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It's a very common sound but I've never thought to question why it happens.

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  • \$\begingroup\$ You mean the three sets of three chirps? \$\endgroup\$ – Ignacio Vazquez-Abrams Aug 30 '12 at 4:28
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    \$\begingroup\$ A layman explanation (from a layman) is that it is due to RF interference. The circuit that powers your speaker acts as an antenna and "catches" the mobile phone RF communication. This interference adds onto the normal audio that your speakers are playing. \$\endgroup\$ – icarus74 Aug 30 '12 at 4:31
  • \$\begingroup\$ Yeah, I think that's the one. But it ends with a longer buzzing sound \$\endgroup\$ – Sean Southern Aug 30 '12 at 4:31
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    \$\begingroup\$ Is it a standard protocol among all phones or do some phones make a different sound when connecting? \$\endgroup\$ – Sean Southern Aug 30 '12 at 4:35
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    \$\begingroup\$ Possible duplicate Why does GSM cause speakers to buzz? \$\endgroup\$ – MikeJ-UK Aug 30 '12 at 7:51
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I assume that you have a GSM phone.

When the GSM protocol was developed, they overlooked the fact that a "frame rate signal" in the protocol caused modulation of the RF signal at a consistent audio frequency rate with very clean consistent periods with and without RF. The GSM system was so important and so much had been spent on it that the allowed this defect to continue even though it would have been unacceptable in any equipment submitted for approval by the normal means.


That this was a complete mistake and completely unknown until late in the development is described here in Chapter 22 - Unintended Consequences of "Inside the Mobile Revolution" - a history of GSM. The writer is 'Stephen Temple CBE*', one of the few big-fish in the introduction of GSM**, arguably the UK's leading 'player' and, the text leads you to think, responsible for GSM being much of what it became.

He makes a very clear and open statement about what happened - and how it was unacceptably bad technically BUT unable to be stopped politically.

ST's bio page here

"INSIDE THE MOBILE REVOLUTION" is


**.

From the foreword:

  • The GSM 1800 MHz (PCN) element was added a few years later when the UK's DTI was at the leading edge of telecommunications liberalisation and I propelled it to be the first credible entity to set out the vision of the personal mobile phone as a consumer product (‘Phones on the Move’) and put forward the conditions to make it happen. My election as Chairman of the Technical Assembly of the European Telecommunications standards Institute in 1988 then provided an excellent vantage point as GSM went through its transition from a policy to a new born infant digital mobile industry. All this left me sitting on a unique (although in parts partial) account of how GSM came to be the mobile radio equivalent of the cosmic “big bang” and one of Europe's most successful high technology projects.
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  • \$\begingroup\$ Wow. Hearing this very interesting bit of information for the first time. Since GSM "modulation" schemes have evolved over time, wondering if the frame-rate signal got modulated resulting in similar behaviour ? \$\endgroup\$ – icarus74 Aug 30 '12 at 5:00
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    \$\begingroup\$ So, you're saying that the carrier is being keyed at an audio rate, essentially resulting in an AM signal modulated in the audible range? Then you declare this to be a mistake? Maybe it's unfortunate; maybe it's serendipitous (depends on your point of view), but is it technically wrong? \$\endgroup\$ – gbarry Aug 30 '12 at 6:15
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    \$\begingroup\$ @gbarry It's wrong. ie it was a technical oversight during design that was missed until well into the implementation phase. They had enough clout to be abl;e to get away with it. Few others would have. \$\endgroup\$ – Russell McMahon Aug 31 '12 at 16:10
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    \$\begingroup\$ @Russel Wow, that's a fun fact. Do you know where could one find more information about past GSM development? \$\endgroup\$ – Sean Southern Sep 1 '12 at 4:51
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    \$\begingroup\$ Particularly unfortunate for people wearing hearing-aids. Hearing aids are often designed to pick up RF signals at audio frequencies: this is the 'audio loop' system used so hearing-aids can pick up direct audio from public-address systems in churches, railway stations, etc. Just for its effect on partially deaf people, GSM would never pass approval. \$\endgroup\$ – david Jun 11 '13 at 5:53
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It's because the electromagnetic waves, sent by cell phone interfere with speaker circuit.

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