You might not hear it much anymore, but the dreaded GSM buzz was a common annoyance a few years ago. Hold a GSM phone transmitting any kind of signal anywhere near a speaker, and suddenly the most unpleasant buzzing would start distorting your audio. This is a consequence of the way GSM works, but have you ever wondered why it works like this?

Before super-fast HSPA connections arrived on GSM phones, there was TDMA-based 2G EDGE. TDMA stands for time-division multiple access, and it’s the key to the distinctive GSM buzz. When your mobile device is talking to a cell tower, it’s not doing so on its own. There are probably dozens of other phones pinging the tower at that exact same moment. Since a limited number of phones can operate on a single frequency, TDMA informs the way devices take turns transmitting data.

All the action takes place in a TDMA frame, which is 0.004615 seconds long. So every 0.004615 seconds your phone gets its chance to transmit. Can you guess what else happens every 0.004615 seconds? Yep, the electronic interference that causes the GSM buzz happens in the same pattern.

buzz

The frequencies that GSM runs on also play into this situation. The audio amplifiers are being hit with bursts of electromagnetic energy from the phone because the wiring and circuitry acts as an antenna. Even headphone cables can be susceptible. The signal causes a small voltage spike that is translated into sound — that’s what a speaker does, after all.

Newer varieties of GSM technology are based on WCDMA technology and aren’t time-divided. Combine that with the prevalence of different frequencies and the GSM buzz is much less common these days. Still, you might hear it if your GSM phone steps down to 2G service. It’s the sound of nostalgia.

via Windytan