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Frequency Range of phone line (Cell?)

Discussion in 'Electronic Design' started by [email protected], Dec 12, 2007.

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  1. Guest

    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.

  2. 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
  3. Tam/WB2TT

    Tam/WB2TT Guest

    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.

  4. Guest

    What's the frequency range of a household telephone? A cell phone?

    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.

  5. Derik

    Derik Guest

    This is all very fascinating, thanks guys!

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