code: def _bss_source_crit(s_true, e_spat, e_interf, e_artif):
      
      # energy ratios
      s_filt = s_true + e_spat
      sdr = _safe_db(np.sum(s_filt**2), np.sum((e_interf + e_artif)**2))
      sir = _safe_db(np.sum(s_filt**2), np.sum(e_interf**2))
      sar = _safe_db(np.sum((s_filt + e_interf)**2), np.sum(e_artif**2))
      return (sdr, sir, sar)
docs: Measurement of the separation quality for a given source in terms of
      filtered true source, interference and artifacts.