The Star-Spangled Banner spans an octave and a fifth (19 semitones). If a vocalist chooses an unsuitable key, the lowest notes ("say can you see") become an inaudible sub-harmonic murmur, or the high note on "free" forces an uncontrolled vocal break. Josh Levi's F Major transposition places the highest note at F4—an energetic, resonant belt for male contemporary R&B tenors.
Sound travels at 343 m/s (~1,125 ft/s). At Tottenham Hotspur Stadium or Wembley, the sound from center stage reaches the top upper tier and bounces back after 300 to 450 ms. When vocalists sing without custom isolated In-Ear Monitors (IEMs), the acoustic delay causes psychological speech-jamming, causing tempo dragging or missed pitches.
Royal Air Force or USAF flyovers over open-roof stadiums require exact 1-second tolerances. Because anthems are sung rubato (expressively varying tempo), the military air boss maintains live radio contact with the NFL ceremony stage manager, pacing the final approach turn based on the vocalist's benchmark timing at the second verse break.