Audio Signal Requantization for Low-Noise Bit-Depth Extension
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Solution Overview
Problem
Conventional digital audio technologies struggle to accurately recreate minute and low-frequency signals due to quantization noise, leading to unclear sound quality and the need for multiple low-pass filters with different cutoff characteristics, which increases processing complexity and limits the ability to handle various signal types effectively.
Innovation Solution
An audio signal processing apparatus that extends the bit count of digital signals by generating a change signal with a fixed quantization width, smoothing it using a second quantization width, and adding a difference signal to produce an output signal, allowing for bit width extension without increasing processing scale through multiple low-pass filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple low-pass filters with different cutoff characteristics are provided to handle various signal types, then adaptability to different signals is improved, but device complexity increases
Solution Approach 1:
The patent implements a single low-pass filter that can adaptively adjust its cutoff frequency based on the input signal characteristics. The filter serves multiple functions by dynamically changing its parameters, eliminating the need for multiple dedicated filters for different signal types while maintaining high adaptability.
Solution Approach 2:
The low-pass filter is designed with dynamic cutoff frequency adjustment capability. The cutoff frequency changes adaptively according to the signal characteristics, allowing the same filter structure to handle various signal types effectively without requiring multiple static filters.
2Measurement precision
If conventional bit extension technique is used to extend quantization bit number, then quantization noise is reduced, but high-frequency components are lost due to low-pass computation
Solution Approach 1:
The low-pass filter cutoff frequency is dynamically adjusted based on the signal characteristics. By adapting the cutoff frequency to the actual signal content, the filter preserves high-frequency components that are relevant to the signal while still achieving smooth interpolation and reducing quantization noise, thus preventing unnecessary high-frequency loss.
Solution Approach 2:
The patent changes the filter parameters (cutoff frequency) according to the signal characteristics. This parameter adaptation allows the filter to optimize its performance for different signal types, maintaining quantization precision while preserving important high-frequency information that would otherwise be lost with fixed low-pass filtering.
Data Source
AI summary
Audio signal processing apparatus includes: an amplitude change extractor 3 which obtains an amplitude change extraction signal which is a signal having an amplitude changing at a fixed quantization width when an amplitude of an input signal temporally changes; a first requantizer 2 which extends, from a first bit count to a second bit count, a bit count representing the amplitude change extraction signal obtained; a second requantizer 5 which smoothes the amplitude change extraction signal by requantizing using a second quantization width less than a first quantization width used on the input signal; a difference signal generator which obtains a difference signal which is a signal represented using the second bit count and obtained by subtracting the amplitude change extraction signal from the input signal; and an adder 6 which generates an output signal by adding a second requantized signal which is the amplitude change extraction signal smoothed by the second requantizer 5 and the difference signal obtained by the difference signal generator 4.