The decision whether to specify pitch or not (for a given sound source) is one of the first decisions to make in preparing a score in Global Notation, because it helps us decide what layers to use, and hence, how to set up the “manuscript paper” (see Unspecified pitch). So far, we have used only examples with unspecified pitch to introduce ways of specifying onset timing and duration. But as the use of definite pitch is obviously important in a lot of music, we will need to be able to specify pitch as well.
Pitch means how high or low the sounds are; but this is really two distinct questions. One question is how high or low a sound is in relation to some absolute standard for measuring pitch. For instance, “middle C” on the piano is always the same pitch regardless what music it’s used in. This means that in calling a certain sound “middle C” we are speaking of its “absolute pitch.”
The other question is how much higher or lower one sound is than another within the same piece of music. For instance, in the do-re-mi system, re is always higher than do by the same amount, even though the absolute pitch of both re and do will depend what “key” the music is performed in. To say that a piece is in the “key of C” means that C is do for that piece; re will then be D, and so on up the scale. But if the same piece is performed in the key of F, do and re will be F and G respectively. The relationship between do and re doesn’t change. This means that in calling a certain sound do or re (or mi, fa etc.) we are speaking of its “relative pitch.”
When the same piece of music is performed in a different key, the absolute pitch of every note is changed, but because they are all changed by the same amount, the relationships between the pitches stay the same. Because of this, for most listeners, the music sounds much the same in different keys. (Singers often take advantage of that fact by changing the key of a song to suit their own voice range.) On the other hand, even a small change in relative pitch, such as singing mi instead of re, can feel as if a different song is being performed.
All of this suggests that relative pitch is far more important to the effect of music than absolute pitch, and ought to be directly specifiable in our Global Notation system. Staff notation specifies relative pitch only indirectly, by specifying absolute pitch for every note (from which relative pitch can be inferred). But in Global Notation, absolute pitch, like anything else, is specified only when wanted, and relative pitch can be specified without it. We will therefore deal with the specification of absolute and relative pitch separately.