Noise Shaping in Digital Test-Signal Generation
We extend an idea, proposed in an earlier paper, to use noise-shaping techniques in the generation of digital test signals. The previous paper proposed using noise shaping around an undithered quantizer to generate sinusoidal digital test signals with spectra having error nulls at the harmonics of the signal frequency, thus making digital distortion measurements of very great dynamic range possible. We extend this idea in a number of ways. We show: (a) that dither is necessary in order to suppress spurious artifacts caused by the nonlinearity of an undithered noise shaper, (b) that wider and deeper nulls at the harmonic frequencies can be achieved by using higher-order noise-shaper designs, (c) that IIR filter designs can moderate the increased noise power that accompanies an increased FIR filter order, and (d) some other novel uses of noise shaping in digital signal generation.
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