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Presonus VXP voice processor

6/1/2001

In the race to capture a share of your gear budget, manymanufacturers have recently rolled out flashy, high-powered,channel-strip-style processors oriented toward vocal recording. Themost stripped-down hybrid voice processors offer a single microphonepreamp, a compressor, and an equalizer; as you move up the scale, theunits typically provide better components and more features.

Among budget voice processors that cost less than $1,000, what youtypically pay for is a single, proven feature — for example, agood preamp or an acclaimed compressor — with a mixed bag ofmediocre extras thrown in. The single-channel PreSonus VXP breaks thebudget mold by offering a bountiful selection of high-quality,genuinely useful processing stages, starting with a mic preamp thatgives the top contenders a run for their money.

STRING OF TOOLS

With its thick cool blue aluminum front panel and brushed aluminumknobs, the VXP matches the look of the company's MP20 stereo micpreamp. The front panel is divided into six segments according tofunction and has a big glowing “red eye” push-button powerswitch on the far right.

From left, first up is the mic preamp section, which provides acontinuously variable gain knob with 0 to 60 dB of gain marked in 10 dBsteps. Next is the proprietary IDSS control, which ranges from 0 to 100percent. According to PreSonus, the IDSS control allows for manualadjustment of the drain current on the input FET amplifier, thusincreasing even harmonic distortion as IDSS processing is added. Thatunusual circuit modification is not intended to produce overloaddistortion associated with guitar amps and fuzz boxes but rather toemulate the thickening effect of even-order harmonic boosting in vacuumtubes.

Just above the gain and IDSS controls is a green eight-segment LEDthat indicates preamp gain levels at -28, -14, -9, -3, 0, +3, +9, and+18 dB, with a red LED assigned to the +18 dB value. There is nopolarity-reverse switch, but 48V phantom power and a 20 dB attenuationpad are selectable from plastic push-button switches that glow greenwhen engaged.

The VXP's compressor portion traces its lineage to PreSonus'spopular Blue Max Smart Compressor. But unlike the Blue Max, whichoffers 15 presets and a manual setting that allows for control overconventional parameters (ratio, attack time, release time, and so on),the VXP's compressor provides only 16 presets: 5 Light, 5 Medium, and 6Heavy. The presets are maximized for vocal applications, but accordingto PreSonus, they are useful in other applications as well. The manualdoesn't disclose the individual presets' exact parameters, but it doesgive ratio ranges for the three groupings — Light 1.1:1 to 1.5:1,Medium 1.6:1 to 2:1, and Heavy 2.5:1 to 8:1 — as well as generalapplications.

The compressor's input and output (make-up) gain controls arelocated on a concentric, dual-pot control. By letting the signallevel's adjustment be above or below a preset threshold (determined bythe compressor preset), the input-gain knob functions essentially as athreshold control — a rather important point the manual fails tomention. Input gain can vary from -12 dB to +18 dB; make-up gain isadjustable from -20 dB to +20 dB. A backlit In/Out switch (bypass)allows for A/B comparison of compressed and uncompressed signals. Aneight-segment meter with green LEDs indicates gain reduction at -1, -2,-3, -4, -6, -9, -12, and -18 dB.

A downward expander — designed for smooth, tapered fades ofbackground noise — is simple but surprisingly effective with justtwo controls on one concentric shaft. The outer threshold ring adjuststhe signal level at which the expander starts to work, covering theentire dynamic range of most audio between its extremes of“off” (-70 dBu) and maximum of +20 dB. PreSonusthoughtfully gave the expander a ratio control, which allows continuousmanipulation of gated signals' gain reduction, from a subtle 1:1setting to the complete muting offered by an infinity:1 ratio. LEDmetering is provided at four gain-reduction points: -3, -6, -12, and-24 dB.

