# Glossary

- time series
Typically an audio signal, denoted by

*y*, and represented as a one-dimensional*numpy.ndarray*of floating-point values.*y[t]*corresponds to amplitude of the waveform at sample*t*.- sampling rate
The (positive integer) number of samples per second of a time series. This is denoted by an integer variable

*sr*.- frame
A short slice of a time series used for analysis purposes. This usually corresponds to a single column of a spectrogram matrix.

- window
A vector or function used to weight samples within a frame when computing a spectrogram.

- frame length
The (positive integer) number of samples in an analysis window (or frame). This is denoted by an integer variable

*n_fft*.- hop length
The number of samples between successive frames, e.g., the columns of a spectrogram. This is denoted as a positive integer

*hop_length*.- window length
The length (width) of the window function (e.g., Hann window). Note that this can be smaller than the frame length used in a short-time Fourier transform. Typically denoted as a positive integer variable

*win_length*.- spectrogram
A matrix

*S*where the rows index frequency bins, and the columns index frames (time). Spectrograms can be either real-valued or complex-valued. By convention, real-valued spectrograms are denoted as*numpy.ndarray*s*S*, while complex-valued STFT matrices are denoted as*D*.- onset (strength) envelope
An onset envelope

*onset_env[t]*measures the strength of note onsets at frame*t*. Typically stored as a one-dimensional*numpy.ndarray*of floating-point values*onset_envelope*.- chroma
Also known as pitch class profile (PCP). Chroma representations measure the amount of relative energy in each pitch class (e.g., the 12 notes in the chromatic scale) at a given frame/time.