Adaptive Voice Spectrum Compression for Narrowband Speech
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Solution Overview
Problem
Conventional voice communication systems suffer from limited bandwidth, leading to degraded sound quality and loss of high-frequency components, which results in unnatural voice reproduction and poor intelligibility, especially in digital speech communications where bandwidth restrictions further exacerbate the issue.
Innovation Solution
A voice emphasis device that includes a time-to-frequency converter, input signal analyzer, band determinator, spectrum compressor, and frequency-to-time converter to dynamically adjust the boundary frequency based on the input signal mode, allowing for optimal compression and synthesis of high-frequency components within the passband, thereby preventing strange sounds and enhancing voice quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the frequency band is limited to 3,400 Hz or lower in conventional telephone systems, then the transmission bandwidth is reduced and bit rate is controlled, but the sound quality and intelligibility of voice signals are degraded due to loss of high-frequency components
Solution Approach 1:
The patent applies dynamics by making the boundary frequency adaptive rather than fixed. The boundary frequency is dynamically adjusted based on the analysis of input signal mode (vowel, consonant, or noise) to optimally reflect high-frequency components within the passband while maintaining sound quality and intelligibility
Solution Approach 2:
The patent changes the parameter of boundary frequency based on signal characteristics. By analyzing the input signal mode and adjusting the boundary frequency accordingly, the system optimizes the reflection of high-frequency components to improve sound quality without requiring increased transmission bandwidth
2Device complexity
If high-frequency components are compressed and reflected in a fixed predetermined band, then the processing is simple, but the sound quality degrades when the predetermined band is not optimal for the input signal mode
Solution Approach 1:
The patent transforms the fixed predetermined band into a dynamic adaptive band. The boundary frequency is adjusted according to the analyzed input signal mode (vowel, consonant, or noise), allowing the system to maintain high sound quality across different speech conditions without excessive processing complexity
Solution Approach 2:
The system performs self-adjustment by analyzing its own input signal characteristics and automatically determining the optimal boundary frequency. The input signal analyzer examines the signal mode and the band determinator selects appropriate boundary frequencies, enabling the system to optimize its own performance without external intervention
Data Source
AI summary
An input signal analyzer determines a boundary frequency within the limit of a range which does not exceed a first frequency from the mode of an input signal. A spectrum compressor compresses a power spectrum of frequencies in a band higher than the first frequency in a frequency direction. A gain corrector performs a gain correction on the compressed power spectrum. A spectrum synthesizer reflects the power spectrum outputted from the gain corrector in a band determined by both the first frequency and the boundary frequency. A frequency-to-time converter converts both a synthesized power spectrum provided by the spectrum synthesizer and a phase spectrum of the input signal into ones in the time domain, and outputs these spectra.