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The 4th valve on a euphonium lowers the fundamental pitch by 2 1/2 steps, or from Bb to F. Because it is compensating it also effectively adds tubing to each valve slide for the other valves when used in combination with the 4th valve so that they have the equivalent length that they would if it were really in F, and not just a Bb horn playing an F. Therefore a compensating euphonium with the 4th valve down is effectively a euphonium in F.

I thought it was because they were spelled euFonium!

(Don't even get Joe started on euphonium vs. baritone vs barifonium vs. euphimism)

EuphoniumDude wrote:So its like a whole new fingering system?

The fingerings for a compensating euph is different than a non-comp euph when the 4th valve is used. The compensating system adds extra tube length. i.e.

Note, comp fingering, non-comp fingering
F, 4, 4
E, 24, 24 (non-comp is slightly sharp)
Eb, 14, 124 (non-comp is about 30 cents flat)
D, 124, 234 (non-comp is about 12 cents flat)
Db/C#, 234, 134 (non-comp is 20 cents sharp)
C, 134, 1234 (comp is 15 cents sharp, non-comp is about 50 cents sharp)
B, 1234, not playable (comp is sharp)

Regards,
Bob

EuphoniumDude wrote:So its like a whole new fingering system?

Not really. The compensating 4th value lets you play chromatically down from the low F below the staff to the pedal Bb using the same fingerings you would for the notes going down from the F in the staff to the 2nd line Bb. Its like getting an additional usable partial (low F) when you hold the 4th valve down.

The 4th valve (compensating or non) also give you an in-tune alternate for the 1-3 combination you use on the 2nd space C and then some other alternate fingerings for the various other quirks your horn may have above that.

As Bob's post above points out, even the compensation is not perfect but it does allow you to use the same fingerings for both octives.

--paul;

(edited misquote)