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Frequency Range of phone line (Cell?)

Howdy! I'm not /entirely/ sure this is the right place to ask; I narrowed it down between here and alt.sci.physics.acoustics, and this seems more your ballpark.

A buddy and i were talking about alpha waves and suggestibility, and he wanted to know; is it possible to broadcast a 7-cycle-per-second tone (alpha wave inducing) over a phone line? Could it be quiet enough to be below your level of conscious awareness?

What's the frequency range of a household telephone? A cell phone? Do they cut off at the audible range?

I've noticed that a 7 cycle tone played through nice 6cm ceiling- mounted speakers is inaudible in a normal sized room below a certain decibel level while still having the normal effect (i.e. a glaze-over/ zoning out.) I assume this is perceptual drop-out, but the same tone remains audible through headphones. (Not soft enough?)

So, yeah... Audio range of phones in terms of frequency and volume (dynamic range?)

Uh, to make this slightly less creepy, the reason we were discussing this was for a story, so a pseudo-science answer will probably do. ;-) Though an actual-science answer would be interesting too.

-Derik

Reply to
regenesis0
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The frequency response of telephone and communication equipment is usually in the range of 300 to 3000Hz. It's a rule of thumb but may vary with specialized equipment. A 7 Hz signal is difficult to reproduce with small speakers and conventional audio equipment. I've hooked up audio signal generators to amps and speakers before and watched the woofer cone move back and fourth in response to very low frequencies. It sounds like a motorboat and I doubt a 7 Hz signal could make it through a telephone network.

[8~{} Uncle Monster
Reply to
Uncle Monster

The most obvious thing that comes to my mind is to have an audio frequency carrier, modulated by the 7 Hz. There might still be a problem with a digital cellphone, as they use compression (Adaptive PCM)?. I don't know what the highest continuous single frequency tone is that you could get through a, say, GSM phone.

Tam

Reply to
Tam/WB2TT

If the connection is over a digital ISDN circuit the answer is DC to almost 4kHz (provided the right terminal equipment, such as an ISDN adapter in a PC is used). This may change on some international circuits using compression, but I have successfully transmitted DC coupled signals across Europe and to the USA from the UK.

GSM mobile phones vary according to which codec is in use. The standard full and half rate GSM codecs attenuate DC by only a few dB (the high pass filter defined in the GSM specification is broken). The enhanced family of GSM codecs fix the broken filter and high-pass at about 80Hz. In all cases the low-pass is at around 3.7kHz, depending on the exact characteristics of the anti-aliasing filter in the ADC used in the handset.

However, it can be difficult to transmit sustained tones through GSM transceivers (especially handsfree) because noise suppression algorithms detect and suppress constant tones.

John

Reply to
jrwalliker

This is all very fascinating, thanks guys!

-Derik

Reply to
Derik

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