The C on an alto saxophone sounds
like an Eb on a piano.
Likewise the D on an alto saxophone sounds like an
F on a piano, etc.
In order to play the same pitches
of a melody in the key of C on the piano, the alto sax
must play in its instrument key of A. The saxophone is
therefore a transposing instrument.
C- instruments (as I call
them in this Course) are non transposing instruments.
They
include all keyboards, guitar, bass, violin, flute, harp,
trombone, voice, piano accordion, mouth organ, etc. They
represent so-called Concert pitch.
Bb- instruments are trumpet,
clarinet, tenor sax and soprano sax.
When Bb instruments play
in their key of C (no flat or sharp), Concert pitch instruments
play in the key of Bb (2 flats).
When Concert key instruments
play in the key of C (no flat or sharp), Bb instruments play in
their key of D (2 sharps).
Eb- instruments are alto sax
and baritone sax.
When Eb instruments play in their key of C
(no flat or sharp), Concert pitch instruments play in the key of
Eb (3 flats).
When Concert key instruments play in the key of C (no flat or
sharp), Eb instruments play in their key of A (3 sharps).
The Key signatures of Eb instruments and C instruments are always
three flats or three sharps apart. The Bb instruments key lies
in between this range.