NICAM Output Resampling for Clock Synchronization Without Distortion
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Solution Overview
Problem
The lack of synchronization between remote and local sample clocks in NICAM audio decoding leads to distortion and increased computational complexity, requiring costly and complex decoders to correct.
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 rates and frequencies, including NICAM audio signals.
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 decoder cost and complexity increase
Solution Approach 1:
The patent applies preliminary action by performing sample rate conversion at the output stage rather than requiring complex real-time synchronization during decoding. The digital sample rate converter resamples the decoded audio from 32 kHz to match the local sample clock frequency, eliminating distortion without requiring complex computations during the main decoding process. This approach maintains audio quality while avoiding the need for expensive, complex decoders.
Solution Approach 2:
The patent changes the sampling frequency parameter from the fixed 32 kHz NICAM standard to a variable frequency that matches the local sample clock. The digital sample rate converter dynamically adjusts the output sample rate based on the local clock frequency, allowing the system to handle clock desynchronization by changing the frequency parameter rather than through complex computational correction.
2Reliability
If real-time synchronization is implemented to prevent distortion, then audio quality is improved, but computational complexity increases
Solution Approach 1:
The patent performs sample rate conversion as a preliminary step after decoding but before digital-to-analog conversion. This preliminary action allows the system to prepare the audio data for the specific local sample clock frequency in advance, avoiding the need for complex real-time synchronization computations during critical audio processing stages.
Solution Approach 2:
The digital sample rate converter acts as an intermediary component between the fixed 32 kHz NICAM decoder output and the variable frequency local sample clock. This intermediary performs the frequency adaptation function, isolating the main decoder from synchronization complexity while ensuring audio quality matches the local clock requirements.
3Adaptability or versatility
If sample rate conversion is performed to match local clock frequency, then compatibility is improved, but processing time increases
Solution Approach 1:
The patent segments the audio processing into distinct stages: decoding at fixed 32 kHz, then separate sample rate conversion to match local clock frequency. This segmentation allows each stage to be optimized independently - the decoder operates at its native fixed rate without overhead, while the sample rate conversion handles frequency adaptation efficiently as a dedicated post-processing step.
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.