Method and Apparatus for Introducing Information into a Data Stream and Method and Apparatus for Encoding an Audio Signal

Abstract

An inventive method for introducing information into a data stream including data about spectral values representing a short-term spectrum of an audio signal first performs a processing of the data stream to obtain the spectral values of the short-term spectrum of the audio signal. Apart from that, the information to be introduced are combined with a spread sequence to obtain a spread information signal, whereupon a spectral representation of the spread information is generated which will then be weighted with an established psychoacoustic maskable noise energy to generate a weighted information signal, wherein the energy of the introduced information is substantially equal to or below the psychoacoustic masking threshold. The weighted information signal and the spectral values of the short-term spectrum of the audio signal will then be summed and afterwards processed again to obtain a processed data stream including both audio information and information to be introduced. By the fact that the information to be introduced are introduced into the data stream without changing to the time domain, the block rastering underlying the short-term spectrum will not be touched, so that introducing a watermark will not lead to tandem encoding effects.

1 . Apparatus for encoding an audio signal, comprising;
 a generator for generating a short-term spectrum of the audio signal comprising a plurality of spectral values;   a calculator for computing a psychoacoustic masking threshold of the audio signal using a psychoacoustic model;   a quantizer for quantizing spectral values considering the psychoacoustic masking threshold so that noise energy introduced by quantizing is smaller than the psychoacoustic masking threshold by a predetermined amount;   a bitstream formatter for forming a bit stream, the bit stream comprising values corresponding to the quantized spectral values of the short-term spectrum and an indication for the value of the predetermined amount.   
     
     
         2 . Method of encoding an audio signal, comprising;
 generating a short-term spectrum of the audio signal comprising a plurality of spectral values;   computing a psychoacoustic masking threshold of the audio signal using a psychoacoustic model;   quantizing spectral values considering the psychoacoustic masking threshold so that noise energy introduced by quantizing is smaller than the psychoacoustic masking threshold by a predetermined amount;   forming a bit stream, the bit stream comprising values corresponding to the quantized spectral values of the short-term spectrum and an indication for the value of the predetermined amount.