Frequency response of UK mobiles

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.

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"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

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

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.