QUALITY IMPROVEMENT TECHNIQUES IN AN AUDIO ENCODER
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Abstract
An audio encoder implements multi-channel coding decision, band truncation, multi-channel rematrixing, and header reduction techniques to improve quality and coding efficiency. In the multi-channel coding decision technique, the audio encoder dynamically selects between joint and independent coding of a multi-channel audio signal via an open-loop decision based upon (a) energy separation between the coding channels, and (b) the disparity between excitation patterns of the separate input channels. In the band truncation technique, the audio encoder performs open-loop band truncation at a cut-off frequency based on a target perceptual quality measure. In multi-channel rematrixing technique, the audio encoder suppresses certain coefficients of a difference channel by scaling according to a scale factor, which is based on current average levels of perceptual quality, current rate control buffer fullness, coding mode, and the amount of channel separation in the source. In the header reduction technique, the audio encoder selectively modifies the quantization step size of zeroed quantization bands so as to encode in fewer frame header bits.
112 Citations
36 Claims
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1-15. -15. (canceled)
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16. In a transform-based audio encoder, a method of improved band truncation, the method comprising:
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performing a transform on a portion of an input audio signal to produce a set of transform domain coefficients;
selecting as an open-loop process a portion of the transform domain coefficients for band truncation as a function of a target quality measurement;
suppressing the selected portion of the transform domain coefficients from encoding in a compressed audio data stream. - View Dependent Claims (17, 18, 19)
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20. (canceled)
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21. In a transform-based audio encoder, a method of encoding a multi-channel audio input signal, the method comprising:
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performing a multi-channel transformation on multiple input channels of the multi-channel audio input signal to produce a plurality of joint coding channels;
selectively suppressing at least one of the joint coding channels as a function of at least quality of reproduction, rate control buffer fullness, and channel separation; and
encoding the multi-channel audio input signal with said selective suppression of said at least one joint coding channel. - View Dependent Claims (22, 23, 24, 25)
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26. (canceled)
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27. (canceled)
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28. In a transform-based audio encoder, a method of improving coding efficiency, the method comprising:
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converting a block of samples of an input signal into a plurality of transform domain coefficients;
quantizing the transform domain coefficients according to quantization step-size values of quantization bands for the transform domain coefficients;
identifying any quantization bands of transform domain coefficients that are quantized to zero;
modifying the quantization step-size value of said any identified quantization bands to encode in fewer bits in a quantization matrix; and
encoding the quantization step-size values of the quantization bands in the quantization matrix. - View Dependent Claims (29, 30, 31, 32, 33, 34)
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35. (canceled)
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36. (canceled)
Specification