There is provided an evaluation system for an A-D converter or a D-A converter capable of evaluating factors of a compounded fault and measuring an effective number of bits with a high accuracy and with a reduced volume of computation, independently of a testing frequency. A sine wave signal is applied to an A-D converter under test. Maximal or minimal values of a cosine wave component and a sine wave component in the converted output are aligned. A square root of a sum of squares of samples is formed to determine an instantaneous amplitude. The amplitude of the sine wave signal is interleaved into the series of instantaneous amplitudes. A difference series for the interleaved instantaneous amplitude series is formed by digital moving differentiator means. Alternatively, a Wavelet transform is applied to the interleaved instantaneous amplitude series, and a maximum amplitude therein is detected by a peak finder, and the detected value is delivered as representing an estimated effective number of bits.
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