Suno's default synth behavior is plucky and rhythmic — it wants to chop notes, not hold them. Long sustained leads need explicit sustain instructions, and v6 handles this noticeably better than v5.5.
1. Say 'sustained' and 'legato' explicitly:
bright synth lead, sustained long notes, legato, smooth release — 'legato' and 'sustained' are the two words that matter most. Without them you get plucks.
2. Ban the pluck: Exclude field: staccato, plucky, short notes, arpeggio. Suno's synth hand loves arpeggios; forbid them.
3. Reference the sound: Summertime-style bright lead synth, smooth and singing, like a synth whistle — the 'whistle' comparison pushes toward continuous tone.
4. Use v6 if you aren't. v5.5 truncates sustained synth notes much more aggressively. If you're on 5.5 and the lead keeps getting chopped, that's likely the whole problem — regenerate on v6.
5. Slow the part down. If the melody is dense with fast notes, Suno can't sustain any of them. Long notes need space — half notes and whole notes in your lyric/melody structure, not runs.
Good luck! Hank founder of SonorixPG