An audio limiting circuit capable of satisfying frequency dependent limits and
time domain constraints, is disclosed. In one illustrative embodiment, an input
node receives an unattenuated input signal and a system modeling filter predicts
the amount, if any, by which the sound pressure level that would be generated by
an acoustic transducer in response to the unattenuated input signal, would exceed
one or more predetermined limits. In that embodiment, an energy detector separates
the excess predicted sound pressure level into one or more frequency bands and
calculates the average acoustic energy associated with each band. A gain logic
block determines an attenuation factor based on whether one or more of the predetermined
limits has been exceeded and the attenuation factor values are smoothed to minimize
abrupt changes to the unattenuated input signal. A delay buffer delays the unattenuated
input signal values. Finally, in the embodiment described here, the smoothed attenuation
factor values are synchronized with and applied to the delayed input signal values
and the resulting attenuated signal is transmitted to an output node and ultimately
to one or more acoustic transducers.