IHCON_poster02 - Novel Numerical Representations for...

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Most of the computations the hearing aid is performing are multiply-accumulates. Novel Numerical Representations for Low-Power Audio Signal Processing Roger Chamberlain*†, Yen Hsiang Chew*, Varuna DeAlwis*, Eric Hemmeter*, John Lockwood*, Robert Morley*, Ed Richter*, Jason White*, and Huakai Zhang* *School of Engineering and Applied Science, Washington University, St. Louis, MO †Hearing Emulations, LLC and BECS Technology, Inc., St. Louis, MO Power Is Used Charging Capacitance Hearing Aid Architecture Multiplication vs. Addition We can see from these examples that many more bits are needed to perform a multiplication than to perform an addition. 10101 x 11001 10101 00000_ 00000__ 10101___ _10101____ 1000001101 10101 + 11001 101110 Using a logarithmic representation of the audio signals allows us to take advantage of this difference in the effort to reduce power needed. By using a logarithmic representation we can replace the multipliers with adders, because log(A x B) = log(A) + log(B) However, then the adder must be modified as well. Lets start with this: log1 + B A = log A + B A = log A + B log A We want log(A+B), so: Since this would be harder to calculate than the original multiplication and addition, this function is performed by a look-up table. To eliminate even more unnecessary calculations, the look-up table is only accessed if the two inputs to the “adder”, i.e., the log multiplier, are significant with respect to each other. In other words, if one of the values is small enough to be negligible then the look- up is skipped and the larger number passed through, thus saving more power. log A + B = log A + log1 + B A Abstract One of the major technical issues facing the designers of modern digital hearing aids is the need to minimize the power consumption of the system to prolong battery life. As new signal processing techniques are proposed, the computational requirements invariably grow, putting additional pressure on power consumption. In this work, we investigate the use of non-standard numerical representations for the audio signals being processed, showing how the power consumption can be lowered for audio signal processing while maintaining (and even improving) overall signal quality.
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This document was uploaded on 11/13/2009.

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IHCON_poster02 - Novel Numerical Representations for...

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