How sound is recorded and played back
Physics · Key Stage 2 · The School
Capturing a vibration as a pattern
Recording sound starts with a microphone. It turns a vibration into a changing electrical signal, exactly as it does for a live phone call. That signal is then stored, on a chip, a disc, or a strip of tape in older technology. It is stored as a PATTERN — a kind of coded copy of how the vibration changed over time.
Turning the pattern back into sound
Playing a recording back reads that stored pattern. It turns the pattern into an electrical signal again, matching the original as closely as the storage method allows. That signal is sent to a loudspeaker. The speaker vibrates in exactly that pattern, pushing the air. It creates a genuinely new sound wave, one our ears cannot tell apart from a live one.
Why a recording is a copy, not the original
The actual sound wave from years ago is long gone. Sound waves do not survive being stored. What is stored is a pattern, describing how that vibration changed. A speaker later uses that pattern to build a brand new sound wave. A recording, however good, is a faithful re-creation. It is never the original wave itself, somehow preserved.
A grandparent's voice, recorded on tape decades ago, is played back today through a modern loudspeaker. The listener hears something that sounds remarkably like the original voice. But the original sound waves from that recording session vanished the instant they were made, the way any sound does. What survived was a pattern, stored on the tape. Today's speaker used that old pattern to create an entirely new sound wave, this instant, in this room. It is a faithful echo of a voice. It is not the voice's actual sound, somehow preserved across ten years.