code: def damping(temp, relhum, freq, pres=101325):
      
      temp += 273.15  # convert to kelvin
      pres = pres / 101325.0  # convert to relative pressure
      c_humid = 4.6151 - 6.8346 * pow((273.15 / temp), 1.261)
      hum = relhum * pow(10.0, c_humid) * pres
      tempr = temp / 293.15  # convert to relative air temp (re 20 deg C)
      frO = pres * (24.0 + 4.04e4 * hum * (0.02 + hum) / (0.391 + hum))
      frN = (pres * pow(tempr, -0.5) * (9.0 + 280.0 * hum * math.exp(-4.17 *
          (pow(tempr, (-1.0 / 3.0)) - 1.0))))
      damp = (8.686 * freq * freq * (
              1.84e-11 * (1.0 / pres) * math.sqrt(tempr) +
              pow(tempr, -2.5) *
              (
                  0.01275 * (math.exp(-2239.1 / temp) * 1.0 /
                  (frO + freq * freq / frO)) +
                  0.1068 * (
                      math.exp(-3352 / temp) * 1.0 /
                      (frN + freq * freq / frN)
                  )
              )
          )
      )
      return damp
docs: Calculates the damping factor for sound in dB/m
      depending on temperature, humidity and sound frequency.
      Source: http://www.sengpielaudio.com/LuftdaempfungFormel.htm
  
      temp: Temperature in degrees celsius
      relhum: Relative humidity as percentage, e.g. 50
      freq: Sound frequency in herz
      pres: Atmospheric pressure in kilopascal