[dbfft] Power Spectrum in dB #python #dsp

dbfft.py

def dbfft(x, fs, win=None, ref=32768):
    """
    Calculate spectrum in dB scale
    Args:
        x: input signal
        fs: sampling frequency
        win: vector containing window samples (same length as x).
             If not provided, then rectangular window is used by default.
        ref: reference value used for dBFS scale. 32768 for int16 and 1 for float

    Returns:
        freq: frequency vector
        s_db: spectrum in dB scale
    """
    N = len(x)  # Length of input sequence
    if win is None:
        win = np.ones(1, N)
    if len(x) != len(win):
            raise ValueError('Signal and window must be of the same length')
    x = x * win
    # Calculate real FFT and frequency vector
    sp = np.fft.rfft(x)
    freq = np.arange((N / 2) + 1) / (float(N) / fs)

    # Scale the magnitude of FFT by window and factor of 2,
    # because we are using half of FFT spectrum.
    s_mag = np.abs(sp) * 2 / np.sum(win)

    # Convert to dBFS
    s_dbfs = 20 * np.log10(s_mag/ref)
    
    if len(freq) > len(s_dbfs):
        freq = freq[:len(s_dbfs)]
    if len(s_dbfs) > len(freq):
        s_dbfs = s_dbfs[:len(freq)]
        
    return freq, s_dbfs