Tonality-Adaptive Audio Quantization for Musical Noise Reduction
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Solution Overview
Problem
In very-low-bit-rate audio coding, musical noise artifacts occur due to insufficient bit allocation, particularly in stationary music or noise spectra, where transform lines are quantized to zero or not, leading to a tonal character in the decoded signal and inefficient bit usage, especially at low frequencies where the human auditory system is sensitive.
Innovation Solution
An audio encoder with a signal-adaptive dead-zone quantization scheme that modifies the dead-zone based on tonality indicating values for spectral lines or groups, allowing for per-bin or per-band dead-zone selection before quantization, reducing complexity and side-information requirements, and optimizing audio quality by varying the dead-zone size based on frequency and tonality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed dead-zone quantization is used, then the encoding complexity is low, but musical noise artifacts occur and audio quality deteriorates
Solution Approach 1:
The patent applies dynamics by making the dead-zone size adaptive rather than fixed. The quantizer modifies the dead-zone size based on the instantaneous characteristics of the input signal, specifically adapting to tonal versus non-tonal spectral regions. This dynamic adjustment reduces musical noise artifacts while maintaining manageable encoding complexity through efficient signal analysis methods.
Solution Approach 2:
The patent changes the parameter of dead-zone size based on signal characteristics. By analyzing tonality indicators and adjusting the dead-zone parameter accordingly, the system achieves better audio quality by preventing musical noise in non-tonal regions while preserving tonal components, without requiring complex encoding structures.
2Object-generated harmful factors
If the dead-zone is adapted on the entire spectrum, then musical noise is reduced, but bit-rate increases due to side-information transmission
Solution Approach 1:
The patent applies local quality by adapting the dead-zone on a per-frequency-band basis rather than uniformly across the entire spectrum. Each frequency band can have its own optimized dead-zone size based on local signal characteristics, which reduces musical noise in specific regions without requiring transmission of side-information for the entire spectrum, thereby controlling bit-rate.
Solution Approach 2:
The patent segments the spectrum into multiple frequency bands and applies independent dead-zone adaptation to each band. This segmentation allows selective adaptation where needed while avoiding unnecessary side-information transmission in other regions, effectively reducing musical noise while maintaining efficient bit-rate usage.
3Object-generated harmful factors
If per-frequency-band dead-zone adaptation is used, then musical noise is reduced, but encoding complexity increases due to multiple quantization attempts
Solution Approach 1:
The patent applies preliminary action by calculating tonality indicators and determining optimal dead-zone sizes for each frequency band before performing quantization. This pre-calculation approach eliminates the need for multiple quantization attempts and subsequent comparisons, reducing encoding complexity while still achieving effective musical noise reduction through adaptive dead-zone adjustment.
Data Source
AI summary
The invention provides an audio encoder for encoding an audio signal so as to produce therefrom an encoded signal, the audio encoder including: a framing device configured to extract frames from the audio signal; a quantizer configured to map spectral lines of a spectrum signal derived from the frame of the audio signal to quantization indices, wherein the quantizer has a dead-zone, in which the input spectral lines are mapped to quantization index zero; and a control device configured to modify the dead-zone; wherein the control device includes a tonality calculating device configured to calculate at least one tonality indicating value for at least one spectrum line or for at least one group of spectral lines, wherein the control device is configured to modify the dead-zone for the at least one spectrum line or the at least one group of spectrum lines depending on the respective tonality indicating value.