user: Question: What is the lowest Frequency where the Hemholtz pitch is d?
Columns: ['String', 'Scientific pitch', 'Helmholtz pitch', 'Interval from middle C', 'Frequency ( Hz )']
Types: ['text', 'text', 'text', 'text', 'real']
Sample row: ['1st', 'E 4', "e'", 'major third above', 329.63]
SQL:

assistant: SELECT MIN("Frequency ( Hz )") FROM "Table" WHERE "Helmholtz pitch" = 'd';