Mast, Fog Horn, Funnel Port, and Funnel Starboard whistles sounded in sequence, followed by the Mast, Fog Horn, and Funnel Starboard whistles together at noon on a September 2014 transatlantic crossing.

Funnel whistle select on QM2 bridge

From the May 2024 Tech Spec :

Wikipedia (May 2024) says:

Ships signal to each other and to the shore with air horns, sometimes called whistles, that are driven with compressed air or from steam tapped from the power plant. Low frequencies are used, because they travel further than high frequencies; horns from ships have been heard as far as fifteen kilometres (ten miles). Traditionally, the lower the frequency, the larger the ship. The RMS Queen Mary, an ocean liner launched in 1934, had three horns based on 55 Hz (corresponding to A1 ), a frequency chosen because it was low enough that the very loud sound of it would not be painful to the passengers. Modern International Maritime Organization regulations specify that ships' horn frequencies be in the range 70–200 Hz (corresponding to C♯2-G3) for vessels that are over 200 m (660 ft) in length. For vessels between 200 and 75 m (660 and 250 ft) the range is 130–350 Hz and for vessels under 75 m (250 ft) it is 70–700 Hz.