Falt is an altered dominant: it keeps the root, major 3rd, and flat 7th of , then changes upper notes. This page spells it F, A, Eb, G# and Db.
Here the altered notes are and . “Alt” is a family name, so another usable voicing can choose different alterations.
Also written F7alt, F7altered or F altered dominant.
Falt in 3rd inversion puts Eb in the bass instead of F, the 7th of the chord. The notes are the same; what changes is what the bass line does, which is most of why you would reach for it — it lets the lowest voice move by step where the root would have jumped.
2 of Falt’s 9 shapes do this:xx1224x6769x
Alt is not one chord but an instruction: a dominant with its ninth and fifth altered. Its usual home is between Cm7b5 and Bbm6, where the ♭13 is already the minor third of the chord it resolves to.
Listen for: The ii’s minor third falls a whole step to the V’s ♭13, which holds as the minor third of the i.
In a major key Falt works as the V of the ii: Abmaj7, Falt, Bbm7, Eb7. Its ♭13 is the minor third of the ii it leads to.
Listen for: The top voice rises a half step to the ♭13 and then stays put: minor third of the ii, flat seventh of the V.
Contains Falt and adds flat ninth and flat fifth.
The common shapes and the derived voicings come from different places, and both are explained in how this site is built.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.