"Why Do I NEED the Real-Time Composite Signal?"

by Larry Revit, hearing scientist

Although the following may sound more like an advertising supplement than an applications bulletin, there is an important issue to discuss: why the Fonix Real-Time Composite signal is a must for testing hearing aids in the nineties.

For Speed. The first reason is the unbeleivable speed of testing, speed that can free the tester from waiting around for a frequency sweep to finish. Nearly as fast as you can place your eyes on the display screen, the complete response curve has already been measured.

For Accuracy. In addition to sheer rapidity, high-speed testing carries important advantages. One of the requirements of accurate probe testing is that the test subject remain absolutely still and quiet. Trying to take a probe masurement with a swept tone or a swept band of noise is like trying to take a stop-action photograph with a slow shutter speed. Invariably, the subject moves; the results are blurred. Not so with the Fonix Real-Time Composite signal. Did you ever try to get a kid to sit still and quiet?

For Utility. Another advantage of speed: The ongoing real-time display is an interactive link with the customer's hearing aid. As you change the hearing-aid settings, whether in real-ear or chamber modes, you see the results, as the changes are made. This is especially useful when trying to match a real-ear response curve, or when demonstrating setting changes to a potential customer for a programmable hearing aid. (And the programmables will take over... NO DOUBT. It's time to be prepared.)

For Validity. Not only is the real-time composite signal fast, but it is right for testing hearing aids. To test how a hearing aid with signal processing (or even a linear hearing aid in saturation) performs in response to everyday inputs such as speech, you must use a broad-band signal such as the Fonix Real-Time Composite. Unlike swept-tone signals, the composite signal is not subject to the misleading result known as "the blooming effect. "1 The composite signal shows the true effect of signal processing. 2 And unlike swept-tone signals, the composite signal provides a clear indicator of a very nasty hearing-aid distortion called "intermodulation distortion." 3 (Intermodulation distortion can make voices sound garbled and harsh, especially the wearer's own voice!)

The industry's leaders know all that. That is why an ANSI standards committee is busy drafting a new American standard for testing hearing aids with broad-band, speech-shaped signals, ...such as the Fonix Real-Time Composite signal. Can the competitors promise that their equipment will be upgradable to meet the new standard? We can.

What's more, the very latest independent research on hearing-aid testing4 points up the fact that speech is often a combination of broad-band and narrow-band information, implying that the best way to evaluate hearing-aid performance thoroughly is to use both broad-band and narrow-band test signals? Do our competitors offer that choice? We do.

Speed, accuracy, utility, validity... All things considered, the Fonix Real-Time Composite signal let's you do a better fitting job in a shorter time. Be prepared for today's hearing-aid testing, with a Fonix Real-Time Analyzer. Don't get left back in the eighties.

Back to Larry's Corner Table of Contents

1 Heide J. Testing electroacoustic performance of ASP and nonlinear hearing aids. Hearing Journal, April 1987. Return.

2 Revit L.J. Testing ASP instruments with low-frequency input/gain and input/output curves. Hearing Journal, June 1989. Return.

3 Frye G.J. High-speed real-time hearing aid analysis. Hearing Journal, June 1986. Return

4 Stelmachowicz P.G., Lewis D.E., Seewld R.C., and Hawkins D.B. Complex and pure-tone signals in the evaluation of hearing-aid characteristics. Journal of Speech and Hearing Research, Vol. 33, No. 2, 1990. Return