Single-Bit Audio Volume Control With Constant Edge-Rate Mapping
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Solution Overview
Problem
Single-bit audio streams with data-dependent edge rates produce undesirable playback artifacts and limited volume control in current audio devices, leading to poor harmonic distortion and noise in audio reproduction.
Innovation Solution
Direct mapping is employed to convert single-bit audio streams to a modified stream with a constant edge rate while maintaining the modulation index, using 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 audio quality and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a return-to-zero (RTZ) format is used to obtain a constant edge rate audio stream, then the edge rate becomes constant, but the analog output is attenuated and noise is introduced
Solution Approach 1:
The patent segments the single-bit audio stream into multi-bit symbols (e.g., 4-bit symbols) that can be independently selected from a pre-filter bank. This segmentation allows the system to choose symbols with specific edge rate characteristics without needing to modify every bit, thereby avoiding the attenuation and noise problems of RTZ while still achieving constant edge rates.
Solution Approach 2:
The patent changes the parameter representation from single-bit samples to multi-bit symbols. By mapping single-bit audio stream values to multi-bit symbols (e.g., mapping a '1' to symbols like '1100' or '0011' with controlled edge rates), the system achieves constant edge rates without the signal attenuation and noise introduction that occur with RTZ formatting.
2Stability of the object's composition
If gaps are inserted between symbols in RTZ format to obtain transitions, then edge rate becomes constant, but the modulation index changes and signal is attenuated
Solution Approach 1:
The patent employs dynamic symbol selection from a pre-filter bank, where the system adaptively chooses multi-bit symbols based on the desired edge rate characteristics. This dynamic approach allows the system to maintain the modulation index by selecting appropriate symbols without inserting gaps, thereby preserving signal strength and avoiding information loss.
Solution Approach 2:
The patent introduces a pre-filter bank containing multiple multi-bit symbols as an intermediary between the single-bit audio stream and the output. This pre-filter bank acts as a mediator that provides pre-computed symbols with controlled edge rates, eliminating the need for gap insertion and the associated signal attenuation and modulation index changes.
3Ease of operation
If conventional modulators are used for volume control on digital signals, then volume control is achieved, but the quality of reproduced audio is affected
Solution Approach 1:
The patent applies preliminary volume control by selecting multi-bit symbols with appropriate edge rates and amplitude characteristics from the pre-filter bank before the audio signal is converted to analog form. This preliminary action allows volume adjustment without using conventional modulators, thereby maintaining audio quality while achieving the desired volume level.
Data Source
AI summary
Audio content in a single-bit audio stream can be reproduced at a transducer by mapping the single-bit audio stream to symbols in a multi-bit audio stream. Volume control may be implemented, in part, in the digital domain and, in part, in the analog domain. In the digital domain, when converting the single-bit audio stream to a plurality of symbols, the plurality of symbols is selected based, at least in part, on audio content of the single-bit audio stream and a desired volume level. In the analog domain, when converting an analog current signal output from a current-steering DAC processing the plurality of symbols to an analog voltage signal, an analog gain value may be selected based, at least in part, on the desired volume level.