If i were bungee jumping from a bridge while blowing a hand-held air horn and someone who remains on the bridge will hear a decreased pitch or frequency as the source is moving away from the stationary listener as per the Dooplers effect. Hence, the pitch will progressively lower as the source is moving away from the observer.
The pressure law states that for a constant volume of gas in a sealed container the temperature of the gas is directly proportional to its pressure. This can be easily understood by visualising the particles of gas in the container moving with a greater energy when the temperature is increased.