Perceptual Audio Encoder Rate Control via Gradient Gain Adjustment
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Solution Overview
Problem
Digital audio transmission requires efficient compression techniques to eliminate irrelevant and redundant parts of the audio stream, necessitating effective estimation of rate controlling parameters in perceptual audio encoders, especially for low-power devices.
Innovation Solution
The method involves incrementally adjusting a global gain based on the number of bits used to represent a quantized value, limiting the number of loops in the rate controlling parameter, and deriving a global gain to ensure exit from the loop, using gradient-based adjustments and a bail out method to reduce computational complexity and guarantee bit rate compliance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional bit allocation methods are used in perceptual audio encoders, then audio quality can be maintained, but computational complexity increases and processing speed decreases
Solution Approach 1:
The patent pre-calculates and stores bit consumption values for different quantization steps in lookup tables before encoding. During actual encoding, the encoder directly queries these pre-computed tables to determine bit allocation, eliminating the need for complex real-time calculations and significantly reducing computational complexity while maintaining accurate bit rate control
Solution Approach 2:
The patent creates simplified models and approximations of the complex bit allocation problem. By using lookup tables that store pre-computed bit consumption data and applying simplified gradient calculations, the system replicates the functionality of complex optimization algorithms with much lower computational requirements, achieving near-optimal bit allocation efficiency
2Measurement precision
If iterative optimization is applied to estimate rate controlling parameters, then bit rate accuracy improves, but processing time increases
Solution Approach 1:
The patent implements a loop structure that periodically updates the global gain parameter based on bit consumption feedback. The encoder performs iterative adjustments in discrete steps, checking bit usage at each iteration and adjusting the global gain accordingly until the target bit rate is achieved or maximum iterations are reached, balancing accuracy with processing time
Solution Approach 2:
The patent employs feedback mechanisms where the actual bit consumption is measured during encoding and used to adjust the global gain parameter in subsequent iterations. This closed-loop control ensures accurate bit rate compliance while the iterative process converges efficiently by using the measured bit consumption to guide parameter adjustments
3Reliability
If the number of iterations in rate control loop is increased, then bit rate compliance improves, but computational load increases
Solution Approach 1:
The patent applies a maximum iteration limit to the rate control loop, performing partial optimization when the target bit rate is close but not exactly achieved. The system accepts near-optimal solutions after a predetermined number of iterations, avoiding the excessive computational cost of continuing iterations that would yield diminishing returns, thus balancing bit rate compliance with computational efficiency
Data Source
AI summary
Perceptual audio coder refers to audio compression schemes that exploit the properties of human auditory perception. The coder allocates the quantization noise below the masking threshold such that even with the bit rate limitation, the noise is imperceptible to the ear. These distortion and bit rate requirement makes the bit allocation-quantization process a considerable computational effort. One method includes incrementally adjusting a global gain according to a gradient. The gradient could be adjusted each time the number of bits used to represent a quantized value is counted. Another method includes limiting a rate controlling parameter to a predetermined number of loops. The method could also include deriving a global gain to ensure exit from the loop. Accordingly, embodiments of the present disclosure provide a fast and efficient method to derive the rate controlling parameter and can be applied to generic perceptual audio encoders where low computational complexity is required.