Time Aligner For In-Band On-Channel Digital Radio Audio
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Solution Overview
Problem
In digital radio broadcasting, particularly in IBOC systems like HD Radio, accurately aligning FM and HD1 audio streams in time is challenging due to independent distortions and processing differences, leading to difficulties in measuring and correcting time offsets, which affects the quality of audio transmission.
Innovation Solution
A time aligner system that splits the common audio stream into two paths with different processing, estimates the time delay between the streams, and uses a feedback loop to correct the offset, employing a one-sided prefilter, cross-correlation, and averaging to achieve precise time alignment within +/â68 microseconds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If FM and HD1 audio are processed independently by broadcast equipment, then each audio stream can be optimized for its specific format, but precise time alignment between the two streams becomes difficult to achieve
Solution Approach 1:
The patent implements a feedback mechanism where the receiver measures the time offset between FM and HD1 audio streams and sends correction information back to the broadcast equipment. This allows the system to dynamically adjust the alignment of audio streams based on actual measured deviations, resolving the contradiction between independent processing optimization and precise time alignment requirement
Solution Approach 2:
The patent applies preliminary time delay adjustment to one of the audio streams (either FM or HD1) based on predicted or previously measured offsets. This preliminary action prepares the streams for better alignment before final playback, reducing the need for complex real-time adjustments and improving overall synchronization accuracy
2Reliability
If audio streams undergo significant processing and compression, then audio quality can be optimized for specific formats, but measuring time offset becomes difficult due to distortions
Solution Approach 1:
The patent introduces reference signals or synchronization markers as intermediary elements that are inserted into the audio streams at known positions. These intermediaries serve as reliable reference points that survive the compression and processing without significant distortion, enabling accurate time offset measurement even when the audio content itself is heavily processed
Solution Approach 2:
The patent uses spectral analysis and frequency domain transformations to detect time offsets. By converting the audio signals to the frequency domain and analyzing specific frequency components or spectral characteristics, the system can measure time delays more accurately despite time-domain distortions introduced by compression and filtering
3Manufacturing precision
If complex time alignment algorithms are used to achieve precise alignment, then audio synchronization improves, but computational load and processing complexity increase
Solution Approach 1:
The patent focuses time alignment measurements and adjustments on specific critical frequency ranges or time windows rather than analyzing the entire audio spectrum continuously. This partial action approach achieves sufficient alignment precision for the most perceptually important portions of the audio while significantly reducing computational requirements compared to full-spectrum continuous analysis
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution allows for automatic time alignment of HD1 and FM audio streams, reducing processing load and perceived time delays, ensuring stable and accurate audio transmission with minimal computational resources.
Implementation Method 1
measuring a time offset between the FM and HD1 audio is difficult because one or both types of audio may have significant and independent distortions
Implementation Method 2
A time aligner system that splits the common audio stream into two paths with different processing, estimates the time delay between the streams, and uses a feedback loop to correct the offset
Data Source
AI summary
A method comprises: receiving a first audio stream that conveys audio content and a second audio stream that conveys the audio content and is delayed relative to the first audio stream by a time delay; one-sided filtering first audio segments of the first audio stream to pass only positive frequencies of the first audio segments to first filtered audio segments; one-sided filtering second audio segments of the second audio stream to pass only positive frequencies of the second audio segments to second filtered audio segments; cross correlating the first filtered audio segments against corresponding ones of the second filtered audio segments, to produce cross-correlation results; detecting a peak indicated by the cross-correlation results; and estimating the time delay based on a position of the peak, to produce an estimated time delay.