A dynamic range compression system is provided, using either a
sample-by-sample or a block processing system. Such a system can be used,
for example, in a hearing aid. The system, using a frequency-warped
processing system, is comprised of a cascade of all-pass filters with the
outputs of the all-pass filters providing the input to the frequency
analysis used to compute the filter coefficients. The compression filter
is then designed in the frequency domain. Using a compression filter
having even symmetry guarantees that the group delay is constant and does
not depend on the compression gains at any given time. Additionally, due
to the use of all-pass filters, the compression filter group delay more
closely matches human auditory latency. An inverse frequency transform
back into the warped time domain is used to produce the compression
filter coefficients that are convolved with the outputs of the all-pass
delay line to give the processed output signal.