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In this paper a hearing aid concept working in subbands is presented. Consideration is given to the compensator for recruitment of loudness and the acoustic feedback cancellation. In addition, a step-size control for fast tracking and a constant error level with non-stationary input s8ignals is presented. The feedback canceler is adapted to the feedback path in the transform domain using a power-normalized least mean square (LMS) algorithm. The transformation into subbands is based on the modulated lapped transform (MLT). Together with the feedback canceler the proposed hearing-loss compensating forward filter is computationally very efficient. INTRODUCTIONHearing-impaired persons with loudness recruitment have a reduced range between the sound-pressure levels (SPL) corresponding to threshold (THR) and discomfort (UCL).to map real world signals into this compressed comfort range, a frequency-and magnitude-dependent compensator has to be provided. An echo canceler is further needed to provide large gains in the compensator [6]. It can prevent the overall system from howling and becoming unstable. PROPOSED SYSTEMTransform-domain schemes allow a computationally efficient implementation of a digital hearing aid [7, 10, 131. The proposed system (Fig. 2) works with the augmented MLT (AMLT) [I 21. We used a predictor with 32 uniform bands which reduces the feedback enough to add an additional gain of more than 10dB to the compensator compared to a system without predictor. To prevent to ear drum input (e.g. speech) 20Hz 50H7 IUOH, ZWHz 5WHz lkHz Zktt! 5Wz 1OWz ZOkHr frequency Figure 1: Hearing area with threshold of hearing (THR) and upper comfort limit (UCL) for normal hearing people (index N) and people with sensorineural hearing impairment (index I ) .In Fig. 1 the audible frequency range from 20Hz to 16kHz is subdivided into 24 abutting critical bands (denoted 1 . . .24) [ 141.The critical bands are closely related to several characteristics of the hearing system although the auditory filters become wider for hearing impaired people [ l , 21. As a result of loudness recruitment, the effective dynamic range of a hearing-impaired person is compressed. It often varies markedly with frequency.

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