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Re: [microsound] Dumb tech ?




I can confirm that when my mobile phone is too close to amplification systems I get the exact same noises. Most noticeable for me is on my car stereo tuned while tuned to around 90Mhz. Its probably because my phone pocket is very close to the tuner / amplifier while I am driving.

Here is more info:

From: http://www.edn.com/index.asp?layout=article&articleid=CA498768

"Energy in the audio-frequency range, including the 217-Hz TDMA pulse- repetition rate and its harmonics, exists in the phone in two forms: as variations in the dc-supply current and as the RF signal's modulation envelope. The dc-supply current pulse waveform comes from the large current that the RF power amplifier draws during transmission time slots and the smaller current that the RF circuitry draws during the receive interval (Figure 1). These currents rise atop a varying baseline current that the phone draws for the processor and audio section that continues even while the RF circuitry is turned off to save energy between time slots.

The 217-Hz pulse waveform produces an audible buzz when it couples into the audio path and conducts to the speaker, earpiece, or microphone. The two primary mechanisms for coupling the current waveform into the audio circuits are supply and ground ripple, both at the 217-Hz rate. Additionally, a portion of the transmitted RF energy can couple into the audio circuits. The audio section can rectify the RF signal, which extracts the waveform envelope in the way an AM detector would. A Fourier analysis of the periodic narrow pulse shows the 217-Hz fundamental and its harmonics—the typical TDMA- buzz spectrum (Figure 2)."




On May 7, 2008, at 3:10 PM, Christoph Fuegenschuh wrote:

ho,
a mobile phone?
best,
C.
Am 07.05.2008 um 21:01 schrieb Charles Turner:

Hey all-

Does anyone know what causes this?

<http://www.citymus101.net/speakerglitch.wav>

A couple  of years ago, I used to hear this occasionally on my stereo
speakers, with CB-radio talk accompanying it. Now it's spread to my
studio speakers, my mother's kitchen radio and NYC taxi cabs. It's also
far more frequent, which I'm starting to find annoying, all Cage-ing
aside.

Of course the next question is what to do about it. (Aside from
featuring it.)

Thanks, Charles


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