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  1. #1
    Lem
    Guest
    What sort of audio frequency range can be sent from one mobile across
    the network(s) to another mobile?

    To be clear what I mean, if I compare landline phones then they can
    transmitt/receieve something like 300 Hz to 3,400 Hz.



    See More: Frequency response of UK mobiles




  2. #2
    harrogate3
    Guest

    Re: Frequency response of UK mobiles


    "Lem" <[email protected]> wrote in message
    news:[email protected]
    > What sort of audio frequency range can be sent from one mobile

    across
    > the network(s) to another mobile?
    >
    > To be clear what I mean, if I compare landline phones then they can
    > transmitt/receieve something like 300 Hz to 3,400 Hz.
    >


    Traditional 'telephone' response has always been 300-3400, although
    over the last decade or two this has shrunk to 300-3000 or in practice
    300-2500.

    I suspect it would be difficult to make any quantitative assessment of
    the response of a digital phone circuit due to the processing that
    goes on in the handset. A 64Kb path (which is a 'telephone' circuit
    when digitised) is the norm, but some operators - certainly Orange -
    double sample so that the audio path per user is only 32Kb. This means
    that if the sample rate is maintained then the audio response is
    halved, or if the sample rate is reduced then the audio quality must
    suffer.

    A real can or worms this one.


    --
    Woody

    harrogate3 at ntlworld dot com





  3. #3

    Re: Frequency response of UK mobiles

    The answer for landlines in Europe is generally DC to 4kHz. The
    limitations come from the codecs at the transmitting and receiving ends
    of the connection which may be at the telephone exchange for an
    "analogue" line or in the subscriber equipment for an ISDN connection.

    If the terminating equipment at each end is an ISDN interface card in a
    PC, then it is normally possible to send a dc-coupled signal with 4kHz
    bandwidth across the UK, Europe and even to the USA. Within Europe -
    the audio signal is usually exactly the same as that which was
    transmitted. For transatlantic calls there is u-law - A-law
    conversion.

    Given the transparent infrastructure, GSM mobile calls are mostly
    dependent on the particular codecs used for each end of the call and
    the echo cancellers which the network operators use.

    The GSM advanced series of codecs have a high-pass filter at 80Hz,
    while the low-pass filtering is dependent on the anti-alias filter of
    the ADC in the phone. A low-pass corner frequency of around 3.7 or
    3.8kHz is common.
    The GSM standard-rate codecs have a bug in the specification such that
    the high-pass filter does not significantly block dc. This means that
    the actual response will depend on how the manufacturer has chosen to
    implement their design.

    Network operators sometimes choose different codecs from among those
    supported by the phone so as to provide the best audio quality when the
    network is not very busy and allow degraded quality but more calls when
    the network is congested.

    Other issues are variations in the uplink gain that various mobile
    network operators have set - there is a variation of at least 10dB from
    the "quietest" to the "loudest" across Europe. Some operators also
    apply automatic gain control which can interact in interesting ways
    with the processing in the phones.

    When making such measurements on mobile phones it is essential to use
    specially constructed test signals, because a constant tone will be
    removed by the noise suppression software in the phone after a short
    time.

    Just to add to the confusion, the word "codec" has two meanings here.
    In the GSM context it is the software which encodes the speech using a
    lossy compression scheme, whereas in the landline context it is the
    combined ADC/DAC which also includes bandpass filtering and A-law or
    u-law "logarithmic" amplitude compression.

    John




  4. #4
    JW
    Guest

    Re: Frequency response of UK mobiles

    Lem wrote:
    > What sort of audio frequency range can be sent from one mobile across
    > the network(s) to another mobile?
    >
    > To be clear what I mean, if I compare landline phones then they can
    > transmitt/receieve something like 300 Hz to 3,400 Hz.


    Standard network codecs are all narrowband, so they'll all
    sample at 8kHz, which limits the upper frequency. I think
    you can get wideband terminals, but they would be making
    data calls.



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