With efficient tools for computing the Fourier transform in hand, in this lecture we briefly describe issues that arise when we try to use this tool to analyze signals. We will discuss two major issues. The first is the effect of only collecting a finite number of samples x[0], . . . , x[L − 1], rather than observing x[n] for all n. The second is what happens when the signal of interest has fre...

In this paper we present an example of the use of the singing voice as a controller for digital music synthesis. The analysis of the voice with spectral processing techniques, derived from the Short-Time Fourier Transform, provides ways of determining a performer’s vocal intentions. We demonstrate a prototype, in which the extracted vocal features drive the synthesis of a plucked bass guitar. T...

The Short Time Fourier Transform (STFT) and the Continuous Wavelet Transform (CWT) of accelerometer signals measured in patients with epilepsy are analyzed. Characteristics of the spectrogram and scalogram are studied in order to get more insight in how these transforms might be useful to derive suitable features for myoclonic seizure detection. First some artificial elementary patterns that re...

The presence of noise in a nonstationary signal (i.e., whose frequency content varies with time) complicates the extraction of meaningful information from the signal. The classical Fourier domain of such a signal can only separate the noise from the useful signal energy if they have different frequency content. For nonstationary signals the windowed Fourier transform has been introduced to loca...

A new approach has been proposed to reduce the computations involved in the ISAR imaging, which uses Harmonic Wavelet (HW) based Time-Frequency Representation (TFR). Since the HW based TFR falls into a category of non-parametric Time-Frequency (T-F) analysis tool, it is computationally efficient compared to parametric T-F analysis tools such as Adaptive Joint Time-Frequency Transform (AJTFT), A...

Short-time Fourier transform (STFT) methods are often used to overcome the degradation of speech signals affected by noise. STFT-gain functions are usually expressed as a function of the a priori SNR, say ξ, and good techniques to estimate ξ are of vital importance for the quality of enhanced speech. Often, ξ is estimated using the so-called decision directed approach (DD). However, the DD appr...

The subject matter presented in this paper deals with application of the short time Fourier transform (STFT) in processing the acoustic emission (AE) pulses generated by six basic forms of partial discharges (PDs) that can occur in insulation systems of power appliances. The paper presents the time-frequency analysis results of the AE pulses generated by the following spark gaps modeling the fo...

Mountain papaya fruits (Vasconcella pubescens) were tested for firmness with a nondestructive acoustic method for 14 days after harvest. The response of each fruit was analyzed with the Fourier transform to obtain a firmness index (FI) based on the second resonant frequency and with the Short Time Fourier Transform (STFT) to obtain a spectrogram frequency centroid (FC) index. The indexes were p...

The work undertaken in this research focuses on advanced condition monitoring and fault detection methods for wind turbines (WTs). Fourier Transform (FFT) and Short Time Fourier transform (STFT) algorithms are proposed to effectively extract fault signatures in generator current signals (GCS) for WT fault diagnosis. With this aim, a WT model has been implemented in the MATLAB/Simulink environme...