The long version.
Double consonants are a
peculiar and sometimes baffling aspect of Italian.
First of all, the local
"accent" in many regions totally ignores double consonants, for
instance in the Veneto region (capital Venice,) but this is also true, to
some extent, for the entire North.
In the South, the
tendency is the opposite, namely people tend to double consonants that
do not appear in the written version. The extreme case is the island of
Sardinia. To a Northern ear, it sounds like in the speech of Sardinians, all consonants are doubled.
How is the 'double'
consonant sound produced?
With letters such as L,
R, M, N, S, F, it "appears" as if it is sufficient to prolong the sound
a little more. But with sounds like B, P, T, D, G, C, J, and ch,
it is impossible to extend the sound.
IN REALITY, double
consonants are simply a marker to indicate that the VOWEL that precedes
that sound is SHORTENED considerably, to about 1/2 the regular length of
the phoneme. The phonemic energy saved by shortening the vowel, is
unloaded "explosively" on the following consonant, giving the impression
of a doubling of the length, while in reality it is the vowel that is responsible
for the entire phenomenon.