Audio Encoding Band Split for 7-8 kHz Recovery
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Solution Overview
Problem
Existing scalable coding techniques, such as those using ITU-T recommendation G.729.1, face challenges in encoding frequency components up to 8 kHz when limited to 7 kHz, leading to performance issues and increased calculation burdens due to the need for additional MDCT coefficient calculations.
Innovation Solution
The proposed solution involves a configuration that splits an input signal into lower and higher band components using QMF, suppresses the 7 to 8 kHz band in the lower band encoding section, and corrects the middle band component using low-pass filter characteristics to reconstruct and encode the lost band component, reducing calculation complexity and improving signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-pass filter is applied in the G.729.1 encoding section to limit frequency to 7 kHz, then the normal performance of the G.729.1 encoding section is secured, but the frequency components from 7 to 8 kHz are lost and cannot be encoded
Solution Approach 1:
The encoding system is divided into two independent encoding sections: the G.729.1 encoding section handles frequency components up to 7 kHz, while a separate encoding section handles the 7 to 8 kHz band. This segmentation allows each section to operate within its optimal frequency range without the low-pass filter blocking the higher frequencies, thus preserving all frequency information while maintaining G.729.1 performance.
2Loss of information
If the low-pass filter operation is stopped inside the G.729.1 encoding section to preserve 7 to 8 kHz components, then frequency information is retained, but the normal performance of the G.729.1 encoding section is not secured
Solution Approach 1:
The frequency spectrum is segmented into two bands: 0-7 kHz handled by G.729.1 encoding and 7-8 kHz handled by a separate encoding section. The G.729.1 section maintains its low-pass filter for optimal performance, while the separate section captures the higher frequency components that would otherwise be lost, achieving both performance and information preservation.
3Loss of information
If MDCT calculation is performed on the signal of 0 to 8 kHz band to calculate frequency components of the 7 to 8 kHz band, then the lost band component can be recovered, but the amount of calculations increases significantly
Solution Approach 1:
Instead of performing MDCT on the entire 0-8 kHz signal, the system segments the frequency spectrum and processes different bands separately. The G.729.1 section processes 0-7 kHz using its optimized algorithms, while a separate section handles 7-8 kHz, avoiding the need for full-band MDCT calculations and reducing overall computational complexity.
Solution Approach 2:
The system performs partial MDCT calculations only on the necessary frequency bands rather than the entire spectrum. By calculating MDCT coefficients only for the specific 7-8 kHz band needed, rather than recalculating for the entire 0-8 kHz range, the computational burden is significantly reduced while still recovering the lost frequency components.
Data Source
AI summary
Provided is an encoding device which divides an input signal into a low-range component and a high-range component and encodes the components in separate encoding units. The encoding device can improve quality of a decoded signal. The encoding device (101) includes: a band division process unit (201) which subjects an input signal to a band division process so as to obtain a lower intermediate-range component lower than a first frequency and a high-range component higher than the first frequency; a low-range encoding unit (202) which suppresses a portion of the lower intermediate-range component higher than a second frequency so as to obtain a low-range component and encodes the low-range component so as to obtain low-range encoded information; an intermediate-range correction unit (203) corrects the intermediate-range component higher than the second frequency among the suppressed lower intermediate-range component so as to obtain a corrected intermediate-range component; an intermediate high-range encoding unit (204) which encodes the corrected intermediate-range component and the high-range component so as to obtain intermediate high-range encoded information; and a multiplexing unit (205) which multiplexes the low-range encoded information and the intermediate high-range encoded information so as to obtain encoded information.