Monday, May 25, 2015

Rode NTR - A New Bi-directional Active Ribbon Studio Mic

The Rode NTR ($799) is an active, bi-directional ribbon microphone that surpasses vintage designs primarily because of it's sensitivity (-30.5 dB re 1V/Pa (30mV @ 94dB SPL) ± 2dB @ 1kHz) and tone. In side by side comparisons with Rode's NT1 studio condenser mic, the NTR was 3 dB more sensitive. That surprised me!

Your father's or grandfather's ribbon microphone required so much mic preamp gain that increased noise floor was inevitable. How did they manage back then? Really good mic preamps, usually with a special transformer on the input to step up the voltage, and placement of the mic itself. Plus, early "hi-fi" systems didn't have anywhere near as much bandwidth as a 24-bit recording (or even an mp3). 

How much ribbon you are moving also figures into the formula. That can be achieved by the length of the ribbon or how many ribbons were used in one mic. The Beyer M160 and RCA 77 series ribbon mics grabbed some extra sensitivity by having two ribbons. Think about it. You basically have a relatively fragile strip of aluminum floating in a magnetic field. A sound happens, the ribbon moves sympathetically and that movement within the magnetic field generates a small voltage. 

A lot of "magic" was invested in the early ribbon mics. The thickness of the ribbon was and still is important. The Rode NTR ribbon has a thickness of 1.8 microns. 

Each ribbon is run through a crimping mill that imparts a pattern on the aluminum. The crimp is a "special recipe." This is done to provide the ribbon with some structure to strengthen it and allow it to be tensioned properly. 


Longer ribbons generate more voltage, but longer ribbons are more fragile. The ribbon must be stretched to achieve a linear frequency response. As any ribbon mic ages, the ribbon material will sag and change the response. According to Rode Marketing Manager Scott Emerton, "Our engineers spent a lot of time optimising the ‘crimp’ of the ribbon to minimise any slack being introduced. Also there’s a multi-stage tension and relaxing process for each ribbon as it’s placed in its motor which increases that life."

Addendum: Rode covers you with one new ribbon for free. They also warranty the NTR for a year and for ten years if you register the mic at www.rode.com/warranty.


Here's an image of the crimping and tensioning jig with a new ribbon spanning across the gap and held in place by the two brass blocks. For a motion picture of this procedure, here's a YouTube link. 


Equally special is the step up transformer that increases the sensitivity voltage. The video also shows the automated transformer winding apparatus and details. The final piece, in the case of the Rode NTR, is a low noise amp stage to provide more sensitivity. Rode sources the smaller circuit components, but Emerton says the bodies, electrics and transformers are made at Rode in Australia and the microphones are built there as well. 

Ribbons can have more mass than diaphragms on condenser microphones. That prevents them from picking up higher frequencies. Most ribbon mic have great bottoms, but there's not much going on over 10 kHz. The published response curve of the NTR shows a gentler slope than traditional ribbon mics and even shows a slight but very useful peak bump at 3 kHz and from there a slope to -10dB by 13 kHz. There is a return by 16 kHz. 


Having made that point, the NTR is not a bright sounding microphone, nor are most ribbons anyway. That means they're great for use on sound sources that have a tendency to be harsh, brittle or distorted. Flute, violin, guitar amplifiers, banjo and bag pipes come to mind. There are even some acoustic guitars that sound pretty nasty that will benefit from a ribbon mic like the NTR.

PROXIMITY EFFECT
Proximity Effect is the tendency for directional microphones of any sort to be more sensitive to lower frequencies the closer the microphone gets to them. How close you may be before being in the proximity effect field remains open to discussion. Is it a matter of inches or feet? To some degree it depends on the microphone. The ElectroVoice RE15 and RE20 dynamic microphones, for example, have reduced proximity effect because of the acoustic slit that compensates for being closer to the microphone. 

With the NTR and a rosewood body acoustic guitar, I found the proximity effect noticeable to begin to build at a distance of about two feet. You can probably get closer with a mahogany body acoustic guitar. The challenge is what to do with all of that low end. Fortunately, The NTR has enough sensitivity to allow for subtractive EQ to tailor the sound. In my studio, I had no trouble getting good levels at two feet, even while fingerpicking. If your space is noisy or has difficult acoustics, you may have some audible acoustic problems when trying to record that far away. My advice is to fix the acoustics of the space first. Then everything you do will sound better.



