Speech Decoding Low-Pass Filter Bandwidth Sensitivity
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Solution Overview
Problem
In scalable coding schemes, adjusting the spectral tilt of the wideband region for improved encoding quality can degrade sound quality and lead to a perceived loss of bandwidth, especially in signals with high high-band energy, such as female voices.
Innovation Solution
A speech decoding method that applies a low-pass filter only to frames in the extension band region where abnormal sounds are likely, using adaptive filter coefficients based on the extension band energy ratio to minimize sound quality degradation and maintain bandwidth perception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-pass filter is applied to the bandwidth extension layer decoding signal to reduce slope of the spectrum, then the sound quality degradation is reduced, but the bandwidth sensitivity loss may occur due to attenuation of higher band region
Solution Approach 1:
The patent applies dynamics by making the low-pass filter application conditional rather than fixed. The filter is dynamically applied only to frames where the spectral slope exceeds a threshold value, allowing the system to adapt to varying signal characteristics and avoid unnecessary filtering that would cause bandwidth sensitivity loss.
Solution Approach 2:
The patent applies local quality by selectively applying the low-pass filter only to specific frequency regions and specific frames where needed. The spectral slope calculation identifies regions where filtering is necessary, and the filter is applied locally to those regions rather than uniformly across the entire spectrum, preserving bandwidth sensitivity in regions where it is not needed.
2Reliability
If the slope of the spectrum of the output signal is adjusted to improve sound quality, then the higher band region is attenuated, but bandwidth sensitivity is lost
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the filtering parameters based on the calculated spectral slope. When the slope exceeds a threshold, the low-pass filter is applied with specific parameters; when it does not exceed the threshold, filtering is avoided. This conditional parameter adjustment resolves the contradiction by adapting the filtering strength to the actual signal characteristics.
3Loss of information
If no low-pass filter is applied to maintain bandwidth sensitivity, then the slope of the spectrum remains steep, but sound quality degrades
Solution Approach 1:
The patent applies feedback by calculating the spectral slope of the bandwidth extension layer decoding signal and using this information to control the low-pass filter application. The spectral slope calculation provides feedback about the signal characteristics, and this feedback controls whether filtering is applied, creating a closed-loop system that resolves the contradiction between maintaining bandwidth sensitivity and improving sound quality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Prevents sound quality degradation and reduces the perceptibility of bandwidth loss by selectively applying low-pass filtering to frames with high extension band energy, maintaining the quality of the wideband signal.
Implementation Method 1
a low-pass filter having a moderate characteristic for an output signal instead of completely limiting the bandwidth of the above-described output signal and causes the high-band energy to attenuate
Data Source
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AI summary
The present invention pertains to a speech decoding device that is capable of preventing degradation in sound quality associated with an adjustment of the slope of a spectrum of an output signal (a decoding signal), making it less likely that a loss of bandwidth sensitivity due to the attenuation of a higher band region is perceived. For each frame of the bandwidth extension layer decoding signal, a filter assessment unit (304) determines whether or not to apply a low-pass filter to the bandwidth extension layer decoding signal on the basis of a change in energy in the bandwidth extension layer decoding signal. A low-pass filtering unit (306) filters the bandwidth extension layer decoding signal of the frames to which the low-pass filter is to be applied, as determined by the filter assessment unit (304), using the low-pass filter.