We have found that choosing the right speaker to record, is actually as
important as all the the other processes we describe. Some people just
have better voices that are better for synthesis than others. In
general people with, clearer, more consistent voices are better than
others but unfortunately its not as clear as that. Professional
speakers are in general better for synthesis that non-professional. Though
not all professional voices work, and many non-professional speakers give
good results.
In general you are looking for clear speakers, who don't mumble and
don't have any speech impediments. It helps if they are aware of speech
technology, i.e. have some vague idea of what a phoneme is. A
consistent deliver is important. As different parts of speech from
different parts of the recorded database are going to be extracted and
put together you what the speech to be as consistent as possible. This
is usually the quality that professional speakers have (or any one used
to public speaking). Also note most people can't actually talk for long
periods without practice. Lectures/Teachers are actually much more used
to this than students, though this ability can be learned quite easily.
Note choosing the right speaker, if its important to you, can be
a big project. For example, an experiment done at AT&T to
select good speakers for synthesis involved recording fair sized
databases for a number of professional speakers (20 or so) and
building simple synthesis example from their voice and submitting
these to a large number of human listeners to get them to evaluate
quality [syrdal??]. Of course most of us don't have the resources
to do searches like that but it is worth taking a little time to
think of the best speaker before investing the considerable time in
takes in building a speaker.
Note that trying to capture a particular voice is still somewhat
difficult. You will always capture some of that persons voice but its
unlikely a synthesizer built from recordings of a person will always
sound just like that person. However you should note that voice you
think are distinctive may be so because of lots variation. For example
Homer Simpson's voice is distinctive but it would be difficult to built
a synthesizer from. The Comic Book Guy (also from the Simpsons) also
has a very distinctive voice but is much less varied prosodically than
Homer's and hence it iss likely to be easier to build a synthesizer from
his voice. Likewise, Patrick Stewart's voice should be easier than Jim
Carey's.
However as it is usually the case that you just have to take any speaker
you have willing to do it (often yourself), there are still things you
should do that will help the quality. It is best is recording is done
in the same session, as it is difficult to set up the same recording
environment (even when you are very careful). We recommend recording
some time in the morning (not immediately you get up), and if you must
re-record do so at the same time of day. Avoid recording when the
speaker has a cold, or a hangover as it can be difficult to recreate
that state if multiple sessions are required.
