there are also extant many, many reports, lots from newspapers, that are
reviews of Twain's performances -- and many of these make very specific
remarks about his "sound" and so on.

many of these kinds of reviews are quoted in books on Twain's lecturing,
such as Fatout's _MT on the Lecture Circuit_.

There are, by the way, numerous recordings of James Whitcomb Riley, the
public performer that Twain especially esteemed.  Perhaps those might give
a clue regarding Twain's style, sound, and delivery.  Twain was known to
perform some of Riley's poems on occasion. . . .

--Hal Bush