Subband Coding Spectral Inversion for Mirror Image Correction

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Solution Overview

Problem

Subband coding techniques using QMF filters generate mirror image spectra in the high band, leading to deteriorated coding performance and sound quality when encoding wideband speech signals.

Innovation Solution

A subband coding apparatus that includes a band dividing section, frequency domain transforming section, spectrum rearranging section, and coding section to reverse the order of spectral components in the high band spectrum, preventing aliasing and improving encoding efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If subband coding uses QMF filters to divide wideband signals into low and high bands, then the coding complexity is reduced and processing efficiency is improved, but mirror image spectrum distortion is generated in the high band leading to deteriorated coding performance

Engineering Contradiction:

Improvecoding efficiencyVSAvoidspectral accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent applies spectral inversion by multiplying the high band spectrum by (-1)^k where k is the frequency index. This inversion operation reverses the mirror image distortion caused by QMF filtering, transforming the distorted spectrum back into its correct form and thereby resolving the spectral accuracy degradation while preserving the coding efficiency benefits of subband processing

Inventive Principle:

Principle #13The other way round (Inversion)

2Quantity of substance

If the high band signal is down-sampled by a factor of 2 after QMF filtering, then the total bit rate is reduced, but aliasing distortion occurs generating mirror image spectrum

Engineering Contradiction:

Improvebit rateVSAvoidaliasing distortion

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful aliasing distortion into a beneficial correction opportunity by applying spectral inversion. The mirror image spectrum generated by down-sampling is not merely corrected but systematically inverted using (-1)^k multiplication, transforming the distortion artifact into a recoverable pattern that restores spectral accuracy while maintaining the low bit rate advantage

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS8103516B2Subband coding apparatus and method of coding subband

Publication Date: 2012.01.24 III HOLDINGS 12 LLC

AI summary

A subband coding apparatus carries out subband coding which prevents deterioration in coding performance and improves audio quality of decoded signals. The subband coding apparatus includes a low-band coding section (103) to code a low-band spectrum (S13). A low-band decoding section (106) decodes a low-band coded data (S14) and outputs a decoded low-band spectrum (S18) to a high-band coding section (107). A spectrum rearranging section (105) rearranges to make each frequency component of a high-band spectrum (S16) in reverse order on the frequency axis and outputs a modified high-band spectrum (S17) after rearranging to a high-band coding section (107). The high-band coding section (107) uses the decoded low-band spectrum (S18) output from the low-band decoding section (106) to code the modified high-band spectrum (S17) output from the spectrum rearranging section (105).