Crowd

crowd = chord

trade = triad

This appears in an allusion to music:

"every crowd has its several tones and every trade has its clever mechanics and each harmonical has a point of its own, Olaf's on the rise and Ivor's on the lift and Sitric's place's between them"

The triad is the rudiment of western harmony: three notes forming a chord, consisting of a first, a third (flat or natural, i.e., major or minor), and a fifth (natural/perfect, augmented, or diminished).

Apparently, Ivor = the first, Sitric (a name containing "tri") = the third, and Olaf = the fifth: first-third-fifth on a keyboard is, visually, left ("on the lift") middle ("place is between them") and right ("on the rise").

Intriguingly, placed in that order, Ivor-Sitric-Olaf creates the acronym "ISO."

ISO my refer to Isolde. The myth of Tristan and Isolde is frequently referred to in Wake (e.g., page one: Tristram). And . . .

Perhaps the most famous chord in music, at least in Joyce's time, was the so-called "Tristan chord" -- the first chord in Wagner's opera "Tristan and Isolde". (To verify its fame, see http://www.answers.com/%22Tristan%20chord%22 )

Perhaps in response to the "Tristan chord", Joyce here creates an "Iso" chord.