ETF, or How I Learned to Love My Equalizer
By Kalman Rubinson   •   July, 1998 Because I'm suspicious of just twiddling knobs to make the sound "nice," I didn't rely solely on my ears when I used the Z-Systems rdp-1 that I review elsewhere in this issue for speaker and room contouring. Instead, I used the ETF speaker/room-analysis software from Acoustisoft to help me manipulate the equalizer properly. This program can measure the first-arrival, on-axis speaker response, as well as the room response with its early and late reflections and its resonances.

Without the visual and objective feedback that ETF provides, each adjustment would have required extended listening sessions with diverse program material for assessment. Using ETF, I knew exactly the effect on the initial response and how room response reshaped it. With a tool as precise and powerful as the RDP-1, ETF (or another analysis tool) is almost essential to the preservation of sanity.

ETF runs under Windows 95/NT and requires a PC with soundcard and a microphone. (A calibrated microphone is preferred; one can be purchased from ETF.) The user plays a series of calibrated test signals (pre-emphasized pulses) through the system under test, records the response with the microphone at the listening (or other) position, and analyzes them with ETF. The resulting displays show the frequency response of the speaker (early response), and the later responses as filtered through the room acoustics. The displays can be stored, compared, and/or printed.

ETF provides RT-60 reverberation evaluation, bandwidth-limited and time-gated displays, and statistical correlation between your room/system reverberation and an ideal diffuse reverberant decay. It can also measure THD in subwoofers and loudspeakers, guide in the placement of speakers for stereo and home theater applications, and assist in the design and construction of Helmholtz resonators and QRD diffusers for room correction. There are extensive Help files, and the price includes free upgrades for a year. This last is important; the designer, Doug Plumb, has upgraded the software substantially in the past year, and each new version (now at v4.0) includes welcome functional and interface enhancements. In fact, Plumb's rapid upgrades have outpaced my ability to conduct a formal review, so don't hold your breath.

ETF v4.0 is available for $199.95 from ETF, Oshawa, Ontario, Canada L1J 5M4. Order desk: (800) 301-1423 or from Acoustisoft.