Time Alignment of Analog and Digital Audio Pathways
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Solution Overview
Problem
Existing methods for time alignment between analog and digital pathways in digital radio receivers require a large number of multiply operations and significant memory, making them inefficient and prone to audio distortions during signal transitions.
Innovation Solution
A method involving downsampled audio streams is used, where a correlator performs cross-correlation on decimated samples to determine the time offset, allowing for adjustments through sample rate converters or pointer adjustments, achieving desired accuracy with reduced computational load and memory usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cross-correlation is performed on full-resolution audio streams to determine time alignment, then measurement precision is improved, but computational complexity and memory requirements increase significantly
Solution Approach 1:
The patent divides the audio signal processing into two stages: first processing downsampled/decimated versions of the audio streams to obtain a coarse time offset estimate, then using this estimate to guide a second cross-correlation on the full-resolution streams within a reduced search window. This segmentation of the correlation process into coarse and fine stages reduces overall computational complexity while maintaining alignment accuracy.
Solution Approach 2:
The patent performs preliminary downsampling and initial cross-correlation on decimated audio streams before processing the full-resolution streams. This preliminary action provides an initial time offset estimate that narrows the search range for the subsequent full-resolution correlation, significantly reducing the number of operations required while preserving measurement precision.
2Measurement precision
If cross-correlation is performed on full-resolution audio streams to determine time alignment, then measurement precision is improved, but memory requirements increase significantly
Solution Approach 1:
The patent segments the memory-intensive cross-correlation operation into two phases: a first phase using downsampled streams that requires minimal memory, and a second phase that processes only a limited window of full-resolution samples around the estimated offset. This segmentation dramatically reduces peak memory requirements while maintaining alignment precision.
Solution Approach 2:
The preliminary cross-correlation on decimated streams is performed first to obtain an offset estimate, which then defines a narrow search window for the full-resolution correlation. This preliminary action prevents the need to load and process entire high-resolution audio streams into memory simultaneously, reducing memory requirements while preserving measurement accuracy.
3Device complexity
If time alignment is not properly achieved between analog and digital pathways, then device complexity is reduced, but audio quality and reliability deteriorate due to distortions during signal transitions
Solution Approach 1:
The patent implements a feedback mechanism where the cross-correlation operation continuously monitors the alignment between analog and digital audio streams and provides offset estimates that are used to adjust the timing of one pathway relative to the other. This closed-loop feedback ensures reliable audio quality during transitions while maintaining manageable device complexity through efficient correlation algorithms.
Solution Approach 2:
The patent employs dynamic processing where the correlation window and processing parameters are adjusted based on the estimated offset and signal characteristics. This dynamic approach maintains high audio quality during transitions by adapting the alignment process to current conditions, while keeping device complexity manageable through selective processing only when needed.
Data Source
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AI summary
A method for processing a radio signal includes producing first and second streams of audio samples; decimating the first and second streams of audio samples to produce first and second streams of decimated streams of audio samples; estimating a first offset value between corresponding samples in the first and second streams of decimated streams of audio samples; shifting one of the first and second streams of audio samples by a first shift value; decimating the first and second streams of audio samples to produce third and fourth streams of decimated audio samples; estimating a second offset value; determining a final offset value based on an intersection of ranges of valid results of the first and second offset values; and shifting one of the first and second streams of audio samples by the final offset value to align the first and second streams of audio samples.