Mobile Audio Volume Control Using Noise-Reference Dynamic Range Adjustment
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Solution Overview
Problem
Mobile communication devices face limitations in noise cancellation due to the close proximity of microphones, leading to incomplete noise reduction and speech signal distortion, especially in noisy environments, and existing volume control methods risk introducing clipping and distortion.
Innovation Solution
Implementing Multi-Microphone Active Noise Cancellation (MMANC) to generate a noise reference signal that controls Audio Dynamic Range Control (ADRC) and Automatic Volume Control (AVC), ensuring effective noise reduction and dynamic range compression without clipping, using a noise reference signal adjusted for stationary and non-stationary noise conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simple active noise filtering techniques are used, then device complexity is reduced, but noise cancellation performance deteriorates and speech signal distortion occurs
Solution Approach 1:
The patent divides the noise cancellation task into two distinct processing paths: a first adaptive filter processes the speech reference signal to generate a speech component, while a second adaptive filter processes the noise reference signal to generate a noise component. This segmentation allows each filter to be optimized for its specific function, improving overall performance without requiring excessive complexity in any single component.
Solution Approach 2:
The patent transitions from traditional single-microphone noise cancellation to a multi-dimensional approach using two microphones positioned at different locations. The speech reference microphone captures speech with minimal noise, while the noise reference microphone captures noise with minimal speech. This spatial dimensionality enables the system to separate and process speech and noise components independently, significantly improving noise cancellation effectiveness.
2Measurement precision
If the electrical signal is amplified to hear softer passages in noisy environments, then audio clarity for soft passages improves, but clipping and distortion occur in louder passages
Solution Approach 1:
The patent implements dynamic range control that continuously adapts the amplification factor based on the instantaneous amplitude of the audio signal. When the signal amplitude is low (softer passages), the system applies higher gain to enhance audibility. When the signal amplitude approaches maximum levels (louder passages), the system reduces gain to prevent clipping. This dynamic adjustment ensures optimal audio clarity across the entire dynamic range without introducing distortion.
Solution Approach 2:
The system employs feedback mechanisms where the output signal is monitored and used to adjust the amplification factor in real-time. The dynamic range control circuit continuously analyzes the signal levels and modifies the gain accordingly, creating a closed-loop system that prevents both under-amplification of soft passages and over-amplification of loud passages, thereby eliminating clipping and distortion while maintaining audio clarity.
3Volume of moving object
If microphones are placed close together in mobile devices, then device dimensions are reduced, but noise reference signal quality deteriorates
Solution Approach 1:
The patent assigns different functional roles to different microphone locations. The speech reference microphone is strategically positioned to capture speech signals with minimal noise contamination, while the noise reference microphone is positioned to capture noise signals with minimal speech contamination. This local optimization of microphone placement and function allows the system to maintain high signal quality despite the compact overall device dimensions.
Solution Approach 2:
The patent creates a dual-purpose microphone system where each microphone serves a specific primary function but both contribute to the overall noise cancellation process. The speech reference microphone primarily captures speech but its signal is also used in the adaptive filtering process to improve noise estimation. The noise reference microphone primarily captures noise but its signal contributes to enhancing speech detection. This multi-functionality maximizes the utility of each microphone component within the compact device.
Data Source
AI summary
A mobile audio device (for example, a cellular telephone, personal digital audio player, or MP3 player) performs Audio Dynamic Range Control (ADRC) and Automatic Volume Control (AVC) to increase the volume of sound emitted from a speaker of the mobile audio device so that faint passages of the audio will be more audible. This amplification of faint passages occurs without overly amplifying other louder passages, and without substantial distortion due to clipping. Multi-Microphone Active Noise Cancellation (MMANC) functionality is, for example, used to remove background noise from audio information picked up on microphones of the mobile audio device. The noise-canceled audio may then be communicated from the device. The MMANC functionality generates a noise reference signal as an intermediate signal. The intermediate signal is conditioned and then used as a reference by the AVC process. The gain applied during the AVC process is a function of the noise reference signal.