The behavior of a sound wave is affected by the density of the medium, the temperature of the medium and the pressure of the medium if it is a gas. Motion of the medium independent of the sound wave may also affect the way sound propagates.
Yes, you may check-in for your Delta Air Lines (DL) flight with your mobile device starting 24 hours and ending 60 minutes before the scheduled departure time (depending on your departure city and destination) to receive a mobile boarding pass on your mobile device.
Passengers should check-in at least three hours before the flight is due to take off. Check-in counters close one hour prior to departure. Air Transat also offers passengers the opportunity to check in online 24 hours prior to the departure of their flight depending on the departure airport.