Glossary ======== .. 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 :term:`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 :term:`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 :term:`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.