Every crowd has its several tones

• every crowd has... → ECH = HCE

• every cloud has a silver lining: (proverbial)

• crwth: a Welsh fiddle, continuing the musical foliation in this paragraph

• crowd: an alternative name for the Welsh crwth

• chord: (music) a harmonic combination of two or more tones, continuing the musical foliation in this paragraph

• As I Was Going to St Ives: (nursery rhyme) “As I was going to St Ives, I met a man with seven wives, and every wife had seven ....”
  • Wikipedia

• Pont de Sèvres; a bridge in Paris
  • A Finnegans Wake Gazetteer

• tone: a musical note, continuing the musical foliation in this paragraph

Commentary

This phrase 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 ("trade") 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 und Isolde.

• Wikipedia

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