Single-Bit Audio Mapping for Constant Edge Rate Playback
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Solution Overview
Problem
Single-bit audio streams with data-dependent edge rates produce undesirable playback artifacts in current-steering digital analog converters, leading to poor total harmonic distortion and noise, and existing volume control methods affect audio quality.
Innovation Solution
Direct mapping is used to convert single-bit audio streams to a modified stream with a constant edge rate while maintaining the modulation index, employing a pre-filter bank and multi-bit symbol mapper to select symbols, and implementing two-stage volume control in digital and analog circuitry for improved volume control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a return-to-zero (RTZ) format with gap insertion is used to obtain constant edge rate, then edge rate becomes constant, but signal attenuation and noise increase
Solution Approach 1:
The patent extracts only the necessary edge rate control function from the RTZ format, removing the gap insertion component that causes signal attenuation and noise. The solution maintains constant edge rate by controlling transition timing without introducing unnecessary gaps between symbols.
Solution Approach 2:
The patent uses simple timing control logic instead of complex RTZ gap insertion mechanisms, achieving constant edge rate with minimal computational overhead and without the harmful side effects of gap-related attenuation and noise.
2Reliability
If gap is inserted between symbols to ensure transitions, then edge rate becomes constant, but modulation index changes and audio quality deteriorates
Solution Approach 1:
The patent removes the gap insertion mechanism entirely, achieving transition control through timing-based edge rate management that preserves the original modulation index and audio information without distortion.
Solution Approach 2:
The patent changes the control parameter from gap insertion (time-domain separation) to edge rate timing control (transition timing management), maintaining modulation index integrity while achieving constant edge rate.
3Ease of operation
If conventional modulator is used for volume control, then volume adjustment is achieved, but audio quality is affected
Solution Approach 1:
The patent replaces the conventional modulator-based volume control mechanism with direct digital gain adjustment in the PWM generation stage, eliminating the audio quality degradation associated with modulation-based volume control while maintaining ease of operation.
Data Source
AI summary
A single-bit audio stream can be converted to a modified single-bit audio stream with a constant edge rate while maintaining a modulation index of the original audio stream using direct mapping. With direct mapping, a pre-filter bank may be combined with a multi-bit symbol mapper to select symbols for the modified audio stream with a constant edge rate per symbol and the same modulation index as the original audio stream. The output of the pre-filter bank may be an audio stream with no consecutive full-scale symbols. Using the output of the pre-filter bank, a multi-bit symbol mapper may use the symbol selector to output a symbol with a constant edge rate per symbol and the same modulation index as the original signal. The symbols may be converted to an analog signal for reproduction of audio content using a transducer.