What is a double flat?

A double flat is an accidental that lowers a pitch by two half-steps. In musical terms, each flat lowers a note by a half-step, so when you see a double flat, it indicates that the pitch should be lowered by a full step or two half-steps. This is often used to modify note values and create specific harmonic or melodic effects in a piece of music. It is particularly useful in certain keys or passages to ensure that the notes remain within the desired tonal framework or to adhere to certain theoretical principles.

The other options do not accurately reflect the function of a double flat. For example, an accidental that raises a pitch by one half-step refers to a sharp, while one that retains the note's original value would be interpreted as a natural sign. An accidental that sharpens a note without raising it drastically does not apply to the definition of double flats either. Thus, the correct understanding of a double flat is crucial for interpreting music correctly.