PRESONUS VXP - User manual

PreSonus Audio Electronics | 7257 Florida Blvd, Baton Rouge, LA 70806
T 225.216.7887 F 225.926.8347 | www.presonus.com
Product Reviews
Electronic Musician, June 2001
PreSonus VXP
By Myles Boisen
In the race to capture a share of your gear budget, many manufacturers have recently
rolled out flashy, high-powered, channel-strip-style processors oriented toward vocal
recording. The most stripped-down hybrid voice processors offer a single microphone
preamp, a compressor, and an equalizer; as you move up the scale, the units typically
provide better components and more features.
Among budget voice processors that cost less than $1,000, what you typically pay for
is a single, proven feature - for example, a good preamp or an acclaimed compressor
- with a mixed bag of mediocre extras thrown in. The single-channel PreSonus VXP
breaks the budget mold by offering a bountiful selection of high-quality, genuinely
useful processing stages, starting with a mic preamp that gives the top contenders a
run for their money.
STRING OF TOOLS
With its thick cool blue aluminum front panel and brushed aluminum knobs, the VXP
matches the look of the company's MP20 stereo mic preamp. The front panel is
divided into six segments according to function and has a big glowing "red eye" push-
button power switch on the far right.
From left, first up is the mic preamp section, which provides a continuously variable
gain knob with 0 to 60 dB of gain marked in 10 dB steps. Next is the proprietary
IDSS control, which ranges from 0 to 100 percent. According to PreSonus, the IDSS
control allows for manual adjustment of the drain current on the input FET amplifier,
thus increasing even harmonic distortion as IDSS processing is added. That unusual
circuit modification is not intended to produce overload distortion associated with
guitar amps and fuzz boxes but rather to emulate the thickening effect of even-order
harmonic boosting in vacuum tubes.
Just above the gain and IDSS controls is a green eight-segment LED that 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 no polarity-reverse switch, but 48V phantom

PreSonus Audio Electronics | 7257 Florida Blvd, Baton Rouge, LA 70806
T 225.216.7887 F 225.926.8347 | www.presonus.com
Product Reviews
power and a 20 dB attenuation pad are selectable from plastic push-button switches
that glow green when engaged.
The VXP's compressor portion traces its lineage to PreSonus' popular Blue Max
Smart Compressor. But unlike the Blue Max, which offers 15 presets and a manual
setting that allows for control over conventional parameters (ratio, attack time,
release time, and so on), the VXP's compressor provides only 16 presets: 5 Light, 5
Medium, and 6 Heavy. The presets are maximized for vocal applications, but
according to PreSonus, they are useful in other applications as well. The manual
doesn't disclose the individual presets' exact parameters, but it does give 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 general applications.
The compressor's input and output (make-up) gain controls are located on a
concentric, dual-pot control. By letting the signal level's adjustment be above or
below a preset threshold (determined by the compressor preset), the input-gain knob
functions essentially as a threshold control - a rather important point the manual fails
to mention. Input gain can vary from -12 dB to +18 dB; make-up gain is adjustable
from -20 dB to +20 dB. A backlit In/Out switch (bypass) allows for A/B comparison
of compressed and uncompressed signals. An eight-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 of background noise - is
simple but surprisingly effective with just two controls on one concentric shaft. The
outer threshold ring adjusts the signal level at which the expander starts to work,
covering the entire dynamic range of most audio between its extremes of "off" (-70
dBu) and maximum of +20 dB. PreSonus thoughtfully gave the expander a ratio
control, which allows continuous manipulation of gated signals' gain reduction, from a
subtle 1:1 setting to the complete muting offered by an infinity:1 ratio. LED
metering is provided at four gain-reduction points: -3, -6, -12, and -24 dB.
A dual-function concentric knob also controls the de-esser. The inner shaft selects
frequency (continuously variable from 800 Hz to 8 kHz) and is targeted at prominent
or overly sibilant esses common in many vocal recordings. The de-esser's threshold
setting (-40 dB to +20 dB or "off") reduces gain only at the offending frequency and
typically passes bass and midrange frequencies untouched so that the de-essed signal
loses its sizzle but not its strength. A four-section meter - with green LEDs at -1, -3,
-6, and -12 dB - indicates the module's frequency-specific gain reduction. The de-
esser and expander sections do not provide a bypass, but they can be disabled by
setting their respective threshold controls to the clearly marked "off" positions
(counterclockwise for the expander, clockwise for the de-esser).
The VXP's 4-band equalization is implemented as separate high and low shelving
(fixed frequency at 100 Hz and 12 kHz respectively, -12 to +12 dB gain on both) and

