Adaptive Quantization Noise Filtering in Audio Decoding
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Solution Overview
Problem
Conventional audio encoding methods, such as AC-3 and E-AC-3, introduce audible pre-echo noise due to quantization, which existing quantization noise filtering techniques struggle to effectively address, especially when the decoder is not specially configured to apply the necessary filters.
Innovation Solution
An adaptive quantization noise filtering method is applied in the spectral domain to decoded audio signals, using signal-to-noise ratio values to determine filter gain values for each frequency band, reducing quantization noise more aggressively in bands with poorer signal quality and less in bands with better signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If quantization is applied during audio encoding to compress data, then data compression is improved, but audible pre-echo noise is introduced
Solution Approach 1:
The audio spectrum is divided into multiple frequency bands, and quantization noise filtering is applied independently to each band based on its signal-to-noise ratio. This segmentation allows selective filtering that preserves audio quality while removing noise.
Solution Approach 2:
Different filtering strengths are applied to different frequency bands based on their local signal-to-noise ratio characteristics. Bands with poor signal quality receive stronger filtering, while bands with better signal quality receive weaker filtering, optimizing the balance between noise reduction and audio preservation.
2Object-generated harmful factors
If conventional quantization noise filtering is applied to decoded audio signals, then quantization noise is reduced, but the decoder must be specially configured which increases device complexity
Solution Approach 1:
The filtering system uses the signal-to-noise ratio information already present in the decoded audio signal to automatically determine filtering parameters. The system self-adjusts the filtering strength based on the actual signal characteristics without requiring external configuration or special decoder settings.
Solution Approach 2:
The filtering parameters are dynamically changed based on the signal-to-noise ratio of each frequency band. This adaptive parameter adjustment allows the same decoder to effectively filter noise across varying audio content without special configuration.
3Object-generated harmful factors
If aggressive quantization noise filtering is applied to reduce noise, then noise suppression is improved, but damage to original audio content increases
Solution Approach 1:
The filtering strength is dynamically adjusted for each frequency band based on its signal-to-noise ratio. This dynamic adaptation ensures that filtering is applied only where necessary, preserving audio fidelity in clean bands while effectively suppressing noise in degraded bands.
Solution Approach 2:
Each frequency band receives a locally optimized filtering strength based on its specific signal-to-noise ratio characteristics. This local quality approach prevents over-filtering of clean audio content while providing sufficient noise suppression where needed.
Data Source
AI summary
A method including steps of decoding an encoded audio signal indicative of encoded audio content (e.g., audio content captured during a teleconference) to generate a decoded signal indicative of a decoded version of the audio content, and performing adaptive quantization noise filtering on the decoded signal. The filtering is performed adaptively in the frequency domain in response to data indicative of signal to noise values in turn indicative of a post-quantization signal-to-quantization noise ratio for each frequency band of each of at least one segment of the encoded audio content. In some embodiments, each signal to noise value is a bit allocation value equal to the number of mantissa bits of an encoded audio sample of a frequency band of a segment of the encoded audio content. Other aspects are decoder, or post-filter coupled to receive a decoder's output, configured to perform an embodiment of the adaptive filtering.