I have been working on the excellent book 'Melody' by Rikky Rooksby. There is some work on suspended chords and one example on a score showed the chord Fsus♯4. Now, working on the definition that on a suspended 4th the 4th replaces the 3rd by the note that is one high higher in the scale got me puzzled. Is this correct, is there such a thing and, if so, how? I thought it would be just Fsus4. After all the 4th note on the scale will just that, no matter what scale.
Fsus♯4 should be
F B♮ C.
Fsus4 would be
F B♭ C.
In terms of the chord/scale system
Fsus♯4 would be matched up with some kind of Lydian scale.
F is the tonic and the
B actually resolved, I would expect the
B♭ to go down to an
A and the
B♮ to go up to the
C. That upward resolution can be called a retardation instead of a suspension. Anyway, in pop and jazz chords with
sus labels are often not treated as real suspensions, so these details may not matter.
It might be a misprint for F#sus4. It might be a loose description of F(add♯4) or even F(♭5).
If you show us the page in question, it might be clear which is intended.
As you've seen from answers and comments so far, it's unclear as a chord symbol and therefore its use is not to be recommended.
Not a chord I've ever come across. If indeed it is Fsus♯4, then its spelling will have to be F B C. As that stands, the B and C will technically be next to each other - otherwise that B would be named as ♯11. It's not, and the 3rd (A) would be retained. Although it wouldn't be the first time a chord has been incorrectly named..! Which I doubt sounds too good, anywhere.
Googling gives some examples of 'Fsus♯4, which turn out to be, unsurprisingly, F♯sus4, which gets spelled F♯ B C♯. Altogether more listenable! Dependant on the key and location in the piece, I'm going for the latter!
EDIT: another thought occurred - in key C, with a G note as bass, it sounds like a sus, playing FBC close in treble. That resolves nicely to C, by dropping the B to A, then change to C major, as a lot of sus chords actually do. But I wouldn't call it Fsus♯4. More like G11.