PreSonus Audio Electronics | 7257 Florida Blvd, Baton Rouge, LA 70806
T 225.216.7887 F 225.926.8347 | www.presonus.com
Product Reviews
two concentric, semiparametric midrange controls. 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 is
included, 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-level control (-70 to +10 dBu), and an output meter
identical to the eight-segment LED array in the mic preamp section. No meter
indicates gain reduction for the peak limiter.
GOOD CONNECTIONS
The VXP's rear-panel connections are simple: one balanced XLR microphone input,
separate _-inch balanced TRS send-and-receive insert jacks, and XLR and _-inch
output jacks for balanced or unbalanced operation, respectively. The insert return can
bring a line-level signal into the VXP for processing, and the send jack can also be
used when clean output (that is, without channel-strip processing) from the mic
preamp is desired. (The manual doesn't mention where the insert return point is in
the VXP circuit, but through testing I determined that it comes after the mic preamp
and before the compressor and subsequent options.) The line-input level also shows
up on the mic preamp input-level meter.
There is no provision for -10 dBV consumer-level output, though the master gain
control could easily be used to reduce gain to a level appropriate for -10 input
devices. A standard IEC power connector and AC voltage selector are on the rear
panel, as is a bay for the optional VXPD2496 digital-output converter and card
module ($399).
CARD-CARRYING MEMBER
I tested two VXPs: one with the digital card packaged separately and one with the
card already in place. The output card is a stereo converter, meaning that you need
to buy only one card to record digitally from a pair of VXPs. Just the same, I wanted
to try my hand at installing the VXPD2496 in the stock unit. The module was in place
in less than ten minutes, and the only difficulty I had was getting some screws out,
thanks to the VXP's solid construction.
VXP Specifications
Inputs (1) balanced XLR (mic); (2) balanced/unbalanced 1/4" TRS (send and
receive)
Outputs (1) balanced XLR; (1) balanced/unbalanced 1/4" TRS
Power Supply internal
Dimensions 1U 5 7" (D)
Weight 8 lbs.

PreSonus Audio Electronics | 7257 Florida Blvd, Baton Rouge, LA 70806
T 225.216.7887 F 225.926.8347 | www.presonus.com
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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 provides AES/EBU and
S/PDIF output jacks, BNC word-clock In and Out, a _-inch TRS right-channel analog
in, an internal/external sync LED, and separate bit-rate and sampling-frequency
selector switches. Green LEDs indicate selected bit rates of 16, 18, 20, and 24, in
addition to all common sampling frequencies (44.1, 48, 88.2, and 96 kHz). All that,
two PC boards, and a Crystal Semiconductor 5396 converter chip are mounted on a
1_-by-4_-inch panel that attaches to the VXP chassis with two Phillips screws. The

PreSonus Audio Electronics | 7257 Florida Blvd, Baton Rouge, LA 70806
T 225.216.7887 F 225.926.8347 | www.presonus.com
Product Reviews
VXPD2496 comes with a three-page manual, which includes installation instructions,
brief operating notes, and specifications.
When using two VXPs in tandem, the unit housing the VXPD2496 module is
automatically assigned to the left digital channel and the other VXP (or any other
preamp, for that matter) must be connected to the TRS right-channel analog input on
the converter card. The converter could also be used on a line-level stereo mix by
applying the left and right mix-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-tracking session. With the
exception of the IDSS circuit, every control and connection point was easy to
comprehend without my cracking the manual. The unit weighed more than I
expected, partly because of the massive Italian-made torroidal transformer visible
through the top vents. On a Fender guitar/Fender amp rig, miked with a Royer R-121
ribbon microphone, the VXP issued a solid, authoritative tone that matched a
previous track recorded with the same mic through a Drawmer 1960, one of my
favorite guitar preamps.
A female vocalist sounded deliciously airy through a BLUE Bottle microphone (with
B7 capsule) paired with the VXP. For her lead vocal and background tracks, I used
some limiting and low-shelving EQ to polish the signal going to tape, along with the
expander to minimize headphone bleed. The modules were responsive and easy to
use. However, I probably dialed in conservative settings because of the EQ section's
lack of gain markings and metering for the limiter. In that regard, as with many
other preamps I've used, the VXP is more an intuitive rather than an exacting unit.
Although I'm happy to rely on my ears when adjusting a knob, having calibrated
markings on the VXP's parameters would be nice.
I also compared the VXP to a Neve 1272 preamp on an acoustic-guitar lead miked
with an Oktava MK 219 condenser mic. The VXP didn't have the up-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 MK 219. I was consistently impressed by the VXP's
ability to stand in for much more expensive preamps during the testing phase.
Although I generally avoid dynamic processing and equalization going to tape, most
of the VXP's processing options met or surpassed my expectations in terms of
professional sound quality, low noise, and absence of coloration. My only gripe is
about some of the sections' physical implementation - specifically, the concentric pots
required to fit everything onto the VXP's crowded 1U faceplate.
Gain controls for the shelving and bell EQ are detented at their zero settings, but
curiously, the compressor and master-gain knobs are not. On the compressor, even
with perfect visual alignment of the input and output knob settings at zero, engaging

