Wireless Microphone Clock Synchronization via Phase Feedback
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Solution Overview
Problem
Wireless digital audio systems face challenges in synchronizing audio sampling times across devices due to the absence of a delay-free connection, leading to phase noise and the need for sample rate conversion, which degrades audio quality and localization in multi-channel systems.
Innovation Solution
A wireless microphone and in-ear monitoring system with a clock master and slave configuration, utilizing a digital wireless transmission path for synchronization signals and audio, where the clock master provides a sample clock and synchronization interface, allowing the slave device to adjust its sample clock using a phase-locked loop to match the master clock, ensuring frequency and phase synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If wireless digital transmission is used for audio signals, then wireless freedom and flexibility are improved, but synchronization precision deteriorates due to the absence of a delay-free connection
Solution Approach 1:
The patent introduces a timing reference signal as an intermediary carrier that travels through the wireless transmission path along with the audio data. This reference signal serves as a mediator that allows the receiving device to measure and compensate for transmission delays, thereby maintaining synchronization precision while enjoying wireless freedom.
Solution Approach 2:
The patent implements a feedback mechanism where the receiving device measures the arrival time of the timing reference signal, calculates the synchronization offset, and adjusts its audio processing accordingly. This closed-loop feedback ensures that synchronization precision is maintained despite the wireless transmission path.
2Adaptability or versatility
If independent clock generators are used in each device, then device independence and flexibility are improved, but phase alignment deteriorates due to clock tolerances and temperature differences
Solution Approach 1:
The patent uses the timing reference signal to create a feedback loop that allows each device to independently adjust its clock based on the actual arrival time of the reference signal. This enables devices to maintain phase alignment while keeping their independent clock generators, combining device independence with precise synchronization.
Solution Approach 2:
The patent allows devices to dynamically change their sampling clock parameters based on the measured timing offset from the reference signal. By adjusting the clock frequency or phase in response to measured conditions, the system maintains phase alignment despite variations in independent clock generators.
3Adaptability or versatility
If sample rate conversion is performed to handle clock deviations, then adaptability to different clock rates is improved, but audio quality deteriorates due to phase noise and conversion artifacts
Solution Approach 1:
The patent performs preliminary synchronization by embedding the timing reference signal in the transmitted audio stream before conversion. The receiving device uses this pre-provided reference to adjust its sampling clock in advance, avoiding the need for sample rate conversion and its associated quality degradation.
Solution Approach 2:
The patent converts the potential harm of clock rate variations into a beneficial synchronization mechanism. By intentionally including the timing reference signal that reveals the actual timing relationship, the system transforms what could be a source of synchronization errors into a tool for precise clock alignment, eliminating the need for quality-degrading sample rate conversion.
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
This solution enables precise synchronization of audio sampling times in wireless systems, improving audio quality and localization in stereo and surround sound applications by eliminating the need for sample rate conversion and maintaining accurate phase alignment.
Implementation Method 1
The clock master has a first timer. A first phase of the first clock signal is detected after the first timer has expired and the first phase is transmitted wirelessly to the at least one clock slave.
Data Source
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AI summary
A wireless microphone and/or in-ear monitor system is proposed that has at least one clock master (TM) for prescribing a word clock and at least one clock slave (TS) that can be synchronised to the word clock prescribed by the clock master (TM). Between the clock master (TM) and the at least one clock slave (TS) there is a digital wireless transmission link that digitally transmits both synchronisation signals and audio signals. The clock master (TM) has a clock reference in order to prescribe a first sample clock (S1). The clock master further has a synchronisation interface (SY) for wirelessly transmitting a synchronisation word (S). The clock master (TM) has a first timer (T1). A first phase (P1) of the first clock signal (S1) is detected after expiry of the first timer (T1) and the first phase (P1) is wirelessly transmitted to the at least one clock slave (TS). The at least one first clock slave (TS) has a second timer (T2). After expiry of the second timer (T2), a second phase (P2) of the second clock signal (S2) of the clock slave (TS) is detected and is compared with the wirelessly transmitted first phase (P1). The difference between the first and second phases (P1, P2) is used as an input variable for a control unit (R) in the at least one clock slave (TS). The control unit (R) adjusts an adjustable sample clock of the at least one clock slave (TS) such that it corresponds to the first clock (S1) of the clock master (TM).