Undetectable DAB FM Signal Blending via Time Alignment
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Solution Overview
Problem
Existing methods for seamlessly switching between DAB and FM signals during simulcast transmissions often result in audio discontinuities due to lack of time, level, and frequency alignment, with current solutions being either computationally intensive or causing noticeable audio degradation.
Innovation Solution
Implementing an efficient method for time, level, and frequency response alignment between DAB and FM signals using optimized signal processing techniques, including asynchronous sample rate conversion, gain matching, and cross-correlation for delay compensation, to ensure seamless blending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If sample correlation time alignment is performed to align DAB and FM signals, then audio quality is improved, but computational complexity increases significantly
Solution Approach 1:
The patent performs preliminary time alignment by calculating the correlation between DAB and FM signals to determine a time offset, then applies this offset to pre-align the signals before blending. This preliminary action avoids the need for continuous complex computations during switching, reducing real-time computational complexity while maintaining alignment precision.
Solution Approach 2:
Instead of performing full sample-by-sample correlation continuously, the patent applies partial correlation by determining the time offset once or periodically and using this offset for alignment. This partial action approach achieves sufficient alignment precision without the excessive computational burden of continuous full correlation.
2Device complexity
If simple switching is used to switch between DAB and FM signals, then device complexity is reduced, but audio continuity deteriorates due to misalignment
Solution Approach 1:
The patent performs preliminary time alignment by calculating the correlation between DAB and FM signals to determine a time offset, then applies this offset to pre-align the signals before blending. This preliminary action avoids the need for continuous complex computations during switching, reducing real-time computational complexity while maintaining alignment precision.
Solution Approach 2:
The patent introduces a time offset calculation as an intermediary step between simple switching and full correlation alignment. This intermediary approach computes the time difference once and uses it to guide the blending process, maintaining audio continuity without requiring complex continuous adjustments.
3Device complexity
If signals are mixed and ramped without time alignment, then device complexity is reduced, but audio quality deteriorates due to confused audio during ramping
Solution Approach 1:
The patent performs preliminary time alignment by calculating the correlation between DAB and FM signals to determine a time offset, then applies this offset to pre-align the signals before blending. This preliminary action avoids the need for continuous complex computations during switching, reducing real-time computational complexity while maintaining alignment precision.
Data Source
AI summary
The approach shown provides for an efficient implementation of time response, level response and frequency response alignment between two audio sources such as DAB and FM that may be time offset from each other by as much as 2 seconds, and produces an aurally undetectable transition between the sources. Computational load is significantly reduced over the approaches known in the prior art.