本資料說明了反饋取消在最新數字助聽器中提供的功能對節奏的?R3920安森美半導體。反饋取消不同于其他反饋減少策略，因為它不減少前進正常工作條件下助聽器的增益。相反，該算法減少反饋通過制定

　　真助聽器反饋信號的內部估計然后減去這個估計從麥克風信號。如果內部估計是準確的，那么實際反饋被取消，助聽器不會尖叫。正確估計真正的助聽器反饋信號是必不可少的正確操作算法。由于反饋信號隨時間而變化算法必須對內部進行連續的調整模型，以確保外部反饋準確匹配。在半導體上的反饋消除器中，這些調整自動發生，不需要探針信號或其他用戶干預可能干擾助聽器的操作。最新的反饋消除算法安森美半導體新機制增加保持音頻質量的適應速度。這機制自動決定是否當前反饋條件需要大或小的調整內反饋?路徑模型。大調整用于快速消除聲反饋。當大不需要調整，選擇較小的調整最大化音頻質量。下面的部分描述反饋消除操作更詳細地強調影響反饋的因素檢測器的性能。文章的結論與可用于優化反饋的方法的討論檢測器的性能。這些方法允許用戶關于半導體數字放大器的增加產品性能。

　　PRINCIPLE OF OPERATION Adaptive Feedback Cancellation （AFC）， from ON Semiconductor， is a true feedback cancellation （also known as phase cancellation） algorithm. The algorithm operates by subtracting an internal estimate of the hearing-aid feedback signal from the microphone signal. The internal feedback signal is obtained by passing the hearing-aid output signal through an internal， feedback-path model. The feedback-path model in AFC is intended to match the impulse response， or time response， of the external feedback path. The feedback-path impulse response is the time signal that would be observed at the microphone output if an impulsive signal were produced by the hearing aid. As an example， the measured impulse response of a typical BTE hearing aid is shown in Figure 1?a. This plot shows an initial period of approximately 0.5 ? 0.75 ms with little or no energy. This time window corresponds to the analog-to-digital and digital-to-analog converter delays as well as any acoustic delays due to transducers， tubing， sound propagation through the air， etc. Following the initial delay is the main part of the feedback-path response which， in this example， persists for more than 2 ms. The net effect of the feedback canceller algorithm is to remove a certain portion of the feedback path impulse response. Since computational resources inside a hearing-aid signal processor are limited， only a portion of the total feedback path response can be cancelled. To achieve maximum effectiveness of the canceller， the cancelled part of the response should be that portion of the feedback path with the largest energy. This ensures that the net response has the lowest energy for the given length of canceller. For example， if the cancellation window is restricted to 1ms， then for the feedback path of Figure 1?a， the internal feedback model should look like the plot of Figure 1?b. When this is subtracted from the feedback?path response， the net feedback path is as shown in Figure 1?c. The corresponding frequency response is shown in Figure 2. This figure illustrates that the net effect of the feedback canceller in this example is to reduce the peak response of the feedback path by approximately 12 dB. Consequently， the feedback canceller in this example should provide approximately 12 dB of added stable gain （ASG） that is achieved without any impact on the forward gain of the hearing aid.