Audio encoder and decoder
First Claim
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1. Audio coding system comprising:
- a linear prediction (LP) unit for filtering an audio signal based on a LP filter, the LP unit operating on a first frame length of the audio signal;
an adaptive length transformation unit for transforming a frame of the audio signal into a transform domain, the transformation being a Modified Discrete Cosine Transform (MDCT) operating on a variable second frame length;
a quantization unit for quantizing a MDCT-domain signal;
a gain curve generation unit for generating MDCT-domain gain curves based on magnitude responses of the LP filter; and
a mapping unit for mapping LP parameters to corresponding frames of the MDCT-domain signal;
wherein the mapping unit interpolates LP polynomials generated on a rate corresponding to the first frame length so as to match frames of the MDCT-domain signal generated on a rate corresponding to the second frame length for usage as perceptual weights in the quantization unit.
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Abstract
The present invention teaches a new audio coding system that can code both general audio and speech signals well at low bit rates. A proposed audio coding system comprises linear prediction unit for filtering an input signal based on an adaptive filter; a transformation unit for transforming a frame of the filtered input signal into a transform domain; and a quantization unit for quantizing the transform domain signal. The quantization unit decides, based on input signal characteristics, to encode the transform domain signal with a model-based quantizer or a non-model-based quantizer. Preferably, the decision is based on the frame size applied by the transformation unit.
44 Citations
14 Claims
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1. Audio coding system comprising:
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a linear prediction (LP) unit for filtering an audio signal based on a LP filter, the LP unit operating on a first frame length of the audio signal; an adaptive length transformation unit for transforming a frame of the audio signal into a transform domain, the transformation being a Modified Discrete Cosine Transform (MDCT) operating on a variable second frame length; a quantization unit for quantizing a MDCT-domain signal; a gain curve generation unit for generating MDCT-domain gain curves based on magnitude responses of the LP filter; and a mapping unit for mapping LP parameters to corresponding frames of the MDCT-domain signal;
wherein the mapping unit interpolates LP polynomials generated on a rate corresponding to the first frame length so as to match frames of the MDCT-domain signal generated on a rate corresponding to the second frame length for usage as perceptual weights in the quantization unit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. Audio decoder comprising:
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a de-quantization unit for reconstructing quantized MDCT lines received in an input bitstream; an adaptive length Inverse MDCT transformation unit for inversely transforming a transform domain signal into a time domain signal, the inverse MDCT transformation unit operating on a variable frame length; a gain curve generation unit for generating MDCT-domain gain curves based on magnitude responses of linear prediction filters, wherein parameters for the linear prediction filters are received in the bitstream and correspond to a first frame length; and
a mapping unit for mapping LP parameters to corresponding frames of the MDCT-domain signal;
wherein the mapping unit interpolates LP polynomials generated on a rate corresponding to the first frame length so as to match frames of the transform domain signal generated on a rate corresponding to the second frame length for usage as perceptual weights in the de-quantization unit.
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13. Audio encoding method comprising the steps:
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performing a linear prediction (LP) analysis on an audio signal, the LP analysis operating on a first frame length and generating LP parameters; transforming a frame of the audio signal into a Modified Discrete Cosine Transform (MDCT)-domain, the MDCT operating on a variable second frame length; quantizing a MDCT-domain signal; generating MDCT-domain gain curves based on magnitude responses of the generated LP filters; and mapping LP parameters to corresponding frames of the MDCT-domain signal; wherein mapping comprises interpolating LP polynomials generated on a rate corresponding to the first frame length so as to match frames of the MDCT-domain signal generated on a rate corresponding to the second frame length for usage as perceptual weights for quantizing the MDCT-domain signal.
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14. Audio decoding method comprising the steps:
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reconstructing quantized MDCT lines received in an input bitstream; inverse Modified Discrete Cosine-transforming (MDCT) a transform domain signal into a time domain signal, the inverse MDCT operating on a variable frame length; generating MDCT-domain gain curves based on magnitude responses of linear prediction filters, wherein parameters for the linear prediction filters are received in the bitstream and correspond to a first frame length; and mapping LP parameters to corresponding frames of the MDCT-domain signal; wherein mapping comprises interpolating LP polynomials generated on a rate corresponding to the first frame length so as to match frames of the MDCT-domain signal generated on a rate corresponding to the second frame length for usage as perceptual weights for quantizing the MDCT-domain signal.
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Specification