A dual-function concentric knob also controls the de-esser. Theinner shaft selects frequency (continuously variable from 800 Hz to 8kHz) and is targeted at prominent or overly sibilant essescommon in many vocal recordings. The de-esser's threshold setting (-40dB to +20 dB or “off”) reduces gain only at the offendingfrequency and typically passes bass and midrange frequencies untouchedso that the de-essed signal loses its sizzle but not its strength. Afour-section meter — with green LEDs at -1, -3, -6, and -12 dB— indicates the module's frequency-specific gain reduction. Thede-esser and expander sections do not provide a bypass, but they can bedisabled by setting their respective threshold controls to the clearlymarked “off” positions (counterclockwise for the expander,clockwise for the de-esser).

The VXP's 4-band equalization is implemented as separate high andlow shelving (fixed frequency at 100 Hz and 12 kHz respectively, -12 to+12 dB gain on both) and two concentric, semiparametric midrangecontrols. The low midrange knob covers three octaves from 90 to 700 Hz,and the high midrange pot spans 450 Hz (marked as .45 kHz) to 5.8 kHz.Bandwidth for each midrange EQ is selectable with a push-button switch,offering Q values of 2.0 or 0.5. A switchable 80 Hz low-cut filter isincluded, and the EQ section can be bypassed through an In button.

The VXP's master section comprises a peak-limiter threshold control(brickwall type, 0 to +24 dBu or “off”), a master-levelcontrol (-70 to +10 dBu), and an output meter identical to theeight-segment LED array in the mic preamp section. No meter indicatesgain reduction for the peak limiter.

GOOD CONNECTIONS

The VXP's rear-panel connections are simple: one balanced XLRmicrophone input, separate ¼-inch balanced TRS send-and-receiveinsert jacks, and XLR and ¼-inch output jacks for balanced orunbalanced operation, respectively. The insert return can bring aline-level signal into the VXP for processing, and the send jack canalso be used when clean output (that is, without channel-stripprocessing) from the mic preamp is desired. (The manual doesn't mentionwhere the insert return point is in the VXP circuit, but throughtesting I determined that it comes after the mic preamp and before thecompressor and subsequent options.) The line-input level also shows upon the mic preamp input-level meter.

There is no provision for -10 dBV consumer-level output, though themaster gain control could easily be used to reduce gain to a levelappropriate for -10 input devices. A standard IEC power connector andAC voltage selector are on the rear panel, as is a bay for the optionalVXPD2496 digital-output converter and card module ($399).

CARD-CARRYING MEMBER

I tested two VXPs: one with the digital card packaged separately andone with the card already in place. The output card is a stereoconverter, meaning that you need to buy only one card to recorddigitally from a pair of VXPs. Just the same, I wanted to try my handat installing the VXPD2496 in the stock unit. The module was in placein less than ten minutes, and the only difficulty I had was gettingsome screws out, thanks to the VXP's solid construction.

VXP Specifications
Inputs (1) balanced XLR (mic); (2) balanced/unbalanced¼" TRS (send and receive)
Outputs (1) balanced XLR; (1) balanced/unbalanced ¼"TRS
Power Supply internal
Dimensions 1U 5 7" (D)
Weight 8 lbs.
MIC PREAMP
Frequency Response 10 Hz-50 kHz
THD + Noise (0% IDSS) <0.003%
THD + Noise (100% IDSS) >0.5%
Noise Floor -97.2 dBu (@ +12 dB gain)
Dynamic Range >115 dB
Headroom +24 dBu
Maximum Gain 36 dB (+12 to + 48 dB)
Attenuation Pad 20 dB (switchable)
Phantom Power 48V
COMPRESSOR
Input Attenuation/Gain -12 to +18 dB
Output Attenuation/Gain -20 to +20 dB
Presets 16
EXPANDER
Threshold Range -70 to +20 dBu
Ratio Range 1:1 to •:1
DE-ESSER
Threshold Range -40 to +20 dBu
Frequency Range 800 Hz to 8 kHz
EQUALIZER
Rumble Filter Cutoff Frequency 80 Hz (-6 dB per octave)
Low Shelving 100 Hz (±12 dB)
Low Midrange 90 Hz-700 Hz (±12 dB)
Low-Mid Q (Bandwidth) 0.5/2.0 octave (switchable)
High Midrange 450 Hz-5.8 kHz (±12 dB)
High-Mid Q (Bandwidth) 0.5/2.0 octave (switchable)
High Shelving 12 kHz (±12 dB)
MASTER
Peak Limit Range 0 to +24 dBu
Output Fader -70 to +10 dB

