Method and apparatus for multi-pass speech recognition. An input device
receives spoken input. A processor performs a first pass speech
recognition technique on the spoken input and forms first pass results.
The first pass results include a number of alternative speech
expressions, each having an assigned score related to the certainty that
the corresponding expression correctly matches the spoken input. The
processor selectively performs a second pass speech recognition technique
on the spoken input according to the first pass results. Preferably, the
second pass attempts to correctly match the spoken input to only those
expressions which were identified during the first pass. Otherwise, if
one of the expressions identified by the first pass is assigned a score
higher than a predetermined threshold (e.g., 95%), the second pass is not
performed. Because the second pass is performed only when necessary, the
invention recognizes speech with a faster average speed for a given
accuracy in comparison to prior systems. Alternately, the first pass
results identify a characteristic of the spoken input. The characteristic
can be the gender of the speaker or a type of telephone the speaker is
calling from. In which case, the second pass speech recognition technique
is selected from a plurality of speech recognition techniques according
to the characteristic identified by the first pass. Because the selected
second pass technique is specific to the characteristic of the spoken
input, the second pass technique can perform speech recognition faster
for a given accuracy than a technique which is not specific.