Audio test and measurement have come a long way in the last 15 years. It wasn’t all that long ago that dedicated measurement hardware was still the only realistic option for critical measurement work. As personal computers and laptops became more prevalent in the audio field, measurement came within reach of virtually any working engineer. The inevitable evolution of this trend is for smart phones and tablets to perform the same measurement tasks that required a high-end laptop only five years ago.
Studio Six Digital has been on the forefront of iOS test and measurement since the very earliest days of third party app development for the platform. Studio Six now has the definitive test and measurement platform for iOS devices. In addition to an extensive suite of audio applications for iOS, Studio Six Digital also has an audio interface and a lightning connector based measurement microphone called the iTestMic2, which is the subject of this review.
At First Glance
Upon receiving my demo iTestMic2, I unboxed it and looked closely at the microphone and the remaining contents in the package. The packaging itself was nothing to write home about, although the labeling on the outside of the box was useful, listing some basic features, specifications, and most importantly, showing which iOS devices the iTestMic2 is compatible with. The microphone itself looks like a typical measurement microphone in this price range, with a half-inch diameter capsule that fits in a standard calibrator. The mic came with a small certificate stating that it had been calibrated to 94dB by a B&K 4231 and was compliant to ANSI S1.4 Type 2 specifications for sound level metering. I thought the inclusion of the certificate was a nice touch for a microphone in this price range, and it instilled confidence that it was professional quality product. The iTestMic2 is relatively small and lightweight, especially considering that it has a preamp, analog to digital converter, digital to analog converter and power supply built in. The mic certainly does not feel robust like an Earthworks M30, but that’s not what this mic is intended to be, so it’s probably not a fair comparison.
I knew very little about the mic before opening the box, so there were a few things that had me confused when I first examined it closely. Unlike a typical measurement microphone with an XLR audio connector, the iTestMic2 has a lightning cable and connector for direct connection to an iOS device. That part was straightforward and expected. On the bottom of the microphone there is an 1/8-inch audio jack and a DC power input. I immediately became concerned that the mic was going to require an external DC power supply for basic operation, rather than being powered by the iOS device itself. After some additional research, it turns out that the DC input is for charging the iOS device while using the microphone, which is a very handy feature. Because iOS devices rely on a single lightning connector for charging and connection of external audio devices, the DC input is necessary if you want to charge the device while taking measurements. If you don’t need to charge your iOS device while using the mic, it can be powered solely by the iOS device. Directly next to the DC input is an 1/8-inch audio jack. Again, at first I was somewhat perplexed, but as it turns out, the mic provides the 1/8-inch jack as an audio line output, another useful feature. Current iOS models also rely on the lightning connector for audio output, which happens to be the bane of many people’s existence. Fortunately, the iTestMic2 solves this problem by allowing for audio output from the bottom of the mic. The nature of the iTestMic2’s lightning connection dictates that it will always be used near the iOS device it is being used with, so having the 1/8-inch audio output on the mic itself makes sense in this case.
Anyone who is serious about audio test and measurement would wonder about the specifications of a mic with a lightning connector. It’s just so different than what people are used to with a measurement microphone, how could you not have questions about it? The good news is that the iTestMic2 complies with the ANSI S1.4 Type 2 standard for Sound Level Meters. As mentioned earlier, the microphone’s SPL is calibrated at the factory, and the calibration is stored in the microphone itself. In addition, every iTestMic2 has its own frequency calibration file that compensates for capsule variations and helps flatten the microphone’s response. Interestingly, the frequency calibration is stored in the cloud and can be retrieved within the Audio Tools application (more on Audio Tools below). Studio Six Digital’s cloud server identifies the microphone by its serial number, downloads and stores the frequency calibration for repeated use on the iOS device, so the download is only required on first use. Studio Six lists the frequency response spec of the microphone as 20Hz-20kHz +/-3dB.
The Apps
Studio Six Digital has been developing its suite of applications, collectively called “Audio Tools,” for nine years. That dates these applications all the way back to the very first iPhone, which demonstrates Studio Six’s commitment to their app development. They have stood the test of time. As a result, the suite of applications is a very well developed and full-featured set of audio test and measurement tools. If there is a more in depth assembly of audio measurement tools for iOS on the market, they have yet to come to my attention.
