librosa/core/spectrum.py
def amplitude_to_db(S, ref=1.0, amin=1e-5, top_db=80.0):
    '''Convert an amplitude spectrogram to dB-scaled spectrogram.

    This is equivalent to ``power_to_db(S**2)``, but is provided for convenience.

    Parameters
    ----------
    S : np.ndarray
        input amplitude

    ref : scalar or callable
        If scalar, the amplitude `abs(S)` is scaled relative to `ref`:
        `20 * log10(S / ref)`.
        Zeros in the output correspond to positions where `S == ref`.

        If callable, the reference value is computed as `ref(S)`.

    amin : float > 0 [scalar]
        minimum threshold for `S` and `ref`

    top_db : float >= 0 [scalar]
        threshold the output at `top_db` below the peak:
        ``max(20 * log10(S)) - top_db``


    Returns
    -------
    S_db : np.ndarray
        ``S`` measured in dB

    See Also
    --------
    power_to_db, db_to_amplitude

    Notes
    -----
    This function caches at level 30.
    '''

    S = np.asarray(S)

    if np.issubdtype(S.dtype, np.complexfloating):
        warnings.warn('amplitude_to_db was called on complex input so phase '
                      'information will be discarded. To suppress this warning, '
                      'call amplitude_to_db(np.abs(S)) instead.')

    magnitude = np.abs(S)

    if six.callable(ref):
        # User supplied a function to calculate reference power
        ref_value = ref(magnitude)
    else:
        ref_value = np.abs(ref)

    power = np.square(magnitude, out=magnitude)

    return power_to_db(power, ref=ref_value**2, amin=amin**2,
                       top_db=top_db)
def amplitude_to_db(S, ref=1.0, amin=1e-5, top_db=80.0):
    '''Convert an amplitude spectrogram to dB-scaled spectrogram.

    This is equivalent to ``power_to_db(S**2)``, but is provided for convenience.

    Parameters
    ----------
    S : np.ndarray
        input amplitude

    ref : scalar or callable
        If scalar, the amplitude `abs(S)` is scaled relative to `ref`:
        `20 * log10(S / ref)`.
        Zeros in the output correspond to positions where `S == ref`.

        If callable, the reference value is computed as `ref(S)`.

    amin : float > 0 [scalar]
        minimum threshold for `S` and `ref`

    top_db : float >= 0 [scalar]
        threshold the output at `top_db` below the peak:
        ``max(20 * log10(S)) - top_db``


    Returns
    -------
    S_db : np.ndarray
        ``S`` measured in dB

    See Also
    --------
    power_to_db, db_to_amplitude

    Notes
    -----
    This function caches at level 30.
    '''

    S = np.asarray(S)

    if np.issubdtype(S.dtype, np.complexfloating):
        warnings.warn('amplitude_to_db was called on complex input so phase '
                      'information will be discarded. To suppress this warning, '
                      'call amplitude_to_db(np.abs(S)) instead.')

    magnitude = np.abs(S)

    if six.callable(ref):
        # User supplied a function to calculate reference power
        ref_value = ref(magnitude)
    else:
        ref_value = np.abs(ref)

    power = np.square(magnitude, out=magnitude)

    return power_to_db(power, ref=ref_value**2, amin=amin**2,
                       top_db=top_db)
Convert an amplitude spectrogram to dB-scaled spectrogram.

    This is equivalent to ``power_to_db(S**2)``, but is provided for convenience.

    Parameters
    ----------
    S : np.ndarray
        input amplitude

    ref : scalar or callable
        If scalar, the amplitude `abs(S)` is scaled relative to `ref`:
        `20 * log10(S / ref)`.
        Zeros in the output correspond to positions where `S == ref`.

        If callable, the reference value is computed as `ref(S)`.

    amin : float > 0 [scalar]
        minimum threshold for `S` and `ref`

    top_db : float >= 0 [scalar]
        threshold the output at `top_db` below the peak:
        ``max(20 * log10(S)) - top_db``


    Returns
    -------
    S_db : np.ndarray
        ``S`` measured in dB

    See Also
    --------
    power_to_db, db_to_amplitude

    Notes
    -----
    This function caches at level 30.