Audio Clock Synchronization via Pseudorandom Correlation
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Solution Overview
Problem
Audio system impulse response measurements are degraded when playback and recording devices use unsynchronized clocks, leading to roll-off in measured frequency response at higher frequencies, especially when using external devices with less accurate timing references.
Innovation Solution
A system and algorithm that estimates the sample clock difference between playback and recording devices by playing a pseudorandom sequence, calculating the correlation lag, and resampling the recorded audio to synchronize the clocks, using a maximum length sequence or other pseudorandom sequences with sharp correlation peaks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If external recording devices with less accurate timing references are used, then wireless recording and room measurement flexibility is improved, but clock synchronization accuracy deteriorates causing frequency response roll-off
Solution Approach 1:
The patent changes the parameter of clock rate by measuring the actual clock rates of both playback and recording devices, then applying a resampling ratio calculated from these measured parameters to correct the frequency response measurements and eliminate roll-off effects
Solution Approach 2:
The patent replaces the need for precise mechanical clock synchronization with a software-based correction method that measures clock rate differences and compensates through digital resampling of the frequency response data
2Measurement precision
If synchronized clocks are used between playback and recording devices, then frequency response measurement accuracy is improved, but system complexity and clock synchronization requirements increase
Solution Approach 1:
The system performs self-measurement by having the recording device measure its own clock rate against the playback device's clock rate using the pseudorandom sequence, eliminating the need for external synchronization hardware or complex master-slave clock systems
Solution Approach 2:
The patent implements a feedback mechanism where the measured clock rate difference is used to calculate a correction factor (resampling ratio) that is then applied to the frequency response measurements to compensate for the timing mismatch
3Measurement precision
If pseudorandom sequences with sharp correlation peaks are used, then clock difference estimation accuracy is improved, but signal processing complexity increases
Solution Approach 1:
The patent uses periodic pseudorandom sequences (such as MLS sequences) that repeat at known intervals with sharp correlation peaks, allowing the system to measure clock differences by detecting the timing of these periodic correlation maxima across multiple sequence repetitions
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 method allows for accurate impulse response measurement and frequency response analysis by synchronizing clocks, preventing roll-off at higher frequencies and improving the adaptability of audio systems to specific room environments.
Implementation Method 1
calculating a lag at a correlation maximum utilizing multiple versions of the sequence
Implementation Method 2
resampling the recorded sequence and/or subsequent recorded audio, producing a resampled audio recording, to synchronize the clocks
Data Source
AI summary
Systems, methods, and algorithms for estimating the sample clock difference between an audio playback and recording device are described. The sample clock difference can be determined by sequentially playing the same pseudorandom signal and exploiting the statistical properties of said signal in the recording. An exemplary embodiment utilizes a maximum length sequence (MLS) for the pseudorandom signal. While an MLS sequence is a good choice for clock synchronization, it is possible to use other pseudorandom sequences. The sequence preferably has a sharp correlation peak that is clearly discernable with even a single sample shift and be of sufficient length to support the anticipated clock drift.