I enjoy audio and acoustical tests and measurements. So, at the 131st AES Convention recently held in New York, it was fun hanging out with some of my audio friends and colleagues and finding out not only what projects they were working on, but what test and measurement apps were on their mobile devices.
One of these friends, Peter Mapp, principal of Peter Mapp + Associates, a specialist acoustic consultancy in Colchester, Essex, U.K., delivered one of the AES "Hot Lunch" presentations, a 45-minute talk on this very topic.
It's truly amazing the extent of available measurement tools that literally fit in the palm of a hand. Are there limitations? Sure. But if understood, these tools are great for many of the field measurements we need to make; for quick checks; and to determine whether other test gear needs to be brought in for a job.
STUDIO SIX DIGITAL LLC
One of the more popular apps, based on an unscientific survey of my audio friends at the AES convention, seems to be Audio Tools from Studio Six Digital LLC. This is a suite of audio and acoustical test and measurement app modules for the Apple iPhone, iPad, and iPod touch.
Peter Mapp holds his Apple iPad running the SPL Dashboard app by Studio Six Digital, a series of four sound level (SPL) measurement displays. Photo by Mary Gruszka Andrew Smith, technology director of Studio Six Digital, is no stranger to audio test and measurement. He founded TerraSonde, the maker of the AudioToolbox range of analyzers.
The basic Audio Tools suite ($19.99 as of October 2011) includes a sound pressure level (SPL) meter; an SPL Dashboard for the iPad, which puts all purchased SPL modules on one screen; a real-time analyzer (RTA); a dual-trace audio scope with triggering and single sweep capture; delay finder to find the signal delay between loudspeakers; signal generator; surround sound generator; monitor for the mic or line input; file upload capability; a calculator designed for audio and acoustical work (includes dB, SPL, sine wave, reactance, room modes, Ohm's law, delay and bandwidth); and a recorder.
If the basic suite isn't enough, the user can add modules for additional fees. Most range from $2.99 to $19.99, with specialty modules higher.
The SPL module can be enhanced with SPL Pro, SPL graph, and SPL traffic light. Additional acoustic analysis modules include FFT (fast Fourier transform), ETC (energy time curve), impulse response, and Smaart Tools. The latter two modules are two of the higher priced modules.
Smaart Tools sound system measurement, optimization and control software is licensed from Rational Acoustics, who makes this program for the PC or Mac.
Additional line input modules for Audio Tools include VU/Peak meter, THD+n (total harmonic distortion plus noise), amplitude sweep, and a phase meter.
Additional speaker test modules include a polarity tester for loudspeakers; a distortion driver; an enhanced impedance meter; and the latest standard (version 4) for speech intelligibility index (STI-PA). The latter is the most expensive module at $299.99 due to the various royalty fees, according to Smith.
John Siau shows his Android-based smartphone running the Speedy Spectrum Analyzer app. Photo by Mary Gruszka As Mapp pointed out in his presentation, STI is a sophisticated measurement and for the measurements to be accurate, the user must use an external interface box.
Conveniently, Studio Six Digital offers such an interface box—the new iAudioInterface2, which was shown at the AES convention. This battery-powered digital interface for the iPhone 4, iPod touch 4, and iPad includes a phantom-powered mic input, balanced line input, balanced line and headphone output, and a Toslink optical digital audio output.
Mapp, in his AES presentation, also showed some of the audio and acoustical test apps for the iPhone, iPad, and iPod touch from Faber Acoustical. These include IOScope ($149.99), SignalScope Pro ($74.99), SignalScope, SignalSuite, SoundMeter, SpeakerDraft, and dB.
SignalScope Pro includes an FFT analyzer, octave-band analyzer, sound level meter, oscilloscope, and stereo signal generator. SignalSuite is a signal generator, and SpeakerDraft helps loudspeaker low-frequency response. The dB module can record an image overlayed with a display of the sound level.
FOR SMARTPHONES, TOO
Do you prefer smartphones running on the Android operating system? There are audio test and measurement apps for you, too.
iSTI from Embedded Acoustics (L), a professional STI (speech transmission index) measurement app and SPL Dashboard, an app by Studio Six Digital, a series of four sound level (SPL) measurement displays. Kurt Graffy, a principal consultant with Arup Acoustics in San Francisco, showed me the Audio Tool suite by jjbunn (Bofinit Corp.). This set of modules includes a real-time spectrum analyzer; SPL meter; spectrogram; chart recorder; signal generator; loudspeaker polarity checker; data file storage capability; decibel meter; noise criterion curves; chart recorder; and reverberation time measurements.
Studio Six Digital, working with AudioControl, provides SPL Meter app with characteristics found on analog SPL meters including ballistics, ranges, filters and decay rates.
Smith from Studio Six Digital said, "We have a great relationship with AudioControl. They are handling both the Android development (as it grows), and they are warehousing our hardware and acting as our master distributor. We see more synergistic things in the future."
BACK TO THE SHOW
After listening to presentations on grounding and shielding and hums and buzzes, by Bill Whitlock from Jensen Transformers of Chatsworth, Calif., it became clear that we need a gauss meter in our audio tool kits to see if external magnetic fields are causing problems in our systems.
John Siau of Benchmark Media Systems in Syracuse, N.Y., attended one of these sessions and showed us the Metaloid Field Detector from jjbunn (Bofinit Corp.) on his Android-based smartphone. This app uses the smartphone's built-in magnetometer to measure magnetic fields. Siau said the readings on his smartphone track well with his hardware gauss meter.
Siau also showed me the Speedy Spectrum Analyzer and FFT from Electron Chaos, and Perfect Pitch guitar tuner, both for Android-based phones.
This gives only a brief idea of all the capabilities of the apps mentioned and even of all the audio test and measurement apps that are available.
There are some things to watch out for when doing measurements on mobile smart devices, which will be discussed in a future column.
Mary C. Gruszka is a systems design engineer, project manager, consultant and writer based in the New York metro area. She can be reached via TV Technology.
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