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Abstract

A method of (and apparatus for) extending the useful dynamic range of an audio reproduction system. An input acoustic signal in the audible range is transduced to form an analog electric signal which is amplified along parallel paths to gain levels g.sub.1 and g.sub.2 (where g.sub.2 >g.sub.1), the amplified signals being sampled to provide two binary digital signals. The analog signal consists of a high amplitude portion and a low amplitude portion. The two binary digital signals are processed by a computer which provides a first binary output and a second binary output, the first binary output being a digital representation of the sequential samples of the audio signal taken at the respective gain setting g.sub.1 or g.sub.2. More precisely, the first binary digital output is a composite binary digital waveform consisting of a high amplitude portion at gain setting g.sub.1, a low amplitude portion at gain setting g.sub.2 and a transition or cross-fade portion therebetween. The second binary output is a digital representation of the output gain required to normalize the effect of the particular input gain setting g.sub.1 or g.sub.2 on the final output such that the product of input gain and output gain remains constant. The second binary output signal is fed to an interpolator, then converted to analog and connected as an analog signal to a multiplying D/A which receives, also, the first binary digital output. The multiplying D/A provides an output analog signal derived initially from the high amplitude input portion which was amplified to gain g.sub.1, followed by the low amplitude input portion which was amplified to gain g.sub.2, the transition or cross-fade portion therebetween being a blend of the two and the gain thereof being modified as it is blended.

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