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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?

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    \$\begingroup\$ A stands for amplitude... \$\endgroup\$ – old_timer Aug 29 '16 at 0:42
  • \$\begingroup\$ Have you seen any samples? They are all over the web. Start with a carrier wave, which has a certain amplitude. This amplitude is then modified directly by the audio signal, with associated gain in between. This is called "modulation" and it modulates the amplitude, which is why it is called AM. \$\endgroup\$ – jonk Aug 29 '16 at 0:42
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    \$\begingroup\$ Re -> " If I understand correctly, an AM radio signal transmits ... using the amplitude of the wave to transmit the frequency of the sound. -> Your understanding is incorrect . **AMPLITUDE": modulation. Look it up, if necessary. \$\endgroup\$ – Russell McMahon Aug 29 '16 at 1:10
  • \$\begingroup\$ The "modulation depth" carries the amplitude. \$\endgroup\$ – Brian Drummond Aug 29 '16 at 10:13
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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.

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  • \$\begingroup\$ OK, thanks! I was thinking that the source audio had an amplitude and a frequency much like the carrier wave, guess I forgot how audio works. The frequency of the audio is oscillations in the amplitude. \$\endgroup\$ – user112513312 Aug 29 '16 at 6:16

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