Jeffrey Harris, a contributor to Pro Audio Review, is an independent producer/engineer. He also teaches at the Conservatory of Recording Arts and Sciences.
Acoustisoft's ETF program is an inexpensive and powerful PC-based acoustic analysis tool for evaluating recording studio control rooms, home theaters and other small-to-medium acoustic spaces. ETF 5.42 is for Windows platforms and PC emulators on the Mac.
Product Points
Applications:Test software
Key Features:Acoustic analysis software tool for PC-compatible systems; automatic setup and calibration; provides room design solutions
ETF stands for Energy, Time and Frequency. My old Version 3.0 ETF software served me well in the design of several recording facilities. The even more comprehensive Version 5.42, is my new primary reference tool.
Features
Version 5.42 is more than a software revision - it is a new approach to data acquisition. In early versions of ETF, the necessary impulse signal was provided on a CD for playback through a speaker that was picked up by an instrumentation microphone in the room. The received transient measurement pulse then needed to be recorded into the computer as a WAV file for 3 minutes to provide good background noise immunity. This file was then opened in the ETF software for analysis. All this took several minutes before you could see any results. Considering the $129 price of the Version 3.0 system, this was a fair trade-off.
Version 5.42 ($149.95) uses a test signal known as Maximum Length Sequence (MLS). It differs from the impulse signal previously used. MLS is a stream of pulses resembling white noise that is produced by the software and sent to an amplifier and speaker in the room under test.
The MLS test signal burst of about 8 seconds is enough to energize the room for very accurate results. The software then converts this into an equivalent impulse response.
As in earlier versions, a PC with a duplex audio card, an omni microphone and preamplifier are all that is needed to make useful measurements.
The ability to utilize inexpensive audio cards is achieved by using a two-channel mode. This setup places a reference signal in the left input and the microphone preamp output in the right side. The software then corrects for hardware phase and amplitude anomalies.
With ETF 5.42, near-real-time acoustic analysis becomes affordable. From the Acoustisoft Web site, one downloads a working demo and then buys the six-digit license number for full operation.
A calibrated German-made microphone and preamp are also available from Acoustisoft for $249.95. I used this combination and the downloadable Version 5.42 of the software for my tests.
In use
After printing out the User Guide, I set up the system in a new control room at my facility. The user interface differs enough from my earlier version, with new icons and page layout, that a quick read of the guide was in order.
I was pleased to see a logical series of icons that led me through system calibration and first measurements.
The data-gathering window opens with a Level Check button that verifies both microphone level and the calibration reference. Next is the mixer function, which allows for adjustment. Start Test gets down to the business of gathering data. Within 10 seconds the Measurement Result Window displays impulse response for the first 20 milliseconds. That is fast!
The data is now available for display as linear-frequency response, low-frequency response (with adjustable gate times - great for room modal resonance), RT60, logarithmic-frequency response, loudspeaker phase, cumulative spectral display and mic/speaker distance.
The new displays lacked the old waterfall 3D look of earlier versions. The new interface's graphic overlay method, however, makes it easy to identify room modal resonances by acquiring and analyzing different location measurements. Also included is a Sequential Data Acquisition mode to allow for rapid updating and display of change in the acoustical space.
The early results were exactly like what I observed with Version 3.0, but much faster!
With all this analytical capability, you will probably find something in the tested space that you want to change, and you do not have to go far for a solution. Right there under the File pull-down menu is Device Designer, a very cool program for calculating and building both Helmholtz resonators and quadratic residue diffusers.
Summary
If you have any interest in experimenting with acoustics and cannot afford some of the other testing options, then Acoustisoft's ETF is worth your consideration.
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