Efficient spectral envelope coding using variable time/frequency resolution and time/frequency switching
AssigneeCoding Technologies AB
InventorsLars Gustaf Liljeryd, Kristofer Kjorling, Per Ekstrand, Fredrik Henn
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Abstract
The present invention provides a new method and an apparatus for spectral envelope encoding. The invention teaches how to perform and signal compactly a time/frequency mapping of the envelope representation, and further, encode the spectral envelope data efficiently using adaptive time/frequency directional coding. The method is applicable to both natural audio coding and speech coding systems and is especially suited for coders using SBR [WO 98/57436] or other high frequency reconstruction methods.
Claims19
A method for spectral envelope encoding for an input signal, the input signal having a bandwidth, the bandwidth including certain frequency regions, the input signal being represented by a source encoded version thereof, the source encoded version having a bandwidth not including the certain frequency regions, a spectral envelope of the input signal in the certain frequency regions being representable by a coarse spectral envelope representation and a fine spectral envelope representation, the fine spectral envelope representation being a residual signal, comprising the following steps:
- performing a statistical analysis of the input signal;
- based on an outcome of the statistical analysis, generating data on the coarse spectral envelope representation for the certain frequency regions by sampling the spectral envelope in the certain frequency regions with a varying time resolution or a varying frequency resolution, wherein a time resolution or a frequency resolution selected for a time instant depends on the outcome of the statistical analysis of the input signal at the time instant;
- generating a control signal describing the varying time resolution or the varying frequency resolution;
- and
- generating an encoded input signal by multiplexing the source encoded version, the data on the coarse spectral envelope representation and the control signal, wherein the encoded input signal does not include the residual signal.
An apparatus for spectral envelope encoding for an input signal the input signal having a bandwidth, the bandwidth including certain frequency regions, the input signal being represented by a source encoded version thereof, the source encoded version having a bandwidth not including the certain frequency regions, a spectral envelope of the input signal in the certain frequency regions being representable by a coarse spectral envelope representation and a fine spectral envelope representation, the fine spectral envelope representation being a residual signal, comprising:
- means for performing a statistical analysis of the input signal,
- means for generating data, based on the outcome of the statistical analysis, on the coarse spectral envelope representation for the certain frequency regions by sampling the spectral envelope in the certain frequency regions with a varying time resolution or a varying frequency resolution, wherein a time resolution or a frequency resolution selected for a time instant depends on the outcome of the statistical analysis of the input signal at the time instant,
- generating a control signal describing the varying time resolution or the varying frequency resolution;
- and
- generating an encoded input signal by multiplexing the source encoded version, the data on the coarse spectral envelope representation and the control signal, wherein the encoded input signal does not include the residual signal.
An apparatus for spectral envelope decoding an encoded signal, the encoded signal including a source encoded version of an original signal, the original signal having a bandwidth including certain frequency regions, the source encoded version having a bandwidth not including the certain frequency regions, data on a coarse spectral envelope representation representing the spectral envelope with a varying time resolution or a varying frequency resolution, and a control signal indicating the varying time resolution or the varying frequency resolution, the source encoded signal resulting, after source decoding, in a decoded version of the original signal, the decoded version of the original signal having a bandwidth not including the certain frequency regions;
- a demultiplexer for demultiplexing the encoded signal to obtain the source encoded version, the data on the coarse spectral envelope representation and the control signal;
- means for generating a spectral band replicated signal for the certain frequency regions;
- means for interpreting the control signal in order to determine the varying time resolution or the varying frequency resolution,
- means for envelope adjusting the spectral band replicated signal using the data on the coarse spectral envelope information and the varying time resolution or the varying frequency resolution;
- and
- means for adding the envelope adjusted signal and the decoded version of the original signal to obtain a decoded signal having a bandwidth including the certain frequency regions.
A method of spectral envelope decoding an encoded signal, the encoded signal including a source encoded version of an original signal, the original signal having a bandwidth including certain frequency regions, the source encoded version having a bandwidth not including the certain frequency regions, data on a coarse spectral envelope representation for the certain frequency regions, the data on the coarse spectral envelope representation representing the spectral envelope with a varying time resolution or a varying frequency resolution, and a control signal indicating the varying time resolution or the varying frequency resolution, the source encoded signal resulting, after source decoding, in a decoded version of the original signal, the decoded version of the original signal having a bandwidth not including the certain frequency regions, comprising the following steps:
- demultiplexing the encoded signal to obtain the source encoded version, the data on the coarse spectral envelope representation and the control signal;
- generating a spectral band replicated signal for the certain frequency regions;
- interpreting the control signal in order to determine the varying time resolution or the varying frequency resolution,
- envelope adjusting the spectral band replicated signal using the data on the coarse spectral envelope information and the varying time resolution and the varying frequency resolution;
- and
- adding the envelope adjusted signal and the decoded version of the original signal to obtain a decoded signal having a bandwidth including the certain frequency regions.
Dependencies are inferred from the claim text.