Audio Tools can be purchased from the Apple App Store for $19.99. That’s not an inexpensive application by any means, in fact it is one of the most expensive apps I have on my device, but it’s well worth it and gets used regularly in the field. The core Audio Tools application includes every day, useful functionality such as an SPL meter, an RTA, a surprisingly fully-feature and high quality FFT Analyzer, a Line Input Tester, an Audio Scope (Oscilloscope) and even an audio recorder. In addition to the test and measurement tools listed above, there is also a section of handy design tools compliments of Pat Brown at SynAudCon. The design tools, included in the base Audio Tools application contain a CLF (Common Loudspeaker Format) viewer with a database of over 500 speakers, an amplifier calculator, a microphone spacing tool and much more. I suspect that even people who already own Audio Tools don’t realize how much functionality comes included with the base application.
Going beyond the base Audio Tools application, Studio Six uses an in-app purchasing model for the rest of their more advanced applications. There are a lot of them, and they are group into several logical sections discussed below.
SPL Modules
Audio Tools includes a basic SPL meter that is sufficient for quick, accurate measurements. In addition to what is included, there are several addition modules that can be added to provide more advanced SPL measurement and monitoring. First, there’s SPL Pro, which adds ANSI/ISO slow, fast, impulse and peak modes and of course has A and C weightings. I found SPL Pro to be accurate when compared with other SPL meters I own, and aside from a fully featured measurement software costing hundreds of dollars, it’s probably one of the best SPL meters available at this price point.
Beyond basic SPL measurements, there is an SPL graphing application that allows SPL measurements to be graphed (and optionally recorded) for up to a 24-hour period. This would be useful for long term monitoring of SPL at an outdoor concert or festival. In addition, there are SPL traffic light apps that show red, yellow and green at user defined SPL levels, which is a great visual way to know exactly where your mix is sitting SPL wise.
Acoustic Analysis Modules
Included in the base Audio Tools application are a very nice RTA and a well-appointed FFT Analyzer. In addition, several more advanced acoustical analysis modules can be added via in app purchases. For example, there is an ETC (Energy Time Curve) app for plotting decay times and RT60, an Impulse Response app for recording and analyzing impulses, a Transfer Function app that allows for true dual channel transfer functions with phase and magnitude displays, a LARSA app for loudspeaker analysis and a Spectral Balance app. Finally, there’s a SMAART Tools add-on application that provides single channel measurements using the most popular audio measurement software on the market from Rational Acoustics. Overall, the acoustical analysis package is as full featured as anything I’ve seen on any device.
Line Input and Speaker Test Modules
Audio Tools has so many individual modules that it’s impossible to cover them all in this article. Each group of applications is worthy of its own in-depth review. In addition to the in-app purchase modules discussed above, Audio Tools also has extensive Line Input testing such as VU Metering and Total Harmonic Distortion, as well as Speaker Tests such as Polarity, Distortion and advanced Speech Intelligibility (STIPA).
If you already own a measurement microphone but you like the convenience of iOS based audio measurement, Studio Six Digital also makes an iOS audio interface specifically designed for use with Audio Tools called the iAudioInterface2. It provides true dual-channel FFT measurement capabilities, a phantom powered mic input, line input and output and much more.
At a Glance
From Laptop to iPad/iPhone
I found the iTestMic2 and the Audio Tools applications to be first class tools for audio test and measurement. The convenience of having these tools on an iPhone or iPad is unparalleled, and is a natural evolution of laptop-based measurement. If you’re in the market for measurement hardware or software, I recommend you consider Studio Six Digital before making any decisions.
iTestMic2
PROS: Affordable and convenient audio measurement for iOS, Pre-calibrated from the factory. Calibration can be updated by the user, Meets ANSI Type 2 specifications for frequency, level and directional characteristics
CONS: Measurement mic must be near the iOS device running Audio Tools application, Cost of in-app purchases really adds up if you require many different modules.
STATS
- Mic Size: ½” diameter capsule
- Gain Ranges: 2 (to support 25-120dBA SPL range)
- MSRP: $229
- Manufacturer: Studio Six Digital
- More Info: www.studiosixdigital.com
