QUOTE(Maloperro @ Aug 18 2010, 10:35 AM)
I'm a beginner so correct me for any mistake..
normally the entire band will use the same tuning..
for example, my fav band, billy talent - the guitarist & bassist are using
drop D and if i'm not mistaken all of their song is using drop D.
I feel as if drop D is like a trademark for their music..

Hah! Finally found someone who also like Billy Talent!
To answer your question, it's better for the entire band to tune in the same key so they can play easier together as a band. You can mix up the two guitars one with standard and the other with drop D, but some chords can't be played on both guitars to have the exact tone and sustain. To illustrate:
Tuning: Standard
Emaj (bar chords)
e |---------------------------------------------------------------------------|
B |---------------------------------------------------------------------------|
G |---------------------------------------------------------------------------|
D |---2-----------------------------------------------------------------------|
A |---2-----------------------------------------------------------------------|
E |---0-----------------------------------------------------------------------|
Tuning: Drop D
Emaj (bar chords)
e |---------------------------------------------------------------------------|
B |---------------------------------------------------------------------------|
G |---------------------------------------------------------------------------|
D |---2-----------------------------------------------------------------------|
A |---2-----------------------------------------------------------------------|
D |---2-----------------------------------------------------------------------|
So, if you want to play D#/E flat bar chord in drop D:
Tuning: Drop D
D#/E flat (bar chords)
e |---------------------------------------------------------------------------|
B |---------------------------------------------------------------------------|
G |---------------------------------------------------------------------------|
D |---1-----------------------------------------------------------------------|
A |---1-----------------------------------------------------------------------|
D |---1-----------------------------------------------------------------------|
The guitar in the standard tuning
can't simply shift to the first fret like this:
Tuning: Standard
D#/E flat (bar chords)
*Wrong way*e |---------------------------------------------------------------------------|
B |---------------------------------------------------------------------------|
G |---------------------------------------------------------------------------|
D |---1-----------------------------------------------------------------------|
A |---1-----------------------------------------------------------------------|
E |---0-----------------------------------------------------------------------|
As simply stated, the above is
wrong way to play D#/E flat bar chord in standard tuning!
So the only way for the standard tuning guitar to play the same chords as per the guitar in drop D tuning is to go down one string, which is:
Tuning: Standard
D#/E flat (bar chords)
e |---------------------------------------------------------------------------|
B |---------------------------------------------------------------------------|
G |------8-------------------------------------------------------------------|
D |------8-------------------------------------------------------------------|
A |------6-------------------------------------------------------------------|
E |---------------------------------------------------------------------------|
Although the D#/E flat bar chord above is correct for standard tuning, you'll lose the heaviness of the tone if you had played it in drop D tuning.
The above is also the same for Bass tuning with a drop D guitar. Usually bass does not need to drop D since it can be substitute or replaced with a lower string, but again, you'll lose the heavy tone.
In the case of Billy Talent, the Bassist uses drop D tuning to get the heavy tones to match Ian D'sa's (Billy Talent's guitarist) guitar riffs.
Hope that helps!