Variable Rate Speech Coder Frame Reallocation
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Solution Overview
Problem
Current speech coders operating at low bit rates, such as 2.4 to 4 kbps, face challenges in maintaining high voice quality due to limited bit rates, leading to perceptually significant distortions like noise and buzz, and are limited to fixed average output rates, restricting their flexibility and performance.
Innovation Solution
Implementing a method to achieve arbitrary average data rates by reallocating frames between different component rates within a set of pre-determined composite rates, allowing for continuous variable output rates rather than fixed rates, thereby enhancing flexibility and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If speech coders operate at low bit rates (2.4 to 4 kbps), then bandwidth efficiency is improved, but voice quality deteriorates due to perceptually significant distortions like noise and buzz
Solution Approach 1:
The patent implements variable rate coding where the speech coder can dynamically adjust the output bit rate based on the complexity of the speech signal. The system switches between different coding modes (e.g., full rate, half rate, quarter rate) depending on the analysis of the input speech, allowing optimal quality-for-bitrate performance rather than operating at a fixed low rate that causes distortions.
Solution Approach 2:
The system changes the operating parameters (bit rate, coding mode) based on the characteristics of the input speech signal. By analyzing the speech and adjusting the coding parameters in real-time, the system maintains high voice quality while achieving low average bit rates, resolving the contradiction between bandwidth efficiency and voice quality.
2Device complexity
If speech coders use fixed average output rates, then implementation simplicity is improved, but flexibility and performance are limited
Solution Approach 1:
The patent transforms the fixed-rate system into a dynamic variable-rate system that automatically adjusts the output bit rate based on the input speech characteristics. This provides flexibility in adapting to different speech conditions while maintaining relatively simple implementation through automated rate control mechanisms.
Solution Approach 2:
The system incorporates feedback mechanisms where the output bit rate is adjusted based on the actual speech analysis results. This feedback loop enables the system to adapt to varying speech complexity and maintain optimal performance without requiring complex manual configuration, thus achieving flexibility with moderate implementation complexity.
3Adaptability or versatility
If the number of average data rates is increased, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent segments the coding system into discrete coding modes (e.g., full rate mode, half rate mode, quarter rate mode) rather than implementing a continuous range of rates. This segmentation provides a manageable set of predefined rates that can be switched between based on speech characteristics, achieving high adaptability without the complexity of implementing every possible rate or using complex rate control algorithms.
Data Source
AI summary
Methods and apparatus are provided for achieving an arbitrary average data rate for a variable rate coder. One method includes selecting a set (e.g., a pair) of initial composite rates surrounding the arbitrary average data rate. A reallocation fraction is then calculated based on the initial composite rates. The reallocation fraction is used to reassign a number of frames from one component rate of an initial composite rate to another in order to achieve the arbitrary average data rate. Such a method may be configured such that selecting an initial composite rate on one side of (e.g., less than) the arbitrary average data rate implicitly selects the initial composite rate on the other side of the arbitrary average data rate.