How Does a Radio Broadcast Get From the Microphone to Your Speakers?
Radio can feel like magic: someone speaks into a microphone across town, and their voice comes out of a box in your kitchen. It is not magic; it is a chain of well-understood steps, and each one is simple on its own. This page walks the whole chain, from the announcer's mouth to your speaker, for both over-the-air radio and internet streams.
Step 1: Sound Becomes Electricity
Everything starts at the microphone, which is a transducer, a device that converts one form of energy into another. The diaphragm inside the mic vibrates with the arriving sound, and the microphone turns those vibrations into a small electrical signal whose variations mirror the sound wave. How it does that depends on the design; Shure's educational publication on microphone techniques describes the two main families, dynamic and condenser, which we compare in our broadcast microphone guide. From this point on, the voice exists as an electrical signal, and everything downstream works with that signal.
Step 2: The Signal Gets Mixed
A real broadcast is rarely one microphone. Music, station identifications, phone guests, and multiple hosts all arrive as separate signals, and a mixer combines them into a single program feed at balanced levels. In a hobby studio this might be a small hardware mixer or software on a laptop; in a professional station it is a large console; the job is the same.
Step 3: The Signal Rides a Carrier Wave
Here is the genuinely clever part. An audio signal cannot usefully be flung across a city on its own, so the transmitter generates a steady high-frequency radio wave, called a carrier, and impresses the program signal onto it. PBS's interactive explainer on radio transmission shows the two classic ways of doing this. In amplitude modulation, or AM, the strength of the carrier wave is varied in step with the audio. In frequency modulation, or FM, the carrier's strength stays constant and its frequency is varied instead. The information is identical; only the property of the wave used to carry it differs. This single distinction is the root of the practical differences listeners notice between the two bands, which we unpack in AM vs. FM: what's actually different?
Step 4: The Receiver Undoes It All
Your radio's antenna is bathed in signals from every station at once. Tuning selects one carrier, which is what the numbers on the dial identify, something we explain in what the numbers on a radio dial mean. The receiver then reverses the modulation, recovering the original audio signal from the carrier's variations. That recovered signal drives a speaker, whose cone vibrates and recreates the sound: the microphone's job run backwards.
This is also where static enters the story. As the PBS explainer demonstrates, electrical interference adds unwanted spikes to a wave's amplitude. An AM receiver, which reads amplitude as information, reproduces those spikes as crackle. An FM receiver reads frequency and can disregard amplitude disturbances, which is why FM sounds cleaner in the presence of interference.
What Changes With an Internet Stream
An internet station keeps steps one and two exactly as described and swaps the rest. Instead of a transmitter and carrier wave, an encoder compresses the program feed into a digital stream and sends it to a streaming server, which relays a copy to each listener over the internet. The listener's app decodes the stream back into an audio signal for the speaker. No carrier, no antenna, no geographic range limit, which is a large part of why internet radio is the accessible entry point for beginners.
The Chain at a Glance
- Microphone: sound in, electrical signal out
- Mixer: many signals become one program feed
- Transmitter or encoder: the feed is modulated onto a carrier, or compressed into a stream
- Receiver or app: the process runs in reverse
- Speaker: electrical signal becomes sound again
Every link is a translation, and the voice that comes out of your kitchen radio is the end of a round trip that began as vibrating air in front of a microphone.