Two‐channel FFT techniques for measuring hearing aids with adaptive signal processing

Abstract

Hearing‐aid measurements made in test enclosures have traditionally utilized a sinusoidal method such as that of ANSI Standard S3.22‐1987. While this method works well with essentially linear aids, it gives misleading results with automatic gain control (AGC) aids. A new method using shaped noise has been under study in Working Group S3‐48. This works well with aids having linear, AGC, or adaptive frequency response characteristics, but does not work with aids having speech versus noise discrimination based on detection of the modulation of the received signal. This paper proposes an extension of the shaped noise method that seems to work well with aids having modulation detection. The proposed method uses a combination of pulsed, shaped noise and continuous bandlimited noise as the test signal. The analysis is by two‐channel FFT methods. Examples of appropriate and inappropriate measurement methods will be shown for all types of aids mentioned above.