Adaptive Audio Encoding with Noise Shaping and Variable Quantization
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Solution Overview
Problem
Existing audio signal encoding and decoding technologies face challenges in efficiently managing dynamic range variations and noise reduction, particularly in adaptive differential pulse code modulation (ADPCM) systems, where fixed filter coefficients and quantization step sizes can lead to suboptimal performance across varying signal conditions.
Innovation Solution
The implementation of an adaptive noise shaping filter and a variable rate quantizer with controlled step sizes, using a low-pass filter with determined coefficients and a predictor circuit with fixed FIR filter parameters, allows for dynamic adjustment of quantization steps and bit rates based on the frequency response of the low-pass filter, ensuring efficient encoding and decoding of audio signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed filter coefficients and quantization step sizes are used in ADPCM systems, then device complexity is reduced, but signal-to-noise ratio and prediction gain deteriorate under varying signal conditions
Solution Approach 1:
The patent implements adaptive noise shaping filters and variable rate quantizers that dynamically adjust filter coefficients and quantization step sizes based on the frequency response of the low-pass filter and signal characteristics. This allows the system to adapt to varying signal conditions, improving signal-to-noise ratio and prediction gain while maintaining manageable complexity through structured adaptation mechanisms.
Solution Approach 2:
The system changes parameters (filter coefficients and quantization step sizes) adaptively based on signal conditions. The adaptive quantizer modifies step sizes according to the frequency response characteristics, and the noise shaping filter adjusts its coefficients to optimize performance across different signal scenarios, resolving the contradiction between fixed simplicity and adaptive performance.
2Productivity
If adaptive quantization step sizes are implemented, then efficiency in varying dynamic range is improved, but device complexity increases
Solution Approach 1:
The adaptive quantizer dynamically adjusts step sizes based on the frequency response of the low-pass filter and signal characteristics. This dynamic adaptation improves encoding efficiency by optimizing quantization for varying dynamic ranges while the structured implementation keeps complexity manageable through systematic parameter adjustment rather than fully arbitrary adaptation.
3Measurement precision
If high sampling rates are used, then audio signal fidelity is improved, but bit rate and processing complexity increase
Solution Approach 1:
The system uses variable rate quantization that adapts the bit rate according to signal characteristics and frequency response. This allows high sampling rates to be used for maintaining fidelity when necessary, while the adaptive quantization efficiently reduces bit rate for less complex signal portions, balancing fidelity requirements with bit rate constraints.
Solution Approach 2:
The adaptive noise shaping filter selectively applies noise shaping only in frequency regions where it provides benefit, rather than uniformly across the entire spectrum. This partial application reduces unnecessary processing and bit rate while maintaining fidelity where it matters most, based on the frequency response characteristics of the low-pass filter.
Data Source
AI summary
An encoder includes a low-pass filter to filter input audio signals. The low-pass filter has fixed filter coefficients. The encoder generates quantized signals based on a difference signal. The encoder includes an adaptive quantizer and a decoder to generate feedback signals. The decoder has an inverse quantizer and a predictor. The predictor has fixed control parameters which are based on a frequency response of the low-pass filter. The predictor may include a finite impulse response filter having fixed filter coefficients. The decoder may include an adaptive noise shaping filter coupled between the low-pass filter and the encoder. The adaptive noise shaping filter flattens signals within a frequency spectrum corresponding to a frequency spectrum of the low-pass filter.