PreSonus Audio Electronics | 7257 Florida Blvd, Baton Rouge, LA 70806
T 225.216.7887 F 225.926.8347 | www.presonus.com
Product Reviews
the module on below-threshold signals changed the overall level and introduced
switching noise.
In addition, the 16 compression presets are not labeled, which complicates
repeatability. If it were my unit, I'd be tempted to mark the 16 positions with a
grease pencil, for example, L1, L2, L3, and so on.
With compressor gain at unity, a 0 dB line input produced an average of -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 on for good results, with no negative impact
on a variety of signals. But at -6 dB in the Heavy settings, the VXP compressor
started to pump audibly and it imparted a sibilant edge to a full-spectrum music mix.
The relatively simple de-esser and expander functions are useful and perform on par
with the best-available modules found in other multi-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, which controls
threshold, to the off position without accidentally moving the inner knob, which
selects the de-ess frequency. Furthermore, that dial's only intermediate numerical
value is a zero marking at about two o'clock, which again complicates repeatability.
Similarly, the expander controls have no intermediate marks except for a 2:1 ratio
designation.
FULL STEAM AHEAD
The VXP's 4-band equalizer - a first on any PreSonus product - is also quite effective
and remarkably lavish, especially considering the unit's price. Although there was no
special magic in the high-shelf range, the low-shelving control let me make beefy
bass boosts without adding unwanted flab to a mix. In addition, the high Q option
provided enough surgical precision to reveal previously unheard mixing and mastering
flaws in some of my older recordings. Thankfully, all EQ knobs are zero-detented and
there are helpful frequency markings around the perimeter of the split-shaft bell EQ
controls.
Lack of gain-reduction metering aside, the PreSonus limiter sounds amazingly good
under all conditions. During sessions it was always subtle and completely transparent,
putting a soft touch on peaks without 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's
output meter and metering on the DAT, the limiter's gain ceiling is not the inflexible
type found on most brickwall-type limiters. What the VXP lacks in control-knob
precision, it gains in intelligent designs that sound good.
The VXP's only disappointing feature is the IDSS control. In loudspeaker and session
tests, I heard no favorable coloration added by that circuit. At 50 percent, the
process is audible, serving to take a little edge off a signal - as would a deep-cut,

PreSonus Audio Electronics | 7257 Florida Blvd, Baton Rouge, LA 70806
T 225.216.7887 F 225.926.8347 | www.presonus.com
Product Reviews
high-shelving EQ set to a corner frequency of 2 kHz. At 100 percent, it significantly
dulled and attenuated a full-music mix and produced a thick-and muddy-sounding
midbass boost that pushed the kick drum forward. Granted, that circuit is probably
not intended for stereo-program material; but even on individual tracks, the IDSS
produced no audible enhancements.
NOT QUITE CONVERTED
During a loudspeaker test for compatibility and sonic character of the VXPs through
the onboard converter card, matching the units' output levels using knob calibrations
and the LEDs was easy. Because the preamp gains are continuously adjustable, minor
tweaks to the left-right balance were a cinch. For stereo recording to digital media,
the VXPs provided dramatic headroom, given that output levels ranging from 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 Apogee PSX-100, a
much higher-end converter. For that test, I recorded music samples to DAT through
the VXPD2496, followed by the same samples with identical preamp settings through
the PSX-100. With the Apogee converter as the only variable in the signal chain, the
level to DAT dropped dramatically. It didn't take long to figure out why - the
VXPD2496 was simply calibrated to a much higher reference level than usual.
PreSonus explained that the latest revision of its A/D converter card was adjusted to
conform to the standard reference level of 0 dB equals -18 dBFS. PreSonus sent me
an upgraded VXPD2496, and it performed as promised. But with either VXPD2496
version, the unit's +24 dB of headroom is sufficient to drive analog or digital inputs
to maximum levels, regardless of the converter or reference level used.
With levels equalized through the PreSonus and Apogee converters, samples from
Steely Dan's "Green Earrings" revealed intriguing differences. Tonally, though the
snare drum was edgier through the VXP digital card, the two converters sounded
close to identical when recording the same program at maximum levels to 48
kHz/16-bit DAT. The major discrepancy was in the reverb on Donald Fagen's voice.
The reverb was lush through the Apogee PSX-100, and it always sustained through
the breaks between vocal lines. The same section when heard through the PreSonus
converter, however, sounded like a much drier mix. The reverb decay was shorter
and didn't bridge the gap between lyrics.
That result suggests potential resolution problems in the onboard VXP converter. The
higher bit rates in the VXPD2496 will improve the unit's resolution, but based on my
comparison tests, I would be wary of using the PreSonus converter for professional
classical recording and other critical stereo-recording applications that require
accurate room-sound reproduction and subtle ambient details.
MANUAL OVERDRIVE

