INSIDE TRACKNTI MR-PRO Minirator
Terry Nelson MIBS reviews the latest versionof the NTI Minirator test signal generator.
he MR-PRO is the latest version ofNTI’s clever analogue signalgenerator aimed at professional
applications for testing and aligning
analogue equipment. It looks similar to theless expensive MR2, but offers considerably
more functionality. The MR-PRO is a nice,chunky piece of equipment that sits
comfortably in the palm of the hand and is
supplied with a plastic rubber shock jacket
and hand strap. The unit is powered bythree AA-sized batteries that fit into an easily
accessible battery compartment, and for
those situations where in situ operation isrequired, an optional mains power supply isavailable; the manufacturer’s model isrecommended for maximum efficiency andisolation.
The top face of the MR-PRO generator
features a large LCD screen plus a control
area consisting of a sizeable rotary wheel(with central Enter button) for navigation,
flanked by two pushbuttons on either side
(Esc and Level to the left, with Wave andFreq to the right). Three more pushbuttons
arranged in an arc below switch sensitivity,power and mute the output. Turning thewheel clockwise scrolls through the menu
screens from top to bottom and left to right,and vice versa.
Connections to the MR-PRO consist ofoutputs on XLR-3M and RCA connectors at
the bottom, with a USB connector on theleft side and the DC power socket on theright. An XLR-3F at the front of the case isprovided for cable testing.

TGenerationThe Minirator is more than just a signal
generator providing a very useful range ofreference signals for testing andtroubleshooting audio systems. It also
serves as a test instrument, with functions
for testing cables, phantom power andimpedance. The output connectors provide
what NTI call ‘True Level’ balanced signals,
where the output corresponds to the set
source voltage over a wide range of loads.
The unit is switched on via the On/Off
button, and once the unit is powered up a
short press on this button will toggle thedisplay backlighting. Most of the time theunlit display will be clear enough to readunder ambient lighting, and this willconserve the batteries, of course. A lowbattery condition isindicated by a battery
icon appearing at thetop right of the LCD
display.
The screen display
is clearly laid out andinformative and isdivided into three
sections: the menu bar,
the test signals, and themeasurement values.
The menu bar isdivided in two with theleft side selecting thesignal generator, cable
tester and system
functions, while theright side sets theconfiguration and provides access to ten
memory locations for storing or recallinguser-settings.
With the Generator mode selected,pressing the Wave button brings up a submenu with eight test signals – more on thatin a moment. The Cable Test mode puts theMR-PRO into measurement mode, while theSystem mode calls up the settings for thepower save and backlight functions, as well
as displaying the current firmware version
and unit serial number.

“The Minirator
is more thanjust a signalgenerator”
The test signal window features ‘lvl’ (foroutput level) and ‘f’ (frequency) readouts.
These are selected either via the navigation
wheel or directly via the Level and Freq
buttons, which then highlight the chosenparameter. The values are set by turning therotary wheel. The Sens (sensitivity) button
displays the increments available which canbe selected by turning the rotary wheel
while holding down the Sens button. Theincrements vary with different test signals,

and taking the first test signal (sine wave) as
an example the frequency can be varied inthird, sixth or twelfth octave steps or in
1Hz increments. Personally, I find the term
‘sensitivity’ a misnomer here; ‘resolution’would be clearer.
The sine wave signal output can be
adjusted over a wide range of static levels
and frequencies, while the sweep mode
provides a stepped frequency sequencespanning a selectable range with aresolution of up to 1/12th octave. The
frequency start/end points can be adjusted
between 10Hz and 20kHz, and the durationof each step can also be set between 0.5
and five seconds. Sweeps may be once-onlyor continuous, with the time of the trigger
between sweeps also being adjustable up toten seconds. The sweep tone starts with a
1kHz signal that then drops to the starting
frequency of the sweep, and ends with adrop back to the starting frequency.
The Chirp function provides acontinuously variable signal used for
frequency response measurements, impulse
responses and the acoustic assessment ofrooms. Linear and logarithmic options areprovided and the frequency and timing
parameters are fully adjustable. A variationof the Chirp signal is the Delay Test mode
which is intended for use with NTI’s‘Acoustilyzer’ measurement unit, and allows
delay times to be measured.
The Pink Noise function provides noisewith a 20kHz bandwidth which can beswitched to run continuously orLINE UP June/July 200821

“Most of us
have cable
testers but NTI
takes this one
step further”

intermittently (with adjustable cycle times).
A White Noise function is also provided foruse with FFT measurements. The Polarity
test signal is a sawtooth waveform forchecking the polarity of equipment andloudspeakers in conjunction with the‘Minilyzer’ or ‘Acoustilyzer’ devices.
Unusually, there is also a File mode
which allows the user to select test
sequences in Wave file format. NTI
provides a selection of demo files including
messages and musical excerpts, and thesecan be replaced via the USB link to acomputer. The MR-PRO’s memory capacity
is 32MB. Various alternative files areavailable on the NTI website, one of themost useful being pink noise in separate
third octave bands.

Measuring
In Sinewave mode, the MR-PRO will alsomeasure input impedances and the balance(or imbalance! ) within a system. I tested
the three microphone inputs on my DJ
mixer that I use at home and found to mygreat surprise that these are unbalanced!
This is a pitfall that is more common than
one thinks; an XLR connector doesn’t
always mean ‘balanced’. The display at thebottom of the screen shows the balance
situation between pins 2 and 3 both

NTI MR-PRO
Price: £246.94
Cable Test Plug: £19.59
www.nti-audio.com
Bryant Broadcast
Tel: +44 (0)20 8404 4050
www.bryant-broadcast.co.uk
Canford Audio
Tel: +44 (0)19 1418 1122
www.canford.co.uk

22 LINE UP June/July 2008

graphically and numerically. Operationally,a minimum signal level is required for thisfunction and I found that -10dBu was about
as low as you would want to go. This facility
is excellent for testing for faults such as
short circuits, defective cabling andcontinuity in presumed balanced systems.
The same screen also shows thephantom power voltage (or DC 0.0V whenno phantom power is present). Connecting
the MD-PRO to an input with phantom
power, the DC voltage is displayed, and if
there are unequal voltages on each pin the
DC icon will blink. Selecting the icon with
the Enter button will show the faulty
voltage source.
Most of us have cable testers but NTI
takes this one step further, the test being
based on impedance measurements with
dissimilar load impedances to ground fromeach leg (1k ohm for pin 2 and 2k ohm forpin 3.) This arrangement enables the unit towork out the nature of any faulty cable. Totest cables, you select Cable Test from themenu and plug the cable underinvestigation into the XLR sockets on theunit. If the cable is open circuit the screen
displays ‘No XLR Cable.’ If the cable isdefective in some way the screen displays‘Defective’ and indicates the impedancespresent on pins 2 and 3 for easy

identification. If the cable is good, thescreen displays ‘OK XLR connected 1:1.’
Testing loose cables is no problem but what
about long and/or installed systems? Theanswer here is to get the optional ‘Cable
Test Plug’ from NTI and plug it in at the far
end of the cable under test. Works a treat!
The USB connection provides an easy
way to get firmware updates for theMR-PRO and to load and unload Wave files(mono and stereo). However, it only works
on Microsoft operating systems (Windows2000 and later).

Conclusion
The NTI Minirator MR-PRO proved itself
extremely useful in the field, and a detailed
investigation has shown that it has a lot ofpossibilities. On that basis, I would
recommend it as a ‘must have’ item for yourtest kit. Used in conjunction with the other
NTI instruments, the scope formeasurement widens considerably, but as astand-alone unit it remains a vital ingredient.
Highly recommended.