I believe I heard somewhere, perhaps from the Chamberlain, Willi, and
Ouchterloney lawfirm that handled the estate or from Holbrook's agent that
he
met with Clara Clemens  and asked her about the voice after working on it.
I
don't know the sequence of events but as I understand it, she told him it
was
the closest thing to her father's voice that she had heard.

Jerry O'Brien