A digital filter is an essential structure in present day electronic devices. There is a variety of applications which demands tunability of digital filters in terms of bandwidth. It is desirable to have simple design process and minimum possible overhead in hardware implementation. A set of very low order subfilters derived from Farrow structure is proposed to function as a sample rate converter on the input signal. A fixed bandwidth low pass filter is placed in between these interpolator structures, resulting in a continuously variable bandwidth filter (CVF). This hardware efficient CVF architecture helps to achieve the tunability without altering the coefficients and the underlying structure. This model obtains a continuous variation in bandwidth employing a single sample rate change factor. Very low complexity and easy tunability of this technique are highly motivating factors to adopt CVF in various real-world applications.
Design of a digital hearing aid requires a set of filters that gives reasonable audiogram matching for the concerned type of hearing loss. This paper proposes the use of a variable bandwidth filter, using Farrow subfilters, for this purpose. The design of the variable bandwidth filter is carried out for a set of selected bandwidths. Each of these bands is frequency shifted and provided with sufficient magnitude gain, such that, the different bands combine to give a frequency response that closely matches the audiogram. Due to the adjustable bandedges in the basic filter, this technique allows the designer to add reconfigurability to the system. This technique is simple and efficient when compared with the existing methods. Results show that lower order filters and better audiogram matching with lesser matching errors are obtained using Farrow structure. This, in turn reduces implementation complexity. The cost effectiveness of this technique also comes from the fact that, the user can reprogram the same device, once his hearing loss pattern is found to have changed in due course of time, without the need to replace it completely.
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