LPC Filter Quantization Using Multi-Reference Variable Bit Rate Coding
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Solution Overview
Problem
Current speech and audio coding techniques face challenges in efficiently representing LPC filters with a variable bit rate while maintaining subjective quality, particularly in applications requiring low bit rates and mixed content encoding.
Innovation Solution
The proposed solution involves a multi-reference differential quantization method for LPC filters, where the LPC filter is differentially quantized relative to various possible references, including past or future quantized filters, or results of extrapolation/interpolation operations, with a selector choosing the reference that minimizes distortion or bit rate, and a switched absolute/differential quantization scheme to adapt to changing signal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If fixed bit rate quantization is used for LPC filters, then implementation is simple, but bit rate efficiency is poor
Solution Approach 1:
The patent implements variable bit rate quantization where the number of bits allocated to LPC filter quantization varies dynamically based on signal characteristics and coding mode. The system switches between different quantization schemes (full quantization, differential quantization, selective quantization) depending on whether the frame contains speech or music, thereby optimizing bit rate efficiency while adapting to changing signal conditions.
Solution Approach 2:
The patent changes the quantization parameters (number of bits, quantization scheme type) based on the coding mode and signal properties. In music frames, LPC quantization is omitted entirely; in speech frames, variable bit allocation is applied based on the selected speech coding mode, thus adapting the parameter set to minimize overall bit rate while maintaining quality.
2Reliability
If LPC filter is transmitted every frame, then quality is maintained, but bit rate increases
Solution Approach 1:
The patent extracts and transmits LPC filter parameters only when necessary - specifically only in speech-coded frames and only when the selected speech mode requires it. In music frames and in frames coded with other speech modes, LPC transmission is omitted entirely, thus reducing overall bit rate while maintaining quality where it matters.
Solution Approach 2:
Instead of transmitting LPC filters for every frame (excessive action), the patent applies partial quantization/transmission only to the necessary subset of frames (speech frames with appropriate coding modes). This partial action approach reduces bit rate consumption while maintaining sufficient reconstruction quality for speech segments.
3Quantity of substance
If variable bit rate quantization is implemented, then bit rate efficiency improves, but complexity of quantization scheme increases
Solution Approach 1:
The patent segments the quantization process into distinct schemes based on coding mode: full quantization for certain speech modes, differential quantization for other speech modes, and no quantization for music frames. This segmentation allows the system to apply the appropriate level of complexity only when needed, optimizing the trade-off between bit rate efficiency and implementation complexity.
Solution Approach 2:
The patent introduces a mode selection mechanism that acts as an intermediary, deciding which quantization scheme to apply based on the coding mode and signal characteristics. This intermediary layer simplifies the overall system by automatically selecting the appropriate quantization approach, avoiding the need for complex real-time optimization while still achieving variable bit rate efficiency.
Data Source
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AI summary
A device and a method for quantizing a LPC filter in the form of an input vector in a quantization domain, comprises a calculator of a first-stage approximation of the input vector, a subtractor of the first-stage approximation from the input vector to produce a residual vector, a calculator of a weighting function from the first-stage approximation, a warper of the residual vector with the weighting function, and a quantizer of the weighted residual vector to supply a quantized weighted residual vector. A device and a method for inverse quantizing of a LPC filter, comprises means for receiving coded indices representative of a first-stage approximation of a vector representative of the LPC filter in a quantization domain and of a quantized weighted residual version of the vector, a calculator of an inverse weighting function from the first-stage approximation, an inverse quantizer of the quantized weighted residual version of the vector to produce a weighted residual vector, a multiplier of the weighted residual vector by the inverse weighting function to produce a residual vector, and an adder of the first-stage approximation with the residual vector to produce the vector representative of the LPC filter in the quantization domain.