Here on the left is a video of a Martin Grand J-28LSE. It's a baritone guitar tuned four semitones (frets) below standard guitar tuning, so it sounds sort of HUGE. A lot of low frequency energy. If you get a mic too close to it, it won't sound very good.


As you watch and listen, you'll hear that using the neck joint position or being at least two feet back really improves the sound. Otherwise, you're in the Proximity Effect zone and the low end is overpowering.




This video on the right features the Rode NTR and a standard six-string acoustic guitar; in this case a rosewood Martin D28s with middlin' dead strings. Here I demonstrate the lobes and nulls of the Rode NTR and the horizontal and vertical mic orientation at the neck joint, sound hole and bridge.

The guitar is a bit woofy until you get at least a foot away. Of course, you can always reduce some of the low frequencies the EQ before or after you record. After shooting both of these clips, I began to really appreciate how well the NTR handles voice.


MY APOLOGIES. BLOGGER LAYOUTS AND COMPOSITION ARE VERY BUGGY. THIS BLOG IS MADE WITH BLOGGER AND I HAVE ONLY LIMITED AND ERRATIC CONTROL OVER LAYOUT. WHAT YOU SEE IS NEVER WHAT YOU GET! 

Where was I? Oh, right. The video above has three of my favorite tests for mics; Front-To-Back for directional mics, Hissing for phase anomalies and beaming and the Dreaded Key Jangle Test for seeing how well a mic handles transients. The Front-To-Back quickly tells you if your bi-directional mic sounds the same on each side. That's very important if you plan to use the mic for Mid/Side recording. Hissing is your own personal "white noise generator." If the mic has a beamy, uneven response, you can hear tonal changes as you rotate the mic. The Dreaded Key Jangle Test tells you how good the transient response of the mic is. Each in its own simple way reveals something about a microphone with absolutely no test gear. 


Last night we tried the Rode NTR out as a drum overhead three feet over the kit in a simple live to disc recording of a five piece group at a house concert. The space was a living room/dining room with a vaulted ceiling, wood floors and a stair well.

There was one small PA speaker on a stand and one floor monitor. The group consisted of electric bass, small drum kit, acoustic guitars with pickups, mandolin with pickup, acoustic piano and at least two vocals. Aiming the NTR face down from 3 feet above the drum kit meant it's nulls were left and right. The performers were positioned closely together. I was impressed by how little of everything else but the drum kit got into the Rode NTR. The side nulls were doing a great job. 

Where else do you use the NTR? I think it would do a nice job warming up a dulcimer, a small parlor acoustic guitar, Baby Taylors or even Martin Backpackers, especially when close miced. Guitar amps are also a logical choice.

I find a number of vocalists have a nasty little peak around 6kHz. If you can keep them from getting too far into the Proximity Effect woofy space, the Rode NTR can smooth them right out. I was impressed when I heard my own voice on the video playback of the clips that are part of this review. I used no EQ on them. It was the Rode NTR going right into my JVC HM650 camera. On small speakers, laptops and phones, the sound works just fine. On larger more critical monitors there's the unmistakeable low end density of a ribbon. A slight LF EQ adjustment there and the voice works very well and has a very natural and smooth quality. 

I'm a member of the local SAG-AFTRA Conservatory. The Conservatory gives workshops to local union members to help advance their craft. I recently gave a narration class and setup a Gefell M71 and the Rode NTR side by side. The NTR was several inches farther away. Here's SAG-AFTRA talent Sheila Blanc. If you like her read and would like to use her for VO work, she may be reached at: sheilablanctalent@gmail.com

Addendum: I did additive and subtractive EQ on each of her clips to taste.

IN CONCLUSION
The Rode NTR has enough sensitivity to allow for EQing, if needed. And if it weren't apparent from what I've said so far, you can minimize the amount of EQ needed by how close or how far away you position the mic from the source. That may require a "head change" if you've just been sticking a mic in front of a source, hitting the record button and trying to deal with EQing the sound during mixing. 

A lot has been written about the mic placement techniques of bi-directional ribbon mics. Once you wrap your head around the sacred geometry created by using bi-directional ribbon mics in a space and where you need to place musicians and instruments in that space, I suspect you'll be making some very good recordings with fewer microphones. 

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