GB1340105A - Aids for deaf persons - Google Patents

Abstract

1340105 Hearing aids NATIONAL RESEARCH DEVELOPMENT CORP 6 June 1972 [8 June 1971] 19476/71 Headings H4J and H4R In an aid for deaf persons (i.e. a hearing aid or a speech training aid) sounds in a first speech frequency range are converted into sounds in a second speech frequency range, the frequency differences of the first range being substantially maintained in the second range, and the converted sounds are superimposed on sounds in the second range. For example, speech components in the range 4000 c.p.s. to 5000 c.p.s. may be changed to have frequency components from 0 to 1000 c.p.s. and be superimposed upon speech components below 1000 c.p.s. An electrical input signal fs (Fig. 2) from a microphone (not shown) is applied to two signal paths 2 and 3. Path 2 includes a frequency modulator 4 of frequency fc, which gives sum and difference output signals fc+fs and fc-fs. A single side band filter 5 passes only a selected range of the modulated signals. Output signal fs<SP>1</SP> from filter 5 is passed to a demodulator 6 where the output signal is demodulated by a signal fc<SP>1</SP> to give an output signal fs<SP>1</SP>-# (where #=fc<SP>1</SP>-fc). Path 3 includes a pre-amplifier 7 and amplifier 8 for signal fs. The signal fs<SP>1</SP> - # passes to amplifier 8 by way of a resistor 9 and is superimposed upon the pre-amplified input signal fs within amplifier 8. The amplified signal fs+(fs<SP>1</SP> - #) from amplifier 8 passes by way of a filter arrangement 10 and an amplitude compressor 11 to a loud-speaker or earphone (not shown). The filter arrangement 10 may comprise a plurality of filters 10a, 10b, 10c controlled by a switch 10d, for selection according to the requirements of a deaf person. Alternatively, a single filter may be provided, tailored to the requirements of the user. A conventional group hearing aid or group speech training aid may have a module comprising the circuit of Fig. 2 connected to its auxiliary input connector. In a speech training aid both direct and recorded speech may be reproduced. Visual and/or tactile aids may also be provided and may be controlled by the changed electrical signal or such changed electrical signal superimposed upon the unchanged electrical signal.