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I have a number of uncompressed audio files recorded off of an analog (POTS) telephone line of fax transmissions. Is there a Linux utility or library I could use to convert these files into images of the fax they contain? I'm not looking to send/receive a fax via a modem, but just to "replay" the communications tones and parse out the fax message.I'm guessing this may not be possible due to duplex issues and not knowing which end of the conversation is sending what,but thought I'd ask to see if anyone knew of something.

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4 Answers

Most faxes from the past decade are CCITT Group 3 or 4, containing image/g3fax or image/g4fax data which is encapsulated, or rather modulated, in one of V.27, V.29, V.17, V.34, or V.34bis.

Note that the fax transmission is not so-much a transmission, as a 2-way communication. Thus, you cannot simply play this audio back into a fax machine and expect it to work. However, luckily, the fax image data transmission itself is uninterrupted, so it is possible to filter out the unnecessary data.

What you will need to do is demodulate the content to retrieve the binary fax session and to filter out and extract the image/g3fax or image/g4fax data.

The late Tony Fischer wrote a software fax demodulator for V.34. It only works on Irix, so you'll need to port it. There was a Linux port at some time, but I couldn't find any valid links. http://www-users.cs.york.ac.uk/~fisher/software/modem/current/

There is also the Linmodem project.

Between these resources and some C programming, you should be able to extract the faxes... this isn't for the faint of heart, but possible, if the data is that important to you.

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The recordings you have probably contain enough information to reassemble the information. However I do not know of any off-the-shelf way to do this in linux or any other operating system.

You might like to look at the soft modems or the amateur radio software modems - you might be able to play it back through a loopback or something.

Alternatively - look at the standards and implement it yourself. Better warm up your DSP programming skills. :)

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I dont know about using a program to do that, but you could always play the sound through your modem to a fax machine and print them out that way. assuming it plays correctly, you wouldnt need to worry about the two machines playing nice and getting an error because the bits that were identifiers wouldnt be heard by your machine while its transmitting. but this is all speculation to the highest degree.

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Building on what Jasen said, you could set up your linux box to accept faxes, and then play that sound over the lines going to the computer. If your recording involves the ring tones sent over, it should work.

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