| 摘要 |
This invention discloses a method and a plurality of compressive amplitude distortion units for enhancing the perceptibility of the low-frequency portion of a sound by introducing residue harmonics of low-frequency signal components into the sound, where the residue harmonics are generated by a nonlinear function emulating the middle-ear response of a human being. The low-frequency portion in the resultant sound is perceivable to a human listener even if this portion is removed from this sound. In one embodiment, a compressive amplitude distortion unit comprises: a low pass filter for extracting low-frequency components of the input sound signal; a compressive amplitude function processor for generating a harmonics-containing signal from the low-pass signal by a nonlinear function emulating the middle-ear response; a gain block for scaling the harmonics-containing signal such that the signal strength of the scaled harmonics-containing signal is in the same range as that of the initial low-pass signal; an adder for adding the input sound signal and the scaled harmonics-containing signal; and a high pass filter for removing the low-frequency signal components in the output sound signal while still including the residue harmonics. Based on the disclosed method, this invention also discloses two anti-piracy methods that utilize the absence of low-frequency signal components in a sound signal, one for convenient detection of an unauthorized copy of the processed sound signal, another one for discouraging people to make such an unauthorized copy.
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