HDMI Audio Clock Extraction for Low-Jitter Playback
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Solution Overview
Problem
Conventional HDMI interfaces face sound quality deterioration due to audio clock jitter, as they transfer audio and video signals in synchronization with a video clock, and existing solutions with separate HDMI outputs for audio and video do not adequately suppress jitter.
Innovation Solution
A reproducing apparatus that generates a second video clock signal based on the audio clock signal, with specific parameters (CTS2 and N2) set to ensure the frequency ratio is an integer, reducing jitter and improving sound quality by outputting the second video clock and audio signals without the audio clock signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the audio clock signal is transferred via PLL based on video clock synchronization, then the HDMI interface can transfer high-bit-rate audio signals, but audio clock jitter occurs causing sound quality deterioration
Solution Approach 1:
The invention extracts the audio clock signal from the video clock synchronization system by providing a dedicated audio clock output terminal that directly outputs the audio clock signal without passing through the PLL circuit. This separates the audio clock transfer path from the video synchronization path, eliminating the jitter introduced by PLL while maintaining high-bit-rate audio transmission capability.
2Reliability
If parameters N and CTS are controlled to reduce PLL jitter, then sound quality improves slightly, but sufficient jitter suppression is not achieved
Solution Approach 1:
The invention extracts the audio clock signal from the video clock synchronization system by providing a dedicated audio clock output terminal that directly outputs the audio clock signal without passing through the PLL circuit. This separates the audio clock transfer path from the video synchronization path, eliminating the jitter introduced by PLL while maintaining high-bit-rate audio transmission capability.
3Reliability
If video signals are made completely black in audio-exclusive HDMI output, then video signals are prevented from disturbing audio signals, but the solution is still insufficient for jitter suppression
Solution Approach 1:
The invention segments the HDMI output into separate functional paths: a video-exclusive output for video signals and an audio-exclusive output for audio signals with dedicated audio clock output. This segmentation allows independent optimization of each path, enabling direct audio clock transfer without PLL in the audio path while maintaining video synchronization in the video path.
Data Source
AI summary
According to the present invention, the sound quality of an apparatus having HDMI outputs exclusive for both of an audio signal and a video signal can be further improved. According to the present invention, even when the calculated value of CTS obtained using a first video clock signal Vc1 generated by a decoder 204 is other than an integer, a value of a second video clock signal Vc2 and an N value are set such that the calculated value of CTS obtained using the second video clock signal Vc2 is an integer. By using the value of second video clock signal Vc2 and the N value set in this manner, an audio reproducing apparatus 103 can generate an audio clock signal Ac having reduced jitter.