Hearing impairment is the number one chronic disability affecting people in the world. Many people have great difficulty in understanding speech with background noise. This is especially true for a large number of elderly people and the sensorineural impaired persons. Several investigations on speech intelligibility have demonstrated that subjects with sensorineural loss may need a 5-15 dB higher signal-to-noise ratio than the normal hearing subjects. While most defects in transmission chain up to cochlea can nowadays be successfully rehabilitated by means of surgery, the great majority of the remaining inoperable cases are sensorineural hearing impaired. Recent statistics of the hearing impaired patients applying for a hearing aid reveal that 20% of the cases are due to conductive losses, more than 50% are due to sensorineud losses, and the rest 30% of the cases are of mixed origin.
[...] In both the cases, it is-difficult to obtain and evaluate various frequency response characteristics Digital hearing aids In digital hearing aid, a microprocessor or ASIC replaces the hardware used to process the signal (e.g., filtering, compression). The analog output of the microphone will be low-pass-filtered to prevent aliasing errors, sampled at discrete intervals, and will be converted to binary form using an analog-to-digital converter. The digital signal will be processed in the manner in which the microprocessor has been programmed. [...]
[...] are shown in Fig The outer ear and ear canal collect sound, which is directed to the eardrum. The ear canal acts as a quarter wavelength resonator, which increases the acoustic signal level over a frequency range from 1 kHz to 3 kHz. The middle ear includes the eardrum and three small bones (ossicles) that conduct sound from the canal to the inner ear. The middle ear structures vibrate in complex modes and serve as an impedance transformer between airborne sound in the ear canal and fluid-borne sound in the inner ear. [...]
[...] In summery, we had developed and verified signal processing algorithm to enhance speech singals far the hearing impaired. -20 Magnitude in dB -40 -60 -80 - Hz Figure 6 : Multiplication with numerical value by 3942 Difference in db of frequency plot of two speech files 80 References : Arlene C. Neuman : Digital technology md clinical practice : The outlook for the future , Journal of Rehabilitation Research and development, (1987) R.C.Bilger and I. J.Hirsch : Hearing Aid Evaluation: [...]
[...] Programmability Much greater precision in adjusting electro acoustic parameters Self monitoring capabilities Logical operations for self-testing and selfcalibration The use of advanced signal processing technique for noise reduction Automatic control of signal levels. Only a few of these features are likely to be included in the first generation wearable digital hearing aids because of the constraints on chip size and power consumption. Although the concept of a digital hearing aid was anticipated at an early date, two major technical problems had to be resolved before anyone could develop a wearable digital hearing aid. [...]
[...] The second and more difficult problem is that of developing digital circuitry that is small enough and sufficiently low in power consumption for practical use in a small wearable unit Speech Enhancement using Wavelet Like the fast Fourier transform, the discrete wavelet transform is a fast, linear operation that operates on a data vector whose length is an integer power of two, transforming it into a numerically different vector of the same length. In the wavlet domain, the basis functions are somewhat more complicated and have the fanciful name “mother function” and “wavlets”. [...]
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