[foo_barrio]

Bells and metal tubes all can have funky harmonics too (and sub harmonics which is interesting). I don't know if it qualifies as "timbre" but if you remove the initial attack, many instruments sound very similar. There are some tests on youtube that I did a lot worse than I thought I would.

[genewitch]

One of my go-to for making a new instrument sound is to tamper with the ADSR envelopes, the attack (as you say, the first part, like a pluck of a string or mallet hitting a bell), decay, how long the note "fades" naturally, sustain which is the total length of a note, and release, which is how long a note plays after you "release" it.

Turning the attack up removes the pluck, setting the other three short makes anything percussive, and you can get weirdness if you mess with decay and release with echo / delay effects.

I should sleep, this was way harder to explain than it should have been.

Example, harp has a sharp attack, and real long decay, sustain, and release. To make that a pizzicato violin, you snap the decay and sustain to nothing, and leave a little release. Now your harp sounds like a violin.