Method of distortion-free signal compression

摘要

An audio signal in which an audio signal is received as a stream of digital samples, each being a numerical value representing a sampled signal level. A first zero crossing point is identified and the received audio samples are stored until a second zero crossing point is identified, thereby storing a first half-wave of samples. The highest intensity sample is identified from the stored samples and this is compared against a predetermined threshold. All stored samples are scaled by an initial scaling factor so that the intensity of the highest intensity sample is not above this threshold. A second half-wave of samples is stored in which all samples of the second half-wave are below the threshold. All stored samples of the second half-wave are also scaled but by a modified scaling factor derived from a combination of the initial scaling factor and a decay factor.

主权项

1. A compression apparatus for compressing the level of an audio signal, comprising an input device, an identification device, a storage device, and a scaling device, wherein:
said input device is configured to receive an audio signal as a stream of digital samples, each sample being a numerical value representing a sampled signal level; said identification device is configured to identify a first zero crossing point; said storage device is configured to store the received audio samples until a second zero crossing point is identified by said identification device, thereby storing a first half-wave of samples; said identification device is configured to identify the highest intensity sample of said stored samples, and to compare said highest intensity sample against a threshold intensity; said scaling device is configured to scale all stored samples of said first half-wave by an initial scaling factor that is less than unity so that the intensity of said highest intensity sample is not above said threshold intensity; said storage device is configured to store a second half-wave of samples in which all samples of the second half-wave are below said threshold intensity; and said scaling device is configured to scale all stored samples of said second half-wave by a first modified scaling factor having a value between that of the initial scaling factor and unity, and which is derived by combining the initial scaling factor with a decay factor.