C#alt is C#, E#, B, E and A — with every tension it can carry altered at once.
It sounds maximum tension, barely holding together. Not one chord but an instruction: take the root, third and flat seventh, add any two alterations, and let the rest go.
Altered dominant — the hardest pull available.
Also written C#7alt, C#7altered or C# altered dominant.
Stack the four notes closely, then drop the second voice from the top an octave. It typically lands on four adjacent strings: the guitar’s workhorse voicing.
That result, 5–R–3–7, is the shape usually meant by drop 2. Named by its bass note, as the inversions are here, it is the 2nd inversion.
Alt is not one chord but an instruction: a dominant with its ninth and fifth altered. Its usual home is between G#m7b5 and F#m6, 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 C#alt works as the V of the ii: Emaj7, C#alt, F#m7, B7. 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.
Every note of C#alt is in C# altered.
Each of those is a page: the scale across the neck, and the chords it harmonises into — which is where C#alt sits in it. Every scale.
Change one note of C#alt and you have (drop the sharp ninth), (the sharp ninth becomes the ninth) or (the flat thirteenth becomes the fifth).
C#alt is an altered chord — a dominant seventh with its fifth or ninth moved. Altered dominant chords on every root.
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.