I love neat gadgets; so, when the Neutrik Minirator MR1 was introduced at the Fall 1998 AES show, it was love at first sight. This pocket-sized audio signal generator went directly into my field tool kit, and another one divides its time between my workbench and home studio. Nine years later, the Minirator has been completely redesigned, and a significant update it is. Now there are two models: the MR2 and MR-PRO. I reviewed the more fully featured, $525 MR-PRO, but I’ll detail the differences between the models as this review goes along. Features
The Minirator resides in a new instrument package, with a complete front panel facelift, — including a larger, more informative and easier to read LCD, a scroll wheel and Enter button replacing the Mode and Cursor buttons, and quick access buttons to the waveform selection, level and frequency adjustments. New on the front panel are an Esc key to back out of the current selection, an illuminated Mute button to turn off the output, and a control to select the adjustment increments for frequency (1/3, 1/6, 1/12 octave or units of the least significant digit displayed) and level (0.1 or 1.0 dB). The Power button doubles as a display backlight switch.
Gone from the original design is the wonky swing-out male XLR output connector. It’s been replaced by a solid, locking, recessed XLR (bless ’em). The unbalanced output RCA jack seems to fit most plugs better than the MR1. The MR-PRO has a female XLR connector, which is used with its Cable Test function. A USB port is provided for firmware upgrades and for uploading WAV files to the PRO’s file player.
Power is from three AA cells with expected battery life of about 10 hours for the MR-PRO and 20 hours for the MR2. An external power socket is provided (5-8 VDC), and a wall-wart adapter is available as an accessory. Finally, the MR-PRO comes equipped with a spiffy blue flexible synthetic bootie to protect it against shock.
One major improvement over the MR1 is an increase in maximum output level. When the MR1 was introduced, we were still working largely in an analog world and a +4 dBu test signal was sufficient for most applications. With a maximum sine wave output level of +6 dBu, the MR1 filled the bill. In the digital world – with headroom being essentially at the discretion of the user – we frequently want to test a device near its maximum operating level, and +6 dBu only gets the meters up to about half scale. The MR PRO’s maximum sine wave output is +18 dBu; the MR2 maximum output is lower, at +8 dBu.
The MR-PRO offers a unique and powerful function: the ability to load, play and continuously loop a 16-bit/48-kHz audio WAV file. The latest firmware version accommodates both mono and stereo files, playing back the mono sum of both stereo channels. The file-playing capability allows you to create and use specialized test waveforms or sequences. A few examples are pre-loaded, including a speech intelligibility test sequence (to go along with the STI-PA function in NTI’s AL-1 Acoustilyzer), several musical instrument sounds and voice announcements. (For example, “The following test sequence helps our specialists to optimize the PA system. Thank you for your understanding.”) The NTI web site offers a collection of useful waveform files for downloading, or you can make your own.
You can store the current setup in any one of 10 presets for instant recall. You’ll personally need a good memory, though, as they’re all named Config_(0-9) and there’s no means of renaming them to remind you of what you’ve stored. (Just for kicks, I stored a 440 Hz +4 dBu sine wave in one location as an instrument tuner.)
Minirator is the name, and generating signals is the game. The waveform menu includes sine, pink and white noise, sweep (stepped), chirp (essentially a continuous sweep, either linear or logarithmic), plus Delay and Polarity (a couple of specialized waveforms that go along with tests built into NTI’s Acoustilyzer and Minilyzer). Square waves are conspicuous by their absence. I like to run a square wave through a device and look at its output with an oscilloscope as a quick check for ringing or loss of high or low frequency response, so I inquired about their whereabouts. Tom Mintner, President of NTI Americas, offered a reasonable explanation.
While the MR1’s square wave output was useful, it wasn’t perfect (I refreshed my memory — it does indeed ring quite a bit). It’s really better, though more expensive in a digital-based product, to generate a square wave with hardware than to synthesize it digitally. NTI decided that rather than add expensive dedicated hardware circuitry used only to generate a square wave, users who wanted square waves (or square pulses of various duty cycles) could add their own using the wave file player feature. (According to Mintner, NTI already offers not only square waves, but other free MR-PRO signals such as band-limited noise, for download at www.nti-audio.com. – Ed.
I usually use only 100 Hz and 1 kHz square waves, so I’m a happy camper using the file player. MR2 users, however, will miss out since file playback is unique to the MR-PRO.
Measurement functions (unique to the MR-PRO) are load impedance, balance (impedance difference between pins 1-2 and 1-3) and phantom powering voltage. Impedance is read directly, with an open or near-open circuit indicating “>50kø.” Placing the cursor over either the DC or RL (load impedance) label displays the voltage or resistance between pins 1-2 and 1-3 independently, an aid to diagnosing a defective cable or dodgy phantom power supply.
The MR-PRO’s Cable Test function utilizes resistance measurements to verify the integrity of a cable plugged either between the two XLR connectors on the unit or connected to the MR-PRO outputs and terminated with a test plug. In the Cable Test mode, it looks for specific resistances – 1 kilohm between pins 1-2 and 2 kilohms between pins 1-3. If it’s happy with what it sees, OK is displayed. A cable with either lead or the shield open or with pins 2-3 reversed will display “DEFECTIVE” and the two resistance readings will be displayed (pin 1 open reads 1.5 kilohms for each leg), guiding you to the problem.
Field and bench test and service, troubleshooting in the studio, PA, or installed sound
Good variety of very high quality test signals as well as other useful performance checks and measurements. Compact, easy to operate, rugged
NTI Americas Inc. | 503-684-7050 | www.nti-audio.com
There really isn’t much to say other than that everything worked just as expected, and that’s a good thing. Operation was intuitive – other than learning how to interpret resistance readings, update the firmware, and load WAV files, you’d hardly have to crack the manual. I had fun checking the input impedance of every mic preamp in the studio.
I had only one small quibble: that the resistance readings displayed for a faulty cable could be confusing. More than once when measuring a cable with pins 2 and 3 reversed, I saw 0.98 kilohm and it didn’t register with me that this is nearly 1 kilohm, the correct value but on the wrong pin. If it was rounded to 1 decimal place it would have read 1.0 kilohm, giving a clear indication of the nature of the fault. I could blame it on senility, but it could work better.
While I realize the limitations of battery-powered equipment, I wish they could have squeezed a couple more dB out of it. Many contemporary A/D converters require an input of +20 dBu or even a bit more in order to reach digital full scale, so even the MR-PRO won’t always make the Overload light come on.
Another wish is that the frequency range extended beyond 20 kHz. Since much of today’s digital work is done at 96 kHz sample rate and higher, arguments as to whether we can hear it or not withstanding, it’s reasonable to test at least out to 35 kHz. Summary
The MR-PRO does what it claims, and it does it very well. The compact size and shock protection make it ideal for the field kit, and the accuracy, precision, and low distortion of the signals it generates make it equally home in the lab or service bench.
Now for the hard part: at a bit over $500 on the street — there isn’t a big dealer margin on this sort of gear — it’s not going to be for everyone, though everyone who works with audio gear really should have some test gear. The MR2 at $325 is a little gentler on the wallet, but it’s not the bargain that the original MR1 was at its initial price of $139 (though it eventually crept up over $200). Blame inflation or the weak dollar, but do give it some consideration. Good test equipment can answer a lot of questions about your gear and help you to find problems when they occur.