What is the most likely cause for a trumpet student's pitch to fall flat only at the ends of musical phrases?

When a trumpet student's pitch falls flat specifically at the ends of musical phrases, the most likely cause is a lack of breath support. Breath support is crucial for maintaining stable airflow and pressure when playing the trumpet, particularly during longer notes or phrases. As the player approaches the end of a phrase, they may be running low on air, leading to insufficient pressure to maintain the desired pitch. This can cause the notes to sag lower than intended, resulting in a flat sound.

Proper breath support allows for consistent airflow which is vital for maintaining pitch accuracy throughout a performance. This issue is often more pronounced at the end of phrases since the length and intensity of air used can diminish as the player completes the musical line. Encouraging students to focus on proper breathing techniques and to manage their air supply effectively can help mitigate this issue.

Other factors such as embouchure technique, fingerings, or mouthpiece choice may influence sound quality or comfort, but they are less likely to be the direct cause of pitch instability that specifically occurs at the end of phrases.