the fact that thelower the quality of the playback system, thebetter the comparative benefit derived. Thesound of your broadcast will satisfy the mostdemanding audiophile, and at the same timegrab the attention of the rush-hour commuter.

APHEX AURAL EXCITER TYPE B

The Aural Exciter Type B is engineered for lessdemanding situations. It utilizes the samepsychoacoustic principles to make AuralExcitement available to small clubs, studios,hails, restaurants, musicians, tape duplicatorsand sound contractors operating on a moremodest budget. Retaining the most importantfeatures of its bigger brothers, the Aural ExciterType B is a small, lightweight package withextensive capabilities limited only by the user'simagination.

SVST€fnSLTD.13340 Satlcoy St. - North Hollywood, California 91605 - (818) 765-2212 - TWX: 910-321-5762

MODULAR PROCESSING

EQF-2The EQF-2 combines a 3-band sweep equalizerwith a sweep Hi and Lo pass filter section. TheEQ has switchable peak/shelf on the Hi and Losections, and reciprocal 12 dB of cut and booston all sections. The filters are second orderButterworth and can be switched separatelyfrom the EQ section.SPECIFICATIONSFREQ.RESPONSE:THD & IMD:NOISE:FILTERS:

EQ LOW:MID:HI:

MAX. I/O:

SIZE:WEIGHT:

± 1dB 20 Hz-20 kHz all sections inBelow 0.1% at max. I/O-123 dB below max. I/OHi pass 20-500 HzLo pass 7-20 kHz25-500 Hz250-5kHz1-20kHz+20 dBm (+30 dBm with opt.Jensen xfrmr)1-1/2" x 5-1/4" x 6" (industry standard)2 lbs.

CX-1The CX-1 is a very versatile module combininga 'soft knee" compressor/limiter with a switch-able expander/gate. The CX-1 uses the proprie-tary Aphex VCA chip to provide an extremelyclean overall sound. The expander is adjustablefrom 0 to 100 dB of expansion (gating) and isthe only noise gate on the market that can beguaranteed not to click or pop. The unit fea-tures a multi-functiona! LED display that indi-cates input, output, compression or expansionlevels.SPECIFICATIONS

2521-OPERATIONAL MODULE

The 2521 Operational Module is a high speed,high output, short circuit proof buffer that takeson the characteristics of the IC that is pluggedinto it. It is current limited and can put out a fullwatt of power into a 62 ohm load.FEATURES700% Field-repairable100% short circuit proofGreatly improved overload characteristicsBuilt-in power decouplingSocketed IC eliminates obsolescenceExtremely low noise currentSPECIFICATIONSBANDWIDTH:THD (at clipping -1 dB):IMD:GAIN:SLEW RATE:OUTPUT NOISE:MAXIMUM INPUT:MAXIMUM POWER OUTPUT:MAXIMUM VOLTS OUTPUT:MAX. SUPPLY VOLTAGE:

4MHz0.02%0.02%50,000 Min.>10 vlfi Sec.-113 dBm30 Volts P-P1 Watt (+30 dBm)Supply -4voltsP-P±18 volts(with LF 351)

"High voltage, high output versions are available.Consult the factory for details.

(Preliminary Data)

MTA 401 SUPERMATCHED QUAD ARRAY

The MTA 401 is a tightly matched, junction iso-lated NPN transistor array with an order ofmagnitude improvement over conventional dis-crete and monolithic arrays. Most operatingparameters approach theoretical limits makingthe MTA 401 an extremely attractive packagefor countless high quality audio applicationssuch as mic, tape head and phono pre-amps,precision OTA's and multipliers as well as manyinstrumentation uses.

SPECIFICATIONSNOISE:VBE MATCHING:hFE MATCHING:

1.2nV/jHz@ 2mA Icto 25/vV

7%

BANDWIDTH:THD, IMD:NOISE:MAX I/O:

SIZE:

WEIGHT:

± 1dB 20-20 KHz all sectionsLess than 0.2% at max I/O-85 dBm+20 dBm (+30 dBmwith optional Jensenxfrmr)7-7/2" x 5-7/4" x 6"(industry standard)2 lbs.

R-1The R-1 holds 10 Aphex modules and providesbarrier strip access to all inputs and outputs.Power and ground are bussed.

4B-1

PS-3

Self-powered, the 4B-1 is for the mobileengineer. It holds 4 Aphex modules and has abuilt-in patch board on the rear with 1/4" andT-T size jacks.

The PS-3 is a ± 16V @ 3.4A regulated supplywith OVP that will power two R—1 racks.

