Amplitude Modulated Optical Pickup for Stringed Instruments
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Solution Overview
Problem
Prior art optical pickups for musical instruments are susceptible to background light and electromagnetic interference, which causes unwanted noise due to the inability to effectively filter out background light noise that is indistinguishable from the desired audio signal.
Innovation Solution
An amplitude modulated optical pickup system using a vibrating element like a string to modulate the amplitude of an optical signal, which is then demodulated to produce a noise-free electrical signal, employing multiple photodetectors and distinct carrier frequencies to reduce noise and crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct frequency translation is used from string vibration to electrical output signal, then the system structure is simple, but background light noise is indistinguishable from the desired audio signal causing unwanted noise
Solution Approach 1:
The patent modulates the optical source at a high-frequency carrier (e.g., 1 MHz) that is well above the audio band, thereby separating the desired signal from background light noise in the frequency domain. This parameter change in modulation frequency allows subsequent filtering to eliminate noise while preserving the audio signal
Solution Approach 2:
The patent replaces direct mechanical vibration detection with an amplitude-modulated optical detection system. By using an optical source modulated at a carrier frequency and detecting amplitude variations, the system substitutes a more sophisticated detection mechanism that provides frequency separation capability, eliminating the noise problem of direct translation
2Object-affected harmful factors
If amplitude modulation with carrier frequency is used to modulate the optical source, then background light noise is effectively filtered out, but the device complexity increases due to additional modulation and demodulation circuitry
Solution Approach 1:
The patent employs periodic amplitude modulation of the optical source at a high-frequency carrier wave. This periodic action creates distinct frequency components that can be easily separated from continuous background noise through filtering, achieving noise rejection while using well-established modulation techniques
Solution Approach 2:
The patent introduces a high-frequency carrier signal as an intermediary between the optical source and the audio signal. This carrier acts as a mediator that carries the audio information in its amplitude variations, allowing the system to bypass the problem of direct audio-frequency optical detection that is susceptible to noise
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively eliminates or greatly reduces unwanted background noise, providing a clean electrical signal representative of the string vibration frequency and amplitude, improving sound reproduction quality.
Implementation Method 1
a first photodetector is in transmissive or reflective optical communication with the first optical source... an amplitude modulated (AM) photodetector signal output is thus generated from the first photodetector
Implementation Method 2
A vibrating element such as a string on a musical instrument is disposed in an optical path between the first optical source and the first photodetector whereby a vibration of the element varies and modulates an amplitude of the first output signal
Data Source
AI summary
A device and method for an amplitude modulated optical pickup for a stringed instrument are disclosed. A first optical source comprising a first output signal comprising a first carrier frequency is provided and a first photodetector is in optical communication with the first optical source. A vibrating element such as a string on a musical instrument is disposed in an optical path between the first optical source and the first photodetector whereby a vibration of the element varies and modulates an amplitude of the first output signal received by the photodetector that is proportional to an element vibration amplitude and is at the same frequency as the element vibration frequency. An amplitude modulated (AM) photodetector signal output is generated from the first photodetector. The resultant signal is then demodulated with appropriate circuitry to produce a substantially noise free electronic signal representative of the element vibration frequency.