NICAM Audio Resampling With Non-Linear Clock Synchronization
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Solution Overview
Problem
The lack of synchronization between remote and local sample clocks in NICAM audio decoders leads to distortion and increased complexity and cost due to the need for extensive computations to correct these errors.
Innovation Solution
A digital sample rate converter with a digital up sampler, non-linear interpolator, phase differential calculator, and synchronizer is used to synchronize and interpolate digital samples, allowing for efficient conversion between different sample frequencies, including NICAM audio signals sampled at 32 kHz and local sample clocks at frequencies like 31.25 kHz, 44.1 kHz, or 48 kHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large number of computations are performed to eliminate distortion caused by clock desynchronization, then audio quality is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values in lookup tables before runtime. The resampler uses pre-computed phase correction data that is stored in memory, allowing the decoder to apply corrections with simple table lookups rather than performing complex real-time computations, thus maintaining audio quality while reducing device complexity
Solution Approach 2:
The patent uses copying by creating a digital model of the resampling process through lookup tables that store pre-computed correction data. Instead of implementing the full computational resampling algorithm in hardware, the system copies the essential correction information into tabular form that can be quickly accessed and applied, significantly reducing the computational burden on the decoder
2Reliability
If real-time resampling computations are performed to handle clock frequency differences, then synchronization is improved, but processing time increases
Solution Approach 1:
The patent performs resampling computations in advance and stores the results in lookup tables. During real-time operation, the system simply retrieves pre-computed values from memory based on the current phase difference, eliminating the need for time-consuming real-time calculations while maintaining accurate synchronization
Solution Approach 2:
The patent uses inexpensive memory structures (lookup tables) to store pre-computed resampling data. These tables are loaded once and then rapidly accessed during operation, replacing the need for expensive and time-consuming real-time computational resources while achieving the same synchronization accuracy
Data Source
AI summary
A NICAM audio signal re-sampler may include a non-linear interpolator configured to interpolate in a non-linear manner between sequential digital samples that are based on a stream of demodulated NICAM audio samples. A phase differential calculator may be included that compares phase information at different resolutions.