Have a look at this fantastic website that has examples of the sounds instruments make in an orchestra. Vital listening.
These are brass instruments. Trumpets, French Horn, Trombone, Tuba (in the middle). Tuba has the lowest pitch. Get used to the sound. Oh, and this is a brass quintet (5 brass instruments).
Brass instruments might use a mute to change the sound. Watch this to see how they work, and how the sound (or timbre) is different.