The double action pedal harp

Ravel (left) and Lily Laskine (harpist) probably in the mid 1920s
I'll just leave a few breadcrumbs for you to follow. 

Albert Blondel was director of Maison Érard in Paris

This is really a musical commercial for Maison Érard

Harp music for a pedal harp......egad, key of g-flat. - why g-flat?

this is the real deal - written in a few days.....

It's an interesting story and the clues will take you through it.