PreSonus Audio Electronics | 7257 Florida Blvd, Baton Rouge, LA 70806
T 225.216.7887 F 225.926.8347 | www.presonus.com
Product Reviews
The VXP manual, though adequate and well intentioned, unfortunately suffers from
omissions and errors. Aside from the lack of specifics about the compression presets
and use of the compressor input-gain control, the manual mistakenly groups
condenser and ribbon mics, stating that "condenser and some ribbon microphones
require external power to preamplify the microphone acoustic pickup. These
microphones typically have much higher output than dynamic microphones." Not only
do ribbon mics typically produce lower output than ordinary dynamic microphones but
they're also actually dynamic mics. Furthermore, phantom power should not be
applied to ribbon microphones.
The manual also makes the highly debatable assertion that "the -20 dB pad is almost
always necessary when close-miking." I especially took issue with the following
statement about the IDSS circuit: "This remarkable effect gives you the sound of a
tube without the headache of uneven performance often encountered with vacuum
tube devices."
HEADS UP
The PreSonus VXP is a powerful, high-quality voice processor with loads of features
yet a surprisingly modest price tag. It provides a Class A mic preamp, an IDSS circuit
said to emulate tube distortion, a smart compressor with 16 presets, an expander, a
de-esser, a 4-band semiparametric equalizer, and a peak limiter. All the processing
stages but one, the IDSS circuit, are well implemented, useful, and highly usable. I
was impressed with the VXP's mic preamp, which provides as much or more clean
gain than many top-dollar units. At microphone or line level, there is plenty of
headroom for analog or digital output (the latter for using the optional VXPD2496
converter card). I was also impressed with both the flexibility and transparency of
the VXP's peak limiter. Personal-studio operators and picky professionals should note
the VXP's competitive sound quality.
To pack such a dense array of features into the VXP's single-rackspace control
surface, PreSonus used concentric dual-function pots in the dynamic and EQ
processing sections. The face is still a bit cluttered, meaning you have limited finger
space and calibration marks are sometimes sparse and hard to decipher. To fit in all
the marks, meters, and switches I'd like to see, the VXP would have to be a bigger
beast with a larger price tag. As it is, the drawbacks are minor compared with the
wealth of high-performance circuitry PreSonus squeezed into an affordable package.
Myles Boisen is a guitarist, producer, and composer, and is head recording/mastering
engineer at Guerrilla Recording and the Headless Buddha Mastering Lab in Oakland,
California. He can be reached through e-mail at mylesaud[email protected].
RATING PRODUCTS FROM 1 TO 5

PreSonus Audio Electronics | 7257 Florida Blvd, Baton Rouge, LA 70806
T 225.216.7887 F 225.926.8347 | www.presonus.com
Product Reviews
FEATURES 4.0
AUDIO QUALITY 4.5
EASE OF USE 4.0
VALUE 5.0
PROS: Many fully professional features at a budget price. Excellent mic preamp with
lots of gain. Ample +24 dB headroom. Very useful compressor, de-esser, expander,
and equalization functions. Excellent limiter circuit. Insert allows send and return
and line-level input. Single VXPD2496 converter card works for stereo signals.
CONS: Compression presets offer limited options. Some processing sections don't
have bypasses for A/B comparison. Not all gain pots are detented. No meter for
limiter. No polarity reverse. IDSS effect produces no audible enhancement.
VXPD2496 converter card doesn't convey low-resolution details well.
This article was originally published in the June 2001 issue of Electronic Musician
magazine, a product of Primedia Business Magazines and Media, and is reprinted
with the permission of its publisher. All rights reserved.