Audio Subband Window Interpolation for Low-Aliasing Filterbanks
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Solution Overview
Problem
Modern digital audio processing systems face challenges in balancing bit rate, computational complexity, memory requirements, quality, and delay, particularly in real-time applications, where compromises often need to be made across these parameters.
Innovation Solution
The use of an interpolation scheme to derive a window function with a smaller number of window coefficients from a larger one, improving the distribution of energy values and reducing aliasing, while maintaining quality and reducing memory usage, is employed in both analysis and synthesis filterbanks to achieve a better trade-off between delay and quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a larger window function with more coefficients is used, then audio quality is improved, but memory requirements increase
Solution Approach 1:
The patent segments the audio signal into subbands using filterbanks, allowing processing of smaller portions of the signal at a time. This segmentation enables the use of smaller window functions within each subband while maintaining overall audio quality, thereby reducing memory requirements compared to processing the entire signal with a large window function.
Solution Approach 2:
The patent changes the parameter of window function size by using different window sizes for different subbands. Instead of uniformly using a large window function across all frequencies, the system adapts the window size to the specific subband being processed, optimizing the balance between audio quality and memory usage.
2Measurement precision
If a larger window function is used, then audio quality is improved, but processing delay increases
Solution Approach 1:
By segmenting the audio signal into multiple subbands, the patent enables parallel processing of smaller signal portions. Each subband can be processed with a smaller window function, reducing the processing delay while maintaining audio quality through the combined reconstruction of all subbands.
Solution Approach 2:
The patent applies partial action by processing only the necessary portion of the signal at each stage. Instead of waiting to accumulate enough data for a large window function, the system processes smaller subband portions independently and combines them, achieving quality results with reduced delay.
3Loss of time
If a smaller window function is used, then processing delay is reduced, but audio quality deteriorates
Solution Approach 1:
The patent compensates for using smaller window functions by segmenting the signal into multiple subbands. The combination of multiple subband transformations maintains audio quality even though each individual subband uses a smaller window function with reduced delay.
Solution Approach 2:
The patent merges the results from multiple subband processing operations to reconstruct the full audio signal. By combining the transformed subbands, the system achieves audio quality comparable to using a single large window function, while benefiting from the reduced delay of smaller individual window operations.
4Object-generated harmful factors
If more window coefficients are used, then aliasing is reduced, but computational complexity increases
Solution Approach 1:
The patent reduces aliasing by segmenting the signal into subbands and applying appropriate filtering to each. This segmentation allows the use of computationally efficient filter structures that effectively suppress aliasing without requiring excessively large window functions, thus balancing aliasing reduction with computational complexity.
Solution Approach 2:
The patent optimizes the window function parameters by using different window sizes and types for different subbands. This adaptive parameter selection reduces aliasing in each subband while minimizing the overall computational complexity compared to using a uniformly large window function across all frequencies.
Data Source
AI summary
An embodiment of an apparatus for generating audio subband values in audio subband channels includes an analysis windower for windowing a frame of time-domain audio input samples being in a time sequence extending from an early sample to a later sample using an analysis window function including a sequence of window coefficients to obtain windowed samples. The analysis window function includes a first number of window coefficients derived from a larger window function including a sequence of a larger second number of window coefficients, wherein the window coefficients of the window function are derived by an interpolation of window coefficients of the larger window function. The apparatus further includes a calculator for calculating the audio subband values using the windowed samples.