VCA PRODUCTS

1537A VCA IC new low price!The 1537A is the only monolithic Class Avoltage-controlled attenuator on the markettoday. Its patented design features extremelylow distortion, low noise, high stability andwide dynamic range. It can provide more than100dB of attenuation at +20 dBm. Its high slewrate gives low T.I.M. and makes it useable fromDC to 50 MHz.SPECIFICATIONS

VCA 505

BANDWIDTH:THD:IMD:NOISE:MAX. ATTENUATION:

DC to 50 MHz0.004% TYP0.03% TYP- 90 dBv worst case>100 dB, DC -200 kHz

The VCA 505 is an expanded version of thehighly-acclaimed 1537A Voltage ControlledAttenuator. It utilizes a 15-pin card edge mountpackage for easy installation, has multiplebufferred control inputs for maximumversatility, and requires no additional circuity.SIZE: 2.75" high x 2.85"

deep x .72" wide

VCA 500A

The new VCA 500 A utilizes a 1537AVCAICtosignificantly improve the performance andoverall sound quality of the MCI JH-500 seriesconsole. Conversion takes only a few minutesper channel with plug-in convenience.

APHGC svsrems LTD.13340 Saticoy St. - North Hollywood, California 91805 - (818) 765-2212 - TWX: 910-321-5762

T H E C O M P E L L O R

Parts List and Diagrams

13340 Saticoy St. • North Hollywood, CA 91605 • (213) 765-2212 • TWX: 910-321-5762

I/O SL PROCESSING CIRCUITS

I/O PROCESSING CIRCUITS

PARTS LIST

RESISTORS

RvlOlR101R102R103R104R105R106R107R108R109R110R i l lR112R113R114R115R116

R202R203R204R2O5R206R207

- 10K 10 him- 100K 1%- 100K \% -- 20K01%- 20K01%- 13K31%- 13K3 1%- 10K0 1%- 10K0 1%- 2K871%- 13K3 l°o- 34K2 1%

not used- 10K01%

not used- 10KO1%- 150R

- 10KO- 10KO- 15K0- 56R- 1M0- 33KO

R117R118R119R120R121R122R123R124R125R126R127R128R129R130R131R132R133

R208R209R210R211R212R213

3K32 1%- 3K32 1%- 330K- 270K

3K32 1%- 3K32 1%- 46K4 1%- 20K0 1%- 13K2 1%- 13K2 1%- 4K991%- 4K991%- 10K0 1%- 21R5 l?o- 10K0 1%- 150R- 20K0 1%

1K0- 10K0- 10K0- 10K0- 1K0- 10K0

R134 -R135 -R136 -R137 -R138 -R139 -R140 -R141 -R142 -R143 -R144 -R145 -R146 -R147 -R148 -R149 -R150 -

R214 -R215 -R216 -R217 -R218 -R219 -

825R 1%1K0 1%

34K010K02K72K74K71K01M0

150R1K01K01M0

10K0150R

47 KO10K0

10K01M0

10K02K02KB

750R

R151 -R152 -R153 -R154 -R155 -R156 -R157 -R158 -R159 -R160 -R161 -R162 -R163 -R164 -R185 -R166 -R167 -

R220 -R221 -R222 -R223 -R224 -R225 -

10K01K0 1%

20K0 1%16K2 1%9K31 1%4 K 9 9 1 %2K87 1%10K0 1%10K0 1%

56Ofi 1%10K0 1%10K0 1%10K0 1%10K0 1%

lOOK 1%2K72K7

2K01K25M61K0

10K022 KO

R168 -R169 -R170 -R171 -R172 -R173 -R174 -R175 -R176 -R177 -R178 -R179 -R180 -

, R181 -R182 -R183 -R184 -

R226 -R227 -R228 -R229 -

10R10R10R10K010R10K0 1%10K0 1%10K0 1%10K0 1%

lOOK 1%2K72K7

10R10R10R10 KO10R

10K010K0

1K01K0

Resistors J-W, 5%, except as specified. R - Ohm; K = K-Ohm; M = M-Ohm

CAPACITORS

C101 - 150pfC102 - 150pfC103 - 22uf 25VC104 - 22uf 25VC105 - 20pfC106 - 20pfC107 - 20pfC108 - 20pfC109 - lOOuf 25V

C201 - luf tantC202 - 47pfC203 - luf tantC204 - 47pf

C110 - 20pfc m - iopfC112 - lOpfC113 - O.OOlufC114 - O.OlufC115 - O.OlufC116 - 20pfc m - 20PfC118 - 100uf/25V

C205 - luf, tantC206 - 4. 7uf'25VC207 - lOpfC208 - 47pf

C119C120C121C122C123C124C125C126C127

C209C210C211C212

- lOOuf, 25V- lOpf- lOpf- 20pf- 20pf- 20pf- 20pf- 22uf 25V- 22uf 25V

- luf. tant- 0.15uf- 0. luf- O.luf

C128 - 22ufC129 - 22ufC130 - lOOufC131 - lOOufC132 - lOOufC133 - lOOufC134 - 330ufC135 - 330ufC136 - lOOuf

C213 - O.lufC214 - O.lufC215 - O.lufC216 - O.luf

25V25V25V25V25V25V25V25V25V

C137 - lOOuf 25VC138 - O.lufC139 - O.lufC140 - O.lufC141 - 0. lufC142 - 0. lufC143 - O.lufC144 - O.lufC145 - O.luf

