Cytowic calls sound → color synesthesia "something like fireworks": voice, music, and assorted environmental sounds such as clattering dishes or dog barks trigger color and simple shapes that arise, move around, and then fade when the sound stimulus ends.
One synesthete says, "T’s are generally crabbed, ungenerous creatures. U is a soulless sort of thing. 4 is honest, but… 3 I cannot trust… 9 is dark, a gentleman, tall and graceful..."
"Whenever I hear, read, or articulate (inner speech) words or word sounds, I experience an immediate and involuntary taste sensation on my tongue. These very specific taste associations never change and have remained the same for as long as I can remember."
GUYS. SYNESTHESIA IS BLOWING MY MIND.