A nine-octave multirate filter with one-third-octave band gain control is presented. The filter, developed as a DSP (digital signal processing) application, produces a random-noise spectrum from 10 Hz to 5 kHz with a controllable level in one-third-octave bands. Nine FIR (finite impulse response) bandpass filters processed at different sample rates and eight FIR low-pass interpolation filters provide shaped pseudorandom noise. Equipment includes the TI TMS320C25-based software development system and the TLC32041 analog interface chip. The design offers a significant saving in both data memory storage and processing time. The multirate filter program uses 1368 words of data memory, whereas an equivalent single rate would occupy 41 K words of data memory.
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