The results of experimental studies on application of selected simple machine learning (ML) methods for detection of atrial fibrillation (AFib) based on photoplethysmogram (PPG) are presented in the paper. The goal of the studies was to compare the performance of AFib detection using different ML algorithms in short PPG segments containing 32 consecutive cardiac cycles. Four parameters describing time series of interbeat intervals (IBI) were derived from the time domain Heart Rate Variability (HRV) and used as features for classification algorithms. Optimal values of metaparameters for all considered ML algorithms were experimentally determined. Accuracy, sensitivity, specificity and F1-score were then calculated to measure the quality of detection performance of each classification algorithm.
KEYWORDS: Microcontrollers, Fourier transforms, Signal processing, Digital signal processing, Interfaces, Analog electronics, Clocks, Statistical analysis, Intelligence systems, Oscilloscopes
In this paper, a real-time implementation of pitch shifting with use of phase vocoder algorithm is presented. The goal was to create a system that would allow to process audio signal in real time with use of a general purpose microcontroller. The task was a challenge due to relative complexity of the algorithm and limited computational capacity of the microcontroller, whose architecture is by nature much more universal than that of dedicated digital signal processors. The results of experiments with the developed system are presented and discussed in the paper.
KEYWORDS: Digital signal processing, Fourier transforms, Continuous wavelet transforms, Signal processing, Wavelets, Time-frequency analysis, Statistical analysis, Signal analyzers, Wavelet transforms
In this paper, we present the techniques used for modifying the spectral content (pitch shifting) and for changing the time duration (time scaling) of an audio signal. A short introduction gives a necessary background for understanding the discussed issues and contains explanations of the terms used in the paper. In subsequent sections we present three different techniques appropriate both for pitch shifting and for time scaling. These techniques use three different time-frequency representations of a signal, namely short-time Fourier transform (STFT), continuous wavelet transform (CWT) and constant-Q transform (CQT). The results of simulation studies devoted to comparison of the properties of these methods are presented and discussed in the paper.
KEYWORDS: Digital signal processing, Signal processing, Microcontrollers, Analog electronics, Real-time computing, Computer simulations, Reflection, MATLAB, Acoustics, Linear filtering
The paper is devoted to studies on possibilities of realization of guitar audio effects by means of methods of digital signal processing. As a result of research, some selected audio effects corresponding to the specifics of guitar sound were realized as the real-time system called Digital Guitar Multi-effect. Before implementation in the system, the selected effects were investigated using the dedicated application with a graphical user interface created in Matlab environment. In the second stage, the real-time system based on a microcontroller and an audio codec was designed and realized. The system is designed to perform audio effects on the output signal of an electric guitar.
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