Hi, On 06/13/2017 07:04 PM, jonetsu wrote: > > Yes, that's the case. Just to add to this a tiny bit, cell phone > waves are way up there in the frequencies, so that cannot make such a > low pulsating interference. Not sure, but it seems that the cell phone > waves are modulated in the (very) low frequency range and that > modulation is what's picked up by the (magnet of the) speakers. That > modulation creates another frequency. I'll explain some related GSM basics below, but keep in mind that this is a quite simplified description. GSM RF transmission is basically done in bursts with a length of ~ 0.5 ms each. These are organised in frames of 8 timeslots. If the phone needs to send data (either audio, data, acknowledgements, control messages), it requests a channel from the network which allocates an uplink timeslot for the phone. Since each burst may only carry a few bits (normal burst: 114 data bits brutto minus forward error correction), you'll need some of them which gives you a sequence of bursts at a rate of ~ 250Hz (-> audio base frequency). Initially, when the phone tries to set up a connection it sends a sequence of so-called RACH bursts on different timeslots with a higher RF power level (involving some allocation randomness to have a chance to get a free slot even if another phone tries to do it at the same time). So it sounds differently at the start of the connection. The transmission power of your phone can be reduced by the base station later on, so there can be an audible power reduction step depending on the distance to the base station. Things get more complicated with GRPS/EDGE (which can also be used for SMS transmission) because the slot allocation for packet data can be more dynamic. If you combine this with a non-linear receiver you just get AM demodulation of the burst sequence sent by your phone giving you exactly this kind of sounds. Jacob _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
