Direct-Diffuse Audio Bandwidth Extension for Compression Artifacts
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Solution Overview
Problem
Conventional methods for enhancing compressed audio signals, such as bandwidth extension and equalization, fail to effectively restore original audio quality due to difficulties in detecting high-frequency cut-off frequencies and addressing 'holes' in the spectrogram that create audible artifacts and loss of sound attacks.
Innovation Solution
An audio signal processing apparatus and method that decompose input audio signals into direct and diffuse components, with a bandwidth extender and combiner to enhance the direct audio signal by extending its frequency range and combining it with the diffuse signal, using upmixing, equalization, and reverberation techniques to improve perceptual quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bandwidth extension techniques are used to restore high frequencies, then high-frequency components are regenerated, but the detection of actual high-frequency cut-off frequency is difficult and inaccurate
Solution Approach 1:
The audio signal is segmented into direct sound components and diffuse sound components. The bandwidth extender is applied selectively only to the direct sound portion, which contains the relevant high-frequency information, while the diffuse sound (ambient/reverberant field) is preserved without high-frequency extension. This segmentation approach avoids the complexity of analyzing the entire mixed signal for cut-off frequency detection.
Solution Approach 2:
An intermediary processing stage is introduced that separates the compressed audio signal into direct and diffuse components before applying bandwidth extension. This intermediary separation allows for more accurate and simpler cut-off frequency detection in the direct sound portion, where the spectral characteristics are clearer and more reliable.
2Object-affected harmful factors
If conventional bandwidth extension is applied to the whole signal, then high frequencies are restored, but audible artifacts such as musical noise and birdie sounds are created due to holes in the spectrogram
Solution Approach 1:
The audio signal is divided into direct sound and diffuse sound segments. Bandwidth extension is applied only to the direct sound segment, which contains the primary audio information and fewer spectral holes. The diffuse sound segment, which already contains ambient noise and reverberation, is left unmodified, preventing the creation of audible artifacts like musical noise and birdie sounds that would result from extending frequencies in the already-noisy diffuse portion.
Solution Approach 2:
Different processing quality is applied to different portions of the audio signal. The direct sound receives high-quality bandwidth extension processing to restore lost high frequencies, while the diffuse sound maintains its original characteristics without high-frequency extension, avoiding the introduction of artifacts in regions where high-frequency content is less perceptually critical.
3Ease of operation
If equalization techniques are used to improve perceived quality, then general sound effects are enhanced, but the loss of sound attacks and transient details is not addressed
Solution Approach 1:
The audio signal is segmented into direct sound containing transient information and diffuse sound containing ambient information. The modifier processes the direct sound to restore transient details and attacks that were lost during compression, while the diffuse sound is preserved to maintain the ambient atmosphere. This segmentation allows targeted restoration of transient information without compromising the overall perceptual quality enhancement.
Data Source
AI summary
Example audio signal processing apparatuses and methods for processing an input audio signal into an output audio signal are disclosed. An example audio signal processing apparatus comprises a decomposer configured to decompose the input audio signal into a direct audio signal and a diffuse audio signal, a modifier configured to modify the direct audio signal in order to obtain a modified direct audio signal, wherein the modifier comprises a bandwidth extender configured to extend an upper cutoff frequency of a frequency range of the direct audio signal, and a combiner configured to combine the modified direct audio signal with the diffuse audio signal to obtain the output audio signal.