speech

signal

spectrogram: A spectrogram of a time signal is a special two-dimensional representation that displays time in its horizontal axis and frequency in its vertical axis.

short-time Fourier analysis

Why use it?
Some regions of speech signals shorter than 100 milliseconds often appear to be periodic, so that we can use the exact definition of Fourier
transform.

spectral leakage

This phenomenon is called spectral leakage because the amplitude of one harmonic leaks over the rest and masks its value.

feature extraction

Representation of speech signals in the frequency domain is especially useful because the frequency structure of a phoneme is generally unique.

Sinusoids are important because speech signals can be decomposed as sums of sinusoids.

For voiced sounds there is typically more energy at low frequencies
than at high frequencies, also called roll-off. To make the spectrograms easier to read, sometimes the signal is first preemphasized (typically with a first-order difference FIR filter) to boost the high frequencies
to counter the roll-off of natural speech.

Digital Systems

Linear Time-Invariant Systems and Linear Time-Varying Systems.

The Fourier Transform

Z-Transform

digital filter

filterbank

A filterbank is a collection of filters that span the whole frequency spectrum.

short-time analysis