自动定向话筒

　　简介

　　半导体自适应定向传声器（ADM）算法是一二麦克风处理方案助听器。它的目的是自动减少源于后面或从配戴助听器的一侧不影响声音前面。该算法实现了连续调整麦克风极性图案中的空白最小化ADM输出端的噪声电平（见图1）。所需信号与噪声完全基于到达方向的尊重致助听器。前半球的声音是通过无衰减，而声音从后面来半球被认为是噪音和减少。这个传声器极性图案中零的角位置在90到180度范围内连续可变0度代表前面。

　　The location of the null in the microphone pattern is influenced by the nature of the acoustic signals （i.e.， spectral content and direction of arrival） as well as the acoustical characteristics of the room. The ADM algorithm steers a single， broadband null to a location that minimizes the output noise power. If a specific noise signal has frequency components that are dominant， they will have a larger influence on the null location than a weaker signal at a different location. In addition， the position of the null is affected by acoustic reflections. The presence of an acoustic reflection may cause a noise source to appear as if it originates at a location other than the source location. In this case， the ADM algorithm will choose a compromise null location that minimizes the level of noise at the ADM output. Figure 2 shows a screen shot of the Interactive Data Sheet （IDS） with the Adaptive Directional Microphone front end mode selected. Figure 3 shows IDS with ADM mode disabled.

　　The ADM as it was implemented on Inspiria Ultimate， the GA3285， also has an Auto mode. In this mode， when the ambient sound level is above a threshold of approximately 55dBSPL and the polar pattern has adapted to something other than omni-directional， then the adaptive polar pattern is enabled. If the polar pattern adapts to omni-directional， then the algorithm will switch to single microphone， omni-directional mode to reduce current consumption.