I'm trying to learn how AM radio communication works. If I understand correctly, an AM radio signal transmits on a fixed frequency, using the amplitude of the wave to transmit the frequency of the sound. However, this only carries the frequency of the source sound, not the volume. So if you're transmitting voice, how is a whisper quiet and a scream loud? Why wouldn't they be the same volume?
The audio signal to be transmitted varies the amplitude of the transmitted signal.
The frequency of the amplitude variations correspond to the modulating audio frequency.
The size of the amplitude variations transmit the volume - a loud sound will produce a large amplitude variation at the transmitter. The receiver will, in turn, produce a loud sound on receiving a large amplitude variation.