Network Audio Synchronization Using Common Reference Clock
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Solution Overview
Problem
Current methods for synchronizing audio playback in multi-room audio systems face challenges such as high latency and unsynchronized playback due to differing prebuffer sizes and crystal tolerances, and existing protocols like RTP are inadequate for high-fidelity audio, especially in heterogeneous networks.
Innovation Solution
A method that uses a common reference clock, provided by a wall clock server, to synchronize audio playback devices across a network, allowing for simultaneous start-up and synchronized playback by adjusting local clocks and compensating for network jitter, independent of hardware-dependent time information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If remote control signals are used to start playback stations, then playback can be initiated across multiple devices, but signal offset of 200-500 msec occurs leading to unsynchronized playback
Solution Approach 1:
The system performs preliminary actions by pre-filling buffers with audio data before actual playback begins. The transport controller calculates required prebuffer sizes and triggers data transmission in advance, ensuring all devices are ready to start simultaneously without waiting for remote control signals to propagate across the network.
Solution Approach 2:
The system implements feedback mechanisms where the transport controller continuously monitors playback status, buffer levels, and synchronization states of all audio adapters. Based on this feedback, the controller dynamically adjusts prebuffer sizes and transmission timing to maintain synchronized playback across all devices.
2Productivity
If different prebuffer sizes are used for different audio formats, then playback can be optimized for each format, but synchronization between devices is compromised
Solution Approach 1:
The system dynamically changes the prebuffer size parameter based on the audio format being played. The transport controller identifies the audio format and calculates the appropriate prebuffer size for that specific format, then configures all audio adapters with matching prebuffer sizes. This ensures both format optimization and synchronization across devices.
3Device complexity
If crystal tolerances of converter chips are not compensated, then device complexity is reduced, but phase drift occurs over time leading to unsynchronized playback
Solution Approach 1:
The system implements a feedback-based synchronization mechanism where the transport controller continuously monitors the playback phase of each audio adapter and compares it against a reference. When phase deviations are detected, the controller sends correction signals to adjust the playback timing of affected devices, compensating for crystal tolerance variations without requiring complex hardware modifications.
4Speed
If RTP protocol is used for transmission, then real-time transport capability is improved, but packet loss occurs in wireless networks leading to audible dropouts
Solution Approach 1:
The system applies beforehand cushioning by calculating and applying additional time margins and error correction codes before data transmission. The transport controller determines the required cushioning time based on network conditions and audio format, then prepends this buffer to the data stream. This ensures that even if packets are lost or delayed during wireless transmission, the audio playback remains continuous without audible dropouts.
Data Source
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AI summary
The invention relates to a method and arrangement for synchronising data streams in networks and to a corresponding computer program and corresponding computer-readable storage medium which can be used, in particular, for synchronising different audio playback devices (audio adapters) within a home network. Said home network can be a conventional computer network comprising both wireline and wireless components. According to the invention, in order to synchronise the data output in networks in which at least one data stream is transmitted by a network unit to at least two output units of the network, where said stream is outputted, first common time information is made available to at least the output units and the output of the data in the data stream is synchronised at least in terms of the phase and/or frequency on the basis of the first common time information.