ng from behind the listener." (Stach 1998)
             Microphone directionality can be accomplished by using a single microphone with two sound inlets. In this mechanical method, the time lag created by a sound entering each inlet is precisely calibrated to cancel out sounds from the sides and back of the microphone as they strike the diaphragm. The Phonak MicroZoom uses an electronic approach. Each MicroZoom contains two omnidirectional microphones. According to the flyer, "One picks up sound in front of you while a second picks up sound from the sides and rear. A tiny computer chip inside the aid analyzes both sounds. It then enhances the sound from the front, and reduces background sounds from the sides and rear." (Phonak 1997) In reality, the "tiny computer" is analyzing the time it takes for a sound to reach each microphone and mathematically decreasing ALL sounds from the sides and rear, speech included.
             Directional microphone technology is fallible in one regard: it assumes that all "noise" is spatially related. Unfortunately, much of the noise present in our environment is omnidirectional. Even though significant benefit can be achieved by "sound focusing", a directional aid also must perform in an environment with multiple speakers situated around a listener, combined with noise from high priority directions.
             Signal processing, or digital signal processing (DSP), is partly utilized in amplification in order to narrow the focus from "all" sounds to "speech" sounds. A linear aid will amplify all frequencies equally, limited to the characteristics of the input output transducers and the coupler type. On the other hand DSP aids can alter the frequency response of an aid based on their design and/or programming. There are many techniques that can be used which are based on type of loss, but since speech encompasses such a wide frequenc...