Compact plug-in noise cancellation device
A noise cancellation device (NCD) comprises a microphone, an analog-to-digital converter, a digital-to-analog converter, a rechargeable battery, and a processor. The NCD acquires an audio input, from an external device such as a stethoscope or a cell phone, and passes the analog data into an ADC (analog-to-digital converter) for signal conversion. The digitized signals are then passed to the processor for further processing. The processor contains all the processing functions such as preprocessing (divide the input data into frames and apply shaping function to each frame), short term Fourier transform (STFT), adaptive filtering, inverse STFT, and signal synthesis.
1. A noise cancellation device, wherein said noise cancellation device is a portable light weight and plug-in device suitable for real-time applications in a noisy environment based on actual needs, and comprising
a primary microphone;
a background microphone;
an analog-to-digital converter (ADC);
a signal enhancement processor;
a digital-to-analog converter (DAC); and
a rechargeable power supply; wherein
said signal enhancement processor further comprises two short-time Fourier transforms (STFTs), an adaptive filter and an Inverse STFT and said signal enhancement processor conducts a function of adaptive filtering with the background noise signal as the reference signal so as to filter out the noise signal contained in the mixed sound signal and obtain the enhanced signal of high signal-to-noise ratio (SNR);
wherein said noise cancellation device is used in a bi-directional communication comprising cell phone communications, two 4-pole sockets are provided in said noise cancellation device, one 4-pole socket is connected to a cell phone 4-pole headset for acquiring a microphone signal from the cell phone 4-pole headset and transmitting a stereo signal from a cell phone to the cell phone 4-pole headset, the other 4-pole socket is connected to the cell phone for transmitting a real-time enhanced speech signal to the cell phone and receiving the stereo signal from the cell phone, and there is a transmission path between the two 4-pole sockets for transmitting the stereo signal from the cell phone to the cell phone 4-pole headset.
2. The noise cancellation device of claim 1 , wherein said signal enhancement processor conducts said function of adaptive filtering in frequency domain with an algorithm of Minimal Mean Squared Error in Frequency domain with N-coefficient and Signal Detection (FMSENSD) comprising
an input comprising a mixed sound signal and a reference noise signal;
an output comprising a filtered sound;
parameters comprising a filter length;
an algorithm, comprising:
computing spectral magnitudes of mixed sound;
computing spectral magnitudes of reference noise;
estimating a channel response a first time using signal components in the mixed sound;
computing a residual a first time;
extracting silence regions;
estimating the channel response a second time using noise only signal components;
computing the residual a second time;
reconstructing time domain signals;
wherein said filter length is a design parameter which can be adjusted by a user based on reverberant conditions.