# GlossaryΒΆ

- 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.