FFT Shifting Audio Multiplexing for Single Channel Transmission
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Solution Overview
Problem
Sound isolating earphones and headsets typically receive only a single 'mono' audio channel from mobile devices, limiting the ability to process multiple microphone signals, such as ambient and ear canal microphone signals, which are essential for noise reduction and voice communication in noisy environments.
Innovation Solution
A method and system for multiplexing two or more audio signals into a single composite signal using frequency division multiplexing based on Fast Fourier Transform (FFT) shifting, allowing the composite signal to be transmitted over a standard audio input connection, such as TRRS, and then de-multiplexed back into original form for processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If frequency division multiplexing based on FFT shifting is used to transmit multiple audio channels over a single connection, then the quantity of audio signals transmitted is improved, but the device complexity increases
Solution Approach 1:
The patent segments multiple audio channels into different frequency bands using FFT shifting. Each audio channel is shifted to a unique frequency range (e.g., channel 1 to 0-8kHz, channel 2 to 8-16kHz) allowing simultaneous transmission over a single connection. The receiving device then segments these frequency bands back into individual channels for processing.
Solution Approach 2:
The patent changes the frequency parameter of audio signals through FFT shifting to enable multiplexing. By transforming audio channels from the time domain to the frequency domain and shifting their spectral content to different frequency ranges, multiple channels can coexist on a single transmission medium without interference.
2Measurement precision
If spectral expansion techniques are used to expand audio bandwidth, then the quality of audio signals is improved, but the processing complexity increases
Solution Approach 1:
The patent applies spectral expansion by operating in the frequency domain (another dimension) rather than just the time domain. FFT shifting transforms audio signals into the frequency domain where spectral manipulation can be performed to expand bandwidth and improve audio quality before converting back to time domain for playback.
Data Source
AI summary
A method and system for multiplexing audio signals into a single channel uses frequency division multiplexing. The frequency division multiplexing method herein is based on a frequency transform algorithm using FFT shifting that does not require a carrier signal for the modulation. In one embodiment, two input microphone audio signals are frequency shifted and the resulting single audio channel is directed over a standard input connection to a computing device, for instance, a smart phone using a wired TRRS connection. The TRRS analog input of the computing devices exhibits a high-pass characteristic, and the frequency shifting method enables the low frequency audio components of input audio signals to be received and processed by a software application on the smart phone. Other embodiments are disclosed.