which is often considered as the threshold of human hearing (roughly the sound of a mosquito flying 3 m away). The proper notations for sound pressure level using this reference are L p /(20 μPa) or L p (re 20 μPa), but the suffix notations dB SPL, dB(SPL), dBSPL, or dB SPL are very common, even if they are not accepted by the SI.