Optimization of temporal filters in the modulation frequency domain for constructing robust features in speech recognition

2007 ◽  
Author(s):  
Jeih-weih Hung
Keyword(s):  
Speech Recognition ◽  
Frequency Domain ◽  
Modulation Frequency

scholarly journals Photon Phase Shift Imaging Research on Frequency Domain Diffuse Optic Tomography

2021 ◽  
Author(s):  
huseyin ozgur kazanci
Keyword(s):  
Phase Shift ◽  
Frequency Domain ◽  
Laser Intensity ◽  
Model Problem ◽  
Modulation Frequency ◽  
Forward Model ◽  
Problem Solution ◽  
Inverse Problem Solution ◽  
Phase Data ◽  
Cartesian Coordinate

Abstract Diffuse optic imaging is an important biomedical optic research tool. Diffuse optic tomography (DOT) modality needs progressive philosophical approaches for scientific contribution. Technological developments and philosophical approaches should both go forward. Phase-shift based frequency domain (FD) diffuse optical tomography (FDDOT) method was well established in the literature. The instruments were tested for brain neurofunctional imaging. A mixture of AC laser intensity and phase data were used at these works. According to those works; deep volume resolution was improved by only using phase data. Because phase data is only related to the photon mean free path in imaging tissue media. Besides this advantage, laser intensity data is also affected by noisy background light and electrical artifacts. Another most important advantage of only using phase data can be explained as time-resolved temporal change can be directly related to phase shift of modulated frequency source. At this work, the frequency domain (FD) DOT imaging method which uses phase shift data were used for simulation phantom. Laser source-driven forward model problem weight matrix simulation data was given to the simple pseudo-inverse-based inverse problem solution algorithm for one inclusion example. The inclusion image was reconstructed and demonstrated successfully. Forward model problem weight functions inside the tissue simulation media were calculated and used based on the phase shifts at the same core modulation frequency. 100 MHz modulation frequency was selected due to its FDDOT standard. 13 sources and 13 detectors were placed on the back-reflected imaging surface. 40 x, y, z cartesian coordinate grid elements were used in the image reconstruction algorithm. Photon absorption coefficient: ma = 0.1 cm-1, and scattering coefficient: ms = 100 cm-1 values were set for background simulation phantom. One inclusion object was embedded inside the imaging tissue simulation phantom background. x, y, z cartesian coordinate grid sizes were selected for 100 mm for each direction. Photon phase shift fluencies were added to the forward model problem. The forward model problem was built according to the frequency domain photon migration diffusion approximation. Forward model problem photon fluencies were calculated according to the diffusion equation approximation. The simple pseudoinverse mathematical inverse problem solution algorithm was applied to test the results. The embedded inclusion object was reconstructed successfully with the high-resolution image quality. In general, DOT techniques suffer for the low image quality, but in this work, the high-quality image was reconstructed and demonstrated. The philosophical approach has future promising DOT imaging capability. The phase shift version of the FDDOT modality has an important advantage for future purpose.

scholarly journals Electro-acustic influence of the measuring system on the photoacoustic signal amplitude and phase in frequency domain

2016 ◽  
Vol 14 (1) ◽  
pp. 9-20 ◽  
Author(s):  
Sanja Aleksic ◽  
Dragana Markushev ◽  
Dragan Pantic ◽  
Mihajlo Rabasovic ◽  
Dragan Markushev ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Flicker Noise ◽  
Modulation Frequency ◽  
Signal Amplitude ◽  
Photoacoustic Signal ◽  
Measuring System ◽  
Coherent Noise ◽  
Characteristic Frequencies ◽  
Signal Distortions ◽  
Set Up

The paper discusses the most common impacts of the measuring system on the amplitude and phase of the photoacoustic signals in the frequency domain using the open-cell experimental set-up. The highest signal distortions are detected at the ends of the observed modulation frequency range from 20 Hz to 20 kHz. The attenuation of the signal is observed at lower frequencies, caused by the electronic filtering of the microphone and sound card, with characteristic frequencies of 15 Hz and 25 Hz. At higher frequencies, the dominant signal distortions are caused by the microphone acoustic filtering, having characteristic frequencies around 9 kHz and 15 kHz. It has been found that the microphone incoherent noise, the so called flicker noise, is negligibly small in comparison to the signal and does not affect the signal shape. However, a coherent noise originating from the power modulation system of the light source significantly affects the shape of the signal in the range greater than 10 kHz. The effects of the coherent noise and measuring system influence are eliminated completely using the relevant signal correction procedure targeting the photoacoustic signal generated by the sample.

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