The VXPD2496 is truly a marvel of miniaturization. It providesAES/EBU and S/PDIF output jacks, BNC word-clock In and Out, a¼-inch TRS right-channel analog in, an internal/external sync LED,and separate bit-rate and sampling-frequency selector switches. GreenLEDs indicate selected bit rates of 16, 18, 20, and 24, in addition toall common sampling frequencies (44.1, 48, 88.2, and 96 kHz). All that,two PC boards, and a Crystal Semiconductor 5396 converter chip aremounted on a 1½-by-4¾-inch panel that attaches to the VXPchassis with two Phillips screws. The VXPD2496 comes with a three-pagemanual, which includes installation instructions, brief operatingnotes, and specifications.

When using two VXPs in tandem, the unit housing the VXPD2496 moduleis automatically assigned to the left digital channel and the other VXP(or any other preamp, for that matter) must be connected to the TRSright-channel analog input on the converter card. The converter couldalso be used on a line-level stereo mix by applying the left and rightmix-bus outputs to the insert-return jacks of two VXPs.

HOLDS ITS OWN

I put the VXP to work right out of the box for a guitar-trackingsession. With the exception of the IDSS circuit, every control andconnection point was easy to comprehend without my cracking the manual.The unit weighed more than I expected, partly because of the massiveItalian-made torroidal transformer visible through the top vents. On aFender guitar/Fender amp rig, miked with a Royer R-121 ribbonmicrophone, the VXP issued a solid, authoritative tone that matched aprevious track recorded with the same mic through a Drawmer 1960, oneof my favorite guitar preamps.

A female vocalist sounded deliciously airy through a BLUE Bottlemicrophone (with B7 capsule) paired with the VXP. For her lead vocaland background tracks, I used some limiting and low-shelving EQ topolish the signal going to tape, along with the expander to minimizeheadphone bleed. The modules were responsive and easy to use. However,I probably dialed in conservative settings because of the EQ section'slack of gain markings and metering for the limiter. In that regard, aswith many other preamps I've used, the VXP is more an intuitive ratherthan an exacting unit. Although I'm happy to rely on my ears whenadjusting a knob, having calibrated markings on the VXP's parameterswould be nice.

I also compared the VXP to a Neve 1272 preamp on an acoustic-guitarlead miked with an Oktava MK 219 condenser mic. The VXP didn't have theup-front attitude of the vintage Neve, but it certainly held its own.It even added some heft to the tone picked up by the rather bright MK219. I was consistently impressed by the VXP's ability to stand in formuch more expensive preamps during the testing phase. Although Igenerally avoid dynamic processing and equalization going to tape, mostof the VXP's processing options met or surpassed my expectations interms of professional sound quality, low noise, and absence ofcoloration. My only gripe is about some of the sections' physicalimplementation — specifically, the concentric pots required tofit everything onto the VXP's crowded 1U faceplate.

Gain controls for the shelving and bell EQ are detented at theirzero settings, but curiously, the compressor and master-gain knobs arenot. On the compressor, even with perfect visual alignment of the inputand output knob settings at zero, engaging the module onbelow-threshold signals changed the overall level and introducedswitching noise.

In addition, the 16 compression presets are not labeled, whichcomplicates repeatability. If it were my unit, I'd be tempted to markthe 16 positions with a grease pencil, for example, L1, L2, L3, and soon.

