The paper is about the design of a novel speech processor and its successful incorporation in a vibrotactile speech training aid for the deaf. The introduction makes clear the particular difficulties and needs of the deaf child who is learning to speak. The discussion shows that to help with the deaf child's difficulty with mimicry the technologist must enable the child to sense and compare patterns of articulator configurations. It is suggested that the vocal gestures will be monitored most easily if the speech processor operates in such a way as to ignore variations in speech intensity. An explanation is given of a novel amplitude insensitive filtering system which employs a bank of high-pass filters. A particular requirement of the system is for the measurement of the ratio of two voltages each of which can vary over a wide dynamic range; a circuit for this is presented. Although the discussion focuses on the application of the frequency-analysis system to speech processing the theoretical treatment facilitates the evaluation of the system's potential for processing other signals.