peterf@2: Glossary
peterf@2: ========
peterf@2: 
peterf@2: .. glossary::
peterf@2: 
peterf@2:     time series
peterf@2:         Typically an audio signal, denoted by ``y``, and represented as a
peterf@2:         one-dimensional *numpy.ndarray* of floating-point values.  ``y[t]`` 
peterf@2:         corresponds to amplitude of the waveform at sample ``t``.
peterf@2:     
peterf@2:     sampling rate
peterf@2:         The (positive integer) number of samples per second of a time series.  
peterf@2:         This is denoted by an integer variable ``sr``.
peterf@2: 
peterf@2:     frame
peterf@2:         A short slice of a :term:`time series` used for analysis purposes.  This
peterf@2:         usually corresponds to a single column of a spectrogram matrix.
peterf@2: 
peterf@2:     window
peterf@2:         A vector or function used to weight samples within a frame when computing
peterf@2:         a spectrogram.
peterf@2: 
peterf@2:     frame length
peterf@2:         The (positive integer) number of samples in an analysis window (or
peterf@2:         :term:`frame`).
peterf@2:         This is denoted by an integer variable ``n_fft``.
peterf@2: 
peterf@2:     hop length
peterf@2:         The number of samples between successive frames, e.g., the columns
peterf@2:         of a spectrogram.  This is denoted as a positive integer ``hop_length``.
peterf@2: 
peterf@2:     window length
peterf@2:         The length (width) of the window function (e.g., Hann window).  Note that this
peterf@2:         can be smaller than the :term:`frame length` used in a short-time Fourier
peterf@2:         transform.  Typically denoted as a positive integer variable ``win_length``.
peterf@2: 
peterf@2:     spectrogram
peterf@2:         A matrix ``S`` where the rows index frequency bins, and the columns index
peterf@2:         frames (time).  Spectrograms can be either real-valued or complex-valued.  By
peterf@2:         convention, real-valued spectrograms are denoted as *numpy.ndarray*\ s ``S``,
peterf@2:         while complex-valued STFT matrices are denoted as ``D``.
peterf@2: 
peterf@2:     onset (strength) envelope
peterf@2:         An onset envelope ``onset_env[t]`` measures the strength of note onsets at
peterf@2:         frame ``t``.  Typically stored as a one-dimensional *numpy.ndarray* of
peterf@2:         floating-point values ``onset_envelope``.
peterf@2: 
peterf@2:     chroma
peterf@2:         Also known as pitch class profile (PCP).  Chroma representations measure the
peterf@2:         amount of relative energy in each pitch class (e.g., the 12 notes in the 
peterf@2:         chromatic scale) at a given frame/time.