With compressor gain at unity, a 0 dB line input produced an averageof -1 dB gain reduction in Light programs, -2 to -3 dB in Medium, and-3 to -6 dB in Heavy. Light to Medium compression could be relied onfor good results, with no negative impact on a variety of signals. Butat -6 dB in the Heavy settings, the VXP compressor started to pumpaudibly and it imparted a sibilant edge to a full-spectrum musicmix.

The relatively simple de-esser and expander functions are useful andperform on par with the best-available modules found in othermulti-effects dynamics processors. The de-esser is easy to fine-tune,but the lack of a bypass switch makes A/B comparisons awkward.Considerable finesse is required to twist the outer ring, whichcontrols threshold, to the off position without accidentally moving theinner knob, which selects the de-ess frequency. Furthermore, thatdial's only intermediate numerical value is a zero marking at about twoo'clock, which again complicates repeatability. Similarly, the expandercontrols have no intermediate marks except for a 2:1 ratiodesignation.

FULL STEAM AHEAD

The VXP's 4-band equalizer — a first on any PreSonus product— is also quite effective and remarkably lavish, especiallyconsidering the unit's price. Although there was no special magic inthe high-shelf range, the low-shelving control let me make beefy bassboosts without adding unwanted flab to a mix. In addition, the high Qoption provided enough surgical precision to reveal previously unheardmixing and mastering flaws in some of my older recordings. Thankfully,all EQ knobs are zero-detented and there are helpful frequency markingsaround the perimeter of the split-shaft bell EQ controls.

Lack of gain-reduction metering aside, the PreSonus limiter soundsamazingly good under all conditions. During sessions it was alwayssubtle and completely transparent, putting a soft touch on peakswithout any coloration or grit. Even when I cranked it to the extreme,I noticed no distortion in a full-music mix. Judging by the VXP'soutput meter and metering on the DAT, the limiter's gain ceiling is notthe inflexible type found on most brickwall-type limiters. What the VXPlacks in control-knob precision, it gains in intelligent designs thatsound good.

The VXP's only disappointing feature is the IDSS control. Inloudspeaker and session tests, I heard no favorable coloration added bythat circuit. At 50 percent, the process is audible, serving to take alittle edge off a signal — as would a deep-cut, high-shelving EQset to a corner frequency of 2 kHz. At 100 percent, it significantlydulled and attenuated a full-music mix and produced a thick-andmuddy-sounding midbass boost that pushed the kick drum forward.Granted, that circuit is probably not intended for stereo-programmaterial; but even on individual tracks, the IDSS produced no audibleenhancements.

NOT QUITE CONVERTED

During a loudspeaker test for compatibility and sonic character ofthe VXPs through the onboard converter card, matching the units' outputlevels using knob calibrations and the LEDs was easy. Because thepreamp gains are continuously adjustable, minor tweaks to theleft-right balance were a cinch. For stereo recording to digital media,the VXPs provided dramatic headroom, given that output levels rangingfrom 0 to +3 dB produced maximum levels on my Tascam DA-30 meters.

I also compared the inexpensive VXPD2496 to the A/D on the ApogeePSX-100, a much higher-end converter. For that test, I recorded musicsamples to DAT through the VXPD2496, followed by the same samples withidentical preamp settings through the PSX-100. With the Apogeeconverter as the only variable in the signal chain, the level to DATdropped dramatically. It didn't take long to figure out why — theVXPD2496 was simply calibrated to a much higher reference level thanusual. PreSonus explained that the latest revision of its A/D convertercard was adjusted to conform to the standard reference level of 0 dBequals -18 dBFS. PreSonus sent me an upgraded VXPD2496, and itperformed as promised. But with either VXPD2496 version, the unit's +24dB of headroom is sufficient to drive analog or digital inputs tomaximum levels, regardless of the converter or reference levelused.

