Hearing Amplifier Gain Control for Predictable Log Compression
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Solution Overview
Problem
Hearing amplification systems face challenges in providing a predictable, accurate, and controllable logarithmic compression over a wide dynamic range, leading to distortion issues due to unpredictable time constants in audio signal processing.
Innovation Solution
A variable gain amplifier system with a gain control circuit that includes a gain measurement circuit and a control signal generator, utilizing logarithmic converters and attenuators to adjust the gain dynamically, ensuring accurate and programmable compression, and controlling the time constant for optimal audio signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional electronics are used to operate over a wide dynamic range, then the system can cover the full operating range, but the electronics must possess high complexity and accuracy which increases cost
Solution Approach 1:
The patent introduces an optical intermediary (light source, optical modulator, photodetector) between the electrical input signal and the output signal. The input electrical signal modulates the light source optically, the light travels through an optical path, and is converted back to electrical signal by the photodetector. This optical intermediary enables wide dynamic range operation while keeping the electrical electronics relatively simple, as the optical domain naturally handles large signal ranges.
Solution Approach 2:
The patent replaces traditional electrical/electronic signal processing with an optical system. Instead of using complex electronic circuits to handle wide dynamic ranges, the system converts electrical signals to optical signals, processes them in the optical domain, and converts back to electrical. This substitution of mechanical/electrical system with optical system achieves the desired dynamic range with simpler electronics.
2Measurement precision
If analog logarithmic compression is implemented, then the compression transfer function can be highly predictable and accurate, but the time constant control becomes difficult leading to distortion
Solution Approach 1:
The patent makes the time constant dynamic and adjustable through electronic control. The optical system includes controllable components (optical modulator, light source intensity control) that can dynamically adjust the effective time constant of the logarithmic compression. This allows the system to maintain accurate compression transfer function while enabling flexible time constant control to prevent distortion, adapting to different operating conditions.
Solution Approach 2:
The patent enables changing of key parameters (gain, time constant, compression ratio) through electronic control of the optical system. By adjusting electrical control signals to the optical modulator and light source, the system can dynamically change operational parameters while maintaining the logarithmic compression characteristic. This provides both accuracy in compression and ease of time constant adjustment.
3Speed
If the time constant is made fast or slow to increase compression speed, then compression response improves, but audio signal distortion occurs
Solution Approach 1:
The patent implements feedback control in the optical system to optimize the time constant dynamically. The system monitors the compression process and adjusts the optical modulator and light source parameters in real-time to maintain optimal time constant values. This feedback mechanism ensures fast compression response when needed while preventing distortion by adjusting the time constant to appropriate values based on the input signal characteristics.
Data Source
AI summary
Embodiments of the invention provide an amplifier including a gain control circuit having a gain measurement circuit as part of a feedback loop. The gain measurement circuit generates an attenuated output signal, based on the gain of the amplifier circuit, which is used to generate a gain control signal. One amplifier includes a first attenuator enabling primary compression and a second attenuator as part of a gain measurement circuit. In some cases the attenuation factors of the first and second attenuators may be proportional or substantially the same. In some embodiments one or more output stages (e.g., differential amplifiers) are provided to generate the gain control signal based on differential combinations of an audio output, the attenuated output signal, and a primary threshold signal. A ratio of the gains of the two or more comparing amplifiers can set a primary compression ratio in some cases.