Key signature A minor as each accidental may be notated explicitly as required, or the piece may be modal or atonal. An example is Bartók's Piano Sonata, which has no fixed key and is highly chromatic. If not bound by common practice conventions, microtones can also be notated in a key signature; which microtonal symbols are used depends on the system. The common practice period conventions are so firmly established that some musical notation programs have been unable to show nonstandard key signatures until recently. The use of a one-flat signature developed in the Medieval period, but signatures with more than one
E (musical note) in pieces where E is in the key signature, in order to represent a diatonic, rather than a chromatic semitone; writing an E with a following E is regarded as a chromatic alteration of one scale degree. E (musical note) E is the third note of the C major scale, and mi in fixed-do solfège. It has enharmonic equivalents of F♭ (which is by definition a diatonic semitone above E) and D, amongst others. When calculated in equal temperament with a reference of A above middle C as 440 Hz, the frequency of Middle E (E) is approximately 329.628 Hz.