C217 - lOOuf 25VC218 - lOOuf 25V

tant = tantalum capacitor

TRANSISTORS

QlOlQ102

Q201 •

- 2N3906 Q1032N3906 Q104

• J113 Q202

- 2N3904- MJE181

- J113

Q105 -0106 -

Q203 -

MJE171MJE181

2N3906

Q107 - MJE171

ICs, DIODES, CHOKE

I C s : U101)U102>U103,U106,U107,U201,U202,U203,U204 = LF353; U104 = 1537A U105 = NE5532N

DIODES : D101,D102,D103,D104,D105,D106,D107,D108,D109,Dm,D112,D113 = 1N914B DUO = 1N4003

0201,0203,0204,0205,0206,0207,0208,0209 = 1N914BCHOKE: Special, Aphex Part # 72-003

CONTROL SL DISPLAY CIRCUITS

PARTS LISTRESISTORS

Rv301Rv401R301 -R302 -R303 -R304 -R305 -R306 -R307 -

R401 -R402 -R403 -R404 -R405 -R406 -R407 -R408 -R409 -R410 -

10Klinear

1K020K0

1K05K6

33K01OKO1OKO

1KO20K0

1KO5K6

33KO10KO1OKO

1OOK1OOK

1KO

Rv302Rv402R3O8 -R3O9 -R31O -R311 -R312 -R313 -R314 -

R411 -R412 -R413 -R414 -R415 -R416 -R417 -R418 -R419 -R420 -

1OKaudio1OOK1OOK

1KO3K6

1OKO10OK

1KO

3K61OKO

1OOK1KO3K6

1OKO1OOK

1KO1OKO

820R

Rv303Rv403 ~R315 -R316 -R317 -R318 -R319 -R32O -R321 -

R421 -R422 -R423 -R424 -R425 -R426 -R427 -R428 -R429 -R430 -

3Klinear

3K61OKO

1OOK1KO

1OKO82OR

4K7

4K71OKO2OKO

820R5K65K61KO1KO

1OKO33KO

Rv404 -R322 -R323 -R324 -R325 -R326 -R327 -R328 -

R431 -R432 -R433 -R434 -R435 -R436 -R437 -R438 -R439 -R440 -

1OK rev

1OKO20K0

820R5K65K61KO1KO

3K68K25

"57K6"8K25

57K633K0

3K615OR1OOK1OOR

audio

R329 -R33O -R331 -R332 -

R441 -R442 -R443 -

1 % R444 "R445 -R446 -R447 -R448 -R449 -R450 -

1OKO1OOK10OK

2OKO

10OK1KO2M2

1OKO1KO2K02K0

1OOR15OR

56R

Fixed resistor {W, 5% R = Ohm; K = K-Ohm; M = M-Ohm

CAPACITORS

C3O1 -C3O2 -C303 -

C401 •C4O2C403C4O4 -C4O5 -

2Opfluf/tantluf/tant

2Opf- luf/tant- luf/tant• 2Opf- 2Opf

C304 -C3O5 -C3O6 -

C406 -C407 -C408 -C409 -C410 -

2Opf2Opf

22uf/25V

22uf/25V100uf/25V100uf/25V100ul/25V100uf/25V

C307 -C308 -C309 -

C411 -C412 -C413 -C414 -C415 -

100uf/25V100uf/25V100uf/25V

O.lufO.lufO.lufO.lufO.luf

C31O - 100uf/25VC311 - O.lufC312 - O.luf

C416 - lOpfC417 - 100uf/25VC418 - lOpfC419 - 100uf/25VC42O - 4.7uf/25V

C313C314

C421

- O.luf- O.luf

- luf/tant

tant = tantalum capacitor

TRANSISTORS

Q3O1 - 2N39O6Q302 - 2N39O6Q3O3 - 2N3906

Q401 - 2N39O6Q4O2 - 2N39O6Q4O3 - 2N3906

Q304 - 2N39O6Q305 - 2N3906Q306 - 2N3906

Q404 - 2N3906Q4O5 - 2N39O6Q4O6 - 2N39OC

Q307 - 2N3906Q3O8 - 2N39O6Q209 - 2N3906

Q407 - 2N3906Q408 - 2N3906Q409 - 2N39O6

Q31O - 2N39O6Q311 - J113Q312 - J113

Q410 - 2N39O6Q411 - J113Q412 - J113

Q313 - 2N39O4Q314 - 2N39O4

Q413 - 2N39O4Q414 - 2N39O4

ICs, DIODES, LEDs

I C s : U301,U302,U303U401, U4O2, U4O3, U408, U409 = LF353

U304, U305U404,U405 = 3914

U306.U307U406,U407 = 3915

DIODES:through 410 - lN6551AorB D311.D312

D411,D412,D413,D414,D415= 1N914B

L E D s :LD301 th LD310 T-13/4LD401 th LD410 = Bicolor

LD413 Red/Gr

LD311 T-13/4LD411 Red

LD312LD412 =LD415

T-13/4Yellow LD414 =

T-13/4Green

LD416LD417 =LD418

T-lGreen

SWITCHES

ALL SWITCHES = 4PDT latching, non-shorting, Alps SUJ Series

POWER SUPPLY