Making use of a digital acoustic signal processing apparatus arranged by employing memory device for storing a digital acoustic signal, acoustic frequency feature enhancing device for enhancing an acoustic frequency feature, and low-speed sound reproducing device for changing a speed of the stored voice to reproduce this voice as a low speed into a hearing aid and an appliance with an acoustic output, a hearing function difficulty due to an age is aided in utilization of audio output appliances such as a hearing aid, television receiver, and a telephone receiver. After the voice has been stored in the memory device, a process for enhancing the frequency characteristic in order to fit the frequency characteristic to the individual hearing characteristic and the voice reproducing environment is carried out and thereafter represented to the user. The user can repeatedly listen the voice stored in the memory device with employment of control device for controlling the voice reproducing operation. Furthermore, since a process for expanding a time scale during a sound reproducing operation is carried out, the voice can be represented at the low speed. Since the voice whose frequency characteristic has been enhanced can be represented at the low speed in order that either an individual hearing ability, or an apparatus is fitted to a using environment, hearing articulation can be improved with respect to such a hearing, the frequency resolution and the time resolution are simultaneously deteriorated.