Audio Loopback Clock Synchronization for HDMI ARC
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Solution Overview
Problem
Audio data received over HDMI ARC or eARC interfaces can experience temporary loss or discontinuities in sampling clocks when switching between multiple audio sources, leading to degradation in the user's listening experience due to popping sounds and other audio issues.
Innovation Solution
A media device substitutes an externally generated clock derived from a local crystal oscillator for missing sampling clocks, synchronizing it with the input clock, and inserts zero padding to mitigate discontinuities, while also handling format conversion and decoding of audio data for wireless or wired transmission to audio playback devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the media device receives audio data from multiple audio sources over ARC or eARC interface, then the audio data can be sourced from various devices (Internet, Blu-ray players, etc.), but temporary loss or discontinuities in sampling clocks may occur when switching between sources, resulting in popping sounds and degradation in listening experience
Solution Approach 1:
The patent introduces an intermediary clock generation mechanism that creates a local clock signal when external sampling clocks are unavailable. This intermediary clock acts as a mediator between the audio data stream and the playback device, ensuring continuous operation without popping sounds. The local clock is synchronized with the audio data format parameters (sampling rate, bit depth) to maintain signal integrity during source transitions.
Solution Approach 2:
The system performs preliminary synchronization of the local clock with the external sampling clock before the external clock fails. By anticipating clock discontinuities and pre-synchronizing the local oscillator, the system ensures seamless transition without audible artifacts. This preliminary action prepares the clock system in advance for potential source switching events.
2Reliability
If the media device substitutes an externally generated clock for missing sampling clocks, then clock continuity can be maintained, but additional processing steps (synchronization, zero padding) are required
Solution Approach 1:
The system implements self-service by automatically detecting clock discontinuities and triggering local clock generation without external intervention. The media device monitors the incoming audio data stream for clock presence and autonomously switches between external and internal clock sources. This self-service approach simplifies the overall system architecture by eliminating the need for complex external clock distribution infrastructure.
Solution Approach 2:
The patent utilizes parameter changes in the audio data format (sampling rate, bit depth, channel configuration) to synchronize the local clock with the incoming stream. By dynamically adjusting the local oscillator parameters based on the audio format metadata, the system achieves clock synchronization without requiring complex phase-locked loop circuits or external reference signals.
3Object-affected harmful factors
If the media device buffers audio data and inserts zero padding during clock transitions, then popping sounds can be prevented, but latency may increase
Solution Approach 1:
The system applies partial buffering, storing only the minimum necessary audio samples required to smooth clock transitions. Instead of buffering entire audio frames or seconds of data, the patent buffers just enough samples to cover the clock switch-over period. This partial action approach prevents popping sounds while minimizing latency introduction, striking an optimal balance between audio quality and real-time performance.
Solution Approach 2:
The patent implements rapid clock switching with minimal buffering by rushing through the transition period. When an external clock fails, the system quickly switches to the local clock with a brief buffer period, rather than maintaining extended buffering. This skipping approach minimizes the time audio data spends in the buffer, reducing latency while still preventing audible artifacts during the brief transition window.
Data Source
AI summary
A system and method to process audio data received over the ARC or eARC interface of HDMI from audio sources are provided. A media device may receive compressed audio data in a number of data formats. The media device may convert between the audio formats provided by the audio sources and the audio formats supported by audio playback devices. The media device may inspect frames of audio data to determine if the frames are to be decoded. The frame may be decoded and subsequently encoded into the data formats supported by the audio playback devices. To reduce latency, the media device may enable a pass-through mode to bypass the decoding of the frames to allow the frames to be decoded at the audio playback devices. A bi-directional loopback application may route audio data received over the ARC or eARC interface from the audio sources to the audio playback devices.