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1200 baud data transfer over audio passband of cellphone. Is that possible?
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sv3ora:
So through wired phone there is no compression?
ogden:

--- Quote from: sv3ora on October 29, 2019, 10:50:37 pm ---So through wired phone there is no compression?

--- End quote ---
You are advised to search The Internet. Answer is all over the place.
coppice:

--- Quote from: ogden on October 29, 2019, 10:48:13 pm ---
--- Quote from: sv3ora on October 29, 2019, 09:48:55 pm ---Now, I do not know if this is due to the mobile phone codecs or the landline phone codecs

--- End quote ---
Landline usually have 8ksps @8bit PCM, no codecs. Who uses landline today anyway  :-//

--- End quote ---
Simple 8 bit samples would have a rather limited dynamic range for good audio transmission. Landlines have used a simple pseudo-logarithmic compression codec, G.711, since the very beginning of digitising the network in the late 1950s. The variant used in most of the world is called A-law, and the variant used in North America and a few other places is called u-law. They compress linear samples of 13 to 14 bits at 8ksps to samples of 8 bits at 8ksps. This causes significant distortion, but everything designed for the telephone network since the late 1950s has been specifically designed to operate reliably through these codecs, both used alone and in tandem.

From the 1980s some operators introduced ADPCM compression for their long distance links, which can handle slow modems, but not the fastest ones. More recently, VoIP has brought some very low bit rate codecs into the mix, which, as with cellular systems, mean all attempts to use standard modems fail. ISDN was supposed to bring the wideband G.722 codec to the telephone network in the late 1980s, but wideband voice didn't catch on until very recently with cellular and VoIP.
Psi:
i wonder if you could craft the signal so the audio compression algorithm couldn't compress it a huge amount.
And get extra bandwidth out of the system that way.

Probably not, but its an interesting thought experiment.
Siwastaja:

--- Quote from: Psi on October 30, 2019, 06:14:30 am ---i wonder if you could craft the signal so the audio compression algorithm couldn't compress it a huge amount.
And get extra bandwidth out of the system that way.

--- End quote ---

No, as shown by the earlier replies, GSM compression is a fixed rate (of 13 kbit/s).

You'll get the most bandwidth out of the system by carefully designing and optimizing the modulation scheme for the GSM compression.
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