rself from Fig. 83 which shows the tongue positions for
three different vowel sounds. You can see also from Fig. 84, which shows
the mouth positions for the different vowels, how the size and shape of
the mouth cavity is changed to give different sounds. These figures are
in Pl. VIII.

The pitch of the note need not change as every singer knows. You can try
that also for yourself by singing the vowel sound of "ahh" and then
changing the shape of your mouth so as to give the sound
"ah--aw--ow--ou." The pitch of the note will not change because the
fundamental stays the same. The speech significance of the sound,
however, changes completely because the mouth cavity resonates to
different ones of the higher notes which come from the larynx along with
the fundamental note.

Now you can see what is necessary for telephonic transmission. Each and
every component note which enters into human speech must be transmitted
and accurately reproduced by the receiver. More than that, all the
proportions must be kept just the same as in the original spoken sound.
We usually say that there must be reproduced in the air at the receiver
exactly the same "wave form" as is present in the air at the
transmitter. If that isn't done the speech won't be natural and one
cannot recognize voices although he may understand pretty well. If there
is too much "distortion" of the wave form, that is if the relative
intensities of the component notes of the voice are too much altered,
then there may even be a loss of intelligibility so that the listener
cannot understand what is being said.

What particular notes are in the human voice depends partly on the
person who is speaking. You know that the fundamental of a bass voice is
lower than that of a soprano. Besides the fundamental, however, there
are a lot of higher notes always present. This is particularly true when
the spoken sound is a consonant, like "s" or "f" or "v." The particular
notes, which are present and are important, depend upon what sound one
is saying.

Usually, however, we find that if we can transmit and reproduce exactly
all the notes which lie between a frequency of about 200 cycles a second
and one of about 2000 cycles a second the reproduced speech will be
quite natural and very intelligible. For singing and for transmitting
instrumental music it is necessary to transmit and reproduce still
higher notes.

What you will have to look out for, therefore, in a receiving set is