Theres people on this forum talking about their range and mentioning `double Cs` as (usually) really high notes. Do you guys mean 2 octaves above middle C (as in, 2 ledger lines on a trble clef) or 3 octaves?

ok as far as I understand you have the middle c...your tunning note(if you play trumpet)but anyways jump up one octave up to high c which is 2 leger lines above the treble clef --0--(c) now you have this
-----(a line) you take it up one more octave above
---------------(f) this high c. This my friend would be
---------------(d) as far as I know the double c
---------------(b)
---------------(g)
---------------(e)

---0--- c
------- a
------------f
-------------d
------------g
-------------e

sorry about the mess up on the last post my comp was be`n a jack*** :P

If ya want to know what it sounds like here is a clip of a pro in florida.

http://screaminbill.com/library/bill%20carmichael%20-%20olympics.mpg

a double c is the high c up the octave. The first c above the staff up the octave. Its also known as the grand c.

What you mean is a double high c (c4 oder c````). This is a tone you pretty sure never will be able to produce on your horn...