The transmission channel changes from acoustic path to electrical system in device-mediated speech.

Evidence

In speech communication without electrical devices, the transmission channel is the acoustic path from the lips of the speaker to the ears of the listener. When electrical devices are used, a microphone and a headphone and loudspeaker are needed together with an electrical transmission line, possibly with coding and transmission technologies. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 2382