With levels equalized through the PreSonus and Apogee converters,samples from Steely Dan's “Green Earrings” revealedintriguing differences. Tonally, though the snare drum was edgierthrough the VXP digital card, the two converters sounded close toidentical when recording the same program at maximum levels to 48kHz/16-bit DAT. The major discrepancy was in the reverb on DonaldFagen's voice. The reverb was lush through the Apogee PSX-100, and italways sustained through the breaks between vocal lines. The samesection when heard through the PreSonus converter, however, soundedlike a much drier mix. The reverb decay was shorter and didn't bridgethe gap between lyrics.

That result suggests potential resolution problems in the onboardVXP converter. The higher bit rates in the VXPD2496 will improve theunit's resolution, but based on my comparison tests, I would be wary ofusing the PreSonus converter for professional classical recording andother critical stereo-recording applications that require accurateroom-sound reproduction and subtle ambient details.

MANUAL OVERDRIVE

The VXP manual, though adequate and well intentioned, unfortunatelysuffers from omissions and errors. Aside from the lack of specificsabout the compression presets and use of the compressor input-gaincontrol, the manual mistakenly groups condenser and ribbon mics,stating that “condenser and some ribbon microphones requireexternal power to preamplify the microphone acoustic pickup. Thesemicrophones typically have much higher output than dynamicmicrophones.” Not only do ribbon mics typically produce loweroutput than ordinary dynamic microphones but they're also actuallydynamic mics. Furthermore, phantom power should not be applied toribbon microphones.

The manual also makes the highly debatable assertion that “the-20 dB pad is almost always necessary when close-miking.” Iespecially took issue with the following statement about the IDSScircuit: “This remarkable effect gives you the sound of a tubewithout the headache of uneven performance often encountered withvacuum tube devices.”

HEADS UP

The PreSonus VXP is a powerful, high-quality voice processor withloads of features yet a surprisingly modest price tag. It provides aClass A mic preamp, an IDSS circuit said to emulate tube distortion, asmart compressor with 16 presets, an expander, a de-esser, a 4-bandsemiparametric equalizer, and a peak limiter. All the processing stagesbut one, the IDSS circuit, are well implemented, useful, and highlyusable. I was impressed with the VXP's mic preamp, which provides asmuch or more clean gain than many top-dollar units. At microphone orline level, there is plenty of headroom for analog or digital output(the latter for using the optional VXPD2496 converter card). I was alsoimpressed with both the flexibility and transparency of the VXP's peaklimiter. Personal-studio operators and picky professionals should notethe VXP's competitive sound quality.

To pack such a dense array of features into the VXP'ssingle-rackspace control surface, PreSonus used concentricdual-function pots in the dynamic and EQ processing sections. The faceis still a bit cluttered, meaning you have limited finger space andcalibration marks are sometimes sparse and hard to decipher. To fit inall the marks, meters, and switches I'd like to see, the VXP would haveto be a bigger beast with a larger price tag. As it is, the drawbacksare minor compared with the wealth of high-performance circuitryPreSonus squeezed into an affordable package.


Myles Boisen is a guitarist, producer, and composer, and is headrecording/mastering engineer at Guerrilla Recording and the HeadlessBuddha Mastering Lab in Oakland, California. He can be reached throughe-mail at mylesaudio@aol.com.

PRODUCT SUMMARY

PreSonus
VXP

voice processor
$799

FEATURES 4.0
AUDIO QUALITY 4.5
EASE OF USE 4.0
VALUE 5.0
RATING PRODUCTS FROM 1 TO5

PROS: Many fully professional features at a budget price.Excellent mic preamp with lots of gain. Ample +24 dB headroom. Veryuseful compressor, de-esser, expander, and equalization functions.Excellent limiter circuit. Insert allows send and return and line-levelinput. Single VXPD2496 converter card works for stereo signals.

CONS: Compression presets offer limited options. Someprocessing sections don't have bypasses for A/B comparison. Not allgain pots are detented. No meter for limiter. No polarity reverse. IDSSeffect produces no audible enhancement. VXPD2496 converter card doesn'tconvey low-resolution details well.

Manufacturer

PreSonus Audio Electronics
tel. (800) 750-0323
e-mail presonus@presonus.com
Web www.presonus.com

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