Excessive program levels can cause strange distortions during digitization. While the clipping of an analog audio signal produces a well-known harmonic distortion, the overload of the ADC results in the appearance of non-harmonic components. The human sense of aliasing effect is usually more dubious than the sense of harmonic distortion, so spurious sounds are more likely to get into a digital recording because of an overload, than in an anlog one. It is especially dangerous, when pre-emphasis is applied prior to the A/D conversion. Theoretical and experimental investigations of these phenomena show that this problem can be reduced significantly by means of a very simple circuit.
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