Method of transmitting or storing masked sub-band coded audio signals
DCFirst Claim
1. In a method of transmitting or storing digitalized audio signals having spectral and temporal structure, wherein each audio signal is represented by a plurality of spectral, quantized components, the method comprising the steps of:
- producing the plurality of spectral, quantized components from the digitalized audio signal, with each component having respective level values associated with the spectral and temporal structure of the audio signal;
obtaining masking thresholds corresponding to the human auditory system for each component;
changing the quantizing of the individual components on the basis of the respective masking thresholds of the human auditory system to produce coded components, thereby reducing the magnitude of a total information flow required for the transmission or storage of all coded components which fluctuates in dependence on the spectral and temporal structure of the audio signal;
transmitting or storing the coded components;
decoding the transmitted or stored coded components; and
reconstructing a broadband, digital audio signal from the decoded components;
the improvement wherein the step of changing the quantizing of the components is on the basis of the level values of each component so that the quantizing noise levels of the individual components have approximately the same level difference from the respective masking threshold of the individual components, the differences of the quantizing noise levels of the components being set by the difference between the required total information flow and the total information flow available for coding.
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Abstract
In the transmission of audio signals, the audio signal is digitally represented by use of quadrature mirror filtering in the form a plurality of spectral sub-band signals. The quantizing of the sample values in the sub-bands, e.g. 24 sub-bands, is controlled to the extent that the quantizing noise levels of the individual sub-band signals are at approximately the same level difference from the masking threshold of the human auditory system resulting from the individual sub-band signals. The differences of the quantizing noise levels of the sub-band signals with respect to the resulting masking threshold are set by the difference between the total information flow required for coding and the total information flow available for coding. The available total information flow is set and may then fluctuate as a function of the signal.
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Citations
29 Claims
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1. In a method of transmitting or storing digitalized audio signals having spectral and temporal structure, wherein each audio signal is represented by a plurality of spectral, quantized components, the method comprising the steps of:
- producing the plurality of spectral, quantized components from the digitalized audio signal, with each component having respective level values associated with the spectral and temporal structure of the audio signal;
obtaining masking thresholds corresponding to the human auditory system for each component;
changing the quantizing of the individual components on the basis of the respective masking thresholds of the human auditory system to produce coded components, thereby reducing the magnitude of a total information flow required for the transmission or storage of all coded components which fluctuates in dependence on the spectral and temporal structure of the audio signal;
transmitting or storing the coded components;
decoding the transmitted or stored coded components; and
reconstructing a broadband, digital audio signal from the decoded components;the improvement wherein the step of changing the quantizing of the components is on the basis of the level values of each component so that the quantizing noise levels of the individual components have approximately the same level difference from the respective masking threshold of the individual components, the differences of the quantizing noise levels of the components being set by the difference between the required total information flow and the total information flow available for coding.
- producing the plurality of spectral, quantized components from the digitalized audio signal, with each component having respective level values associated with the spectral and temporal structure of the audio signal;
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2. In a method of transmitting or storing digitalized audio signals represented by a plurality of spectral, quantized components, the method comprising the steps of:
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(a) determining level values of each said quantized component of said digitalized audio signal; (b) obtaining masking thresholds based on the human auditory system and the determined level values of said individual components; (c) changing the quantizing of said components on the basis of said masking thresholds of the human auditory system to produce coded components; (d) transmitting or storing said coded components; (e) decoding the transmitted or stored coded components; and (f) reconstructing a broadband, digital audio signal from the decoded components; the improvement wherein said step of changing the quantizing of said components is made such that quantizing noise levels of the individual components produced during the quantizing of an audio signal to provide the digitalized audio signal have approximately an equal level difference from the respective masking thresholds of the individual components, and said approximately equal level differences are set by the difference between (i) a total information flow required for the transmission or storage of said coded components, and (ii) a total information flow available for coding. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23, 24, 25, 26, 27, 28, 29)
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22. Method according to claim to 20, wherein the scale factor of a sub-band contains information indicating that the sample values of the sub-band are zero within one block and are not transmitted.
Specification