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I tried to use both:

But neither one worked. Can you recommend a tool or an alternative approach to decode a Morse message saved as an Mp3 file?

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    $\begingroup$ Did we try to listen and copy the CW manually? Not an answer, but the "old fashioned way" is always available. $\endgroup$ – Ron J. KD2EQS Jan 27 '14 at 13:48
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    $\begingroup$ How did they "not work"? It's a safe assumption that those programs do indeed "work", and you are using them incorrectly. Without a description of what really went wrong it's impossible to guess how. $\endgroup$ – Phil Frost - W8II Jan 27 '14 at 14:44
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    $\begingroup$ @RonJ.KD2EQS I'd argue that is an answer. The question doesn't specify that the "tool" or "alternative approach" can't involve wetware. $\endgroup$ – Phil Frost - W8II Jan 27 '14 at 15:03
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    $\begingroup$ I had good results using FLDIGI, but be aware that a certain amount of technical knowledge (configuring the program's levels and sensitivity and gain and signal thresholds) is required for ANY CW copying software to work at all. First play with a known signal, one you generated yourself. Figure out how to set your gains and your levels correctly. Then proceed to unknown signals. $\endgroup$ – Warren VE3WPX May 17 '15 at 1:07
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    $\begingroup$ Here is where you can get good prectice recordings for testing: W1AW Code Practice MP3 Files arrl.org/code-practice-files $\endgroup$ – SDsolar May 30 '18 at 19:39
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I'm not aware of a tool which will take an MP3 file as an input for CW decoding. You should be able to set up either of the software you tried to use a line in, and connect your computer speaker to the line in jack, then play the mp3 using another program while running either of the above decoders. There are ways to loop the sound through in software, but running a simple cable is easy to do and explain, so try that first.

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  • $\begingroup$ well, this tool claims to be able to convert an audio Morse file to text. Can anyone confirm! it is a python script. $\endgroup$ – MedAli Jan 27 '14 at 18:06
  • $\begingroup$ @MohamedAliJamaoui Which tool claims that? Neither of the tools you mentioned above appear to be python or accept a sound file. A link might help, particularly a link to the webpage that has this claim. $\endgroup$ – Adam Davis Jan 27 '14 at 18:09
  • $\begingroup$ sorry I forgot to include the link, here is it: code.google.com/p/morse-to-text/source/browse/#svn%2Ftrunk $\endgroup$ – MedAli Jan 27 '14 at 18:13
  • $\begingroup$ @MohamedAliJamaoui That software requires a WAV file format, not MP3. There are a lot of utilities out there to convert mp3 to wav. Once you've done that and installed python, you should be able to try the software out to decode your mp3. $\endgroup$ – Adam Davis Jan 27 '14 at 18:16
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    $\begingroup$ That sounds like a good question for dsp.stackexchange.com. $\endgroup$ – Adam Davis Jan 27 '14 at 18:27
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Can you recommend a tool or an alternative approach to decode a Morse message saved as an Mp3 file?

The old fashioned alternative approach is always available, using your ears.

The advantage of having a recorded (MP3) CW QSO is that you can pause, rewind, listen again. Print a chart of Morse code, listen, transcribe. You may even learn Morse in the process, and be able to listen to "live" CW.

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If you have an Apple Mac personal computer running a recent version of OS X, you can play the mp3 files using iTunes, or even the Safari web browser, out any built-in or external speaker, and run the HotPaw Morse Decoder app, available as a commercial product from the Mac App Store. If the volume is turned up enough, the background noise and recorded QRM are low enough, and the Morse Code is stable and well formed enough, the Morse Decoder app should be able to decode it into text.

Disclaimer: The Mac Morse Decoder app is a commercial product that I developed. An iOS version is also available. I used the above method, with mp3 recordings of actual over-the-air CW QSOs, to do regression testing and QA of the app. Hopefully that allows this answer to be suitably on-topic.

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  • $\begingroup$ Generally speaking, mentioning your own products in an answer is acceptable as long as the product in question actually helps the question author with their problem, such mentions are only a small number of your answers, and the answers that do mention your products clearly state your affiliation with the product. It seems to me in this case all these criteria are met, so you're fine. If you're concerned about a specific case, you can always ask over on Amateur Radio Meta before posting. $\endgroup$ – user Feb 4 '14 at 15:05
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If you are using Windows you could probably use the commercial CW Skimmer software in combination with a so called 'virtual audio cable'. A free (as in beer) virtual audio cable driver is VB-Cable. This installs as a virtual audio card in your system, which should make it possible to redirect the output of your MP3 player to CW Skimmer.

Of course, as suggested above, you could also use a physical cable to loop the signal from the output of your soundcard back into the computer. There are two drawbacks with this method though:

  1. You will probably need a second soundcard.
  2. The signal to noise ratio (SNR) will worsen slightly, since the analog connection outside of your computer will add noise. The D/A and A/D converters on the sound cards will add noise too.

Item number 2 above will not likely be a problem, unless you are listening to very weak morse signals. A shielded loop cable (made as short as possible) can be beneficial, but the noise from the A/D and D/A converters can only be remedied by use of a better (and likely more expensive) soundcard.

What SNR you need is ultimately determined by the decoder in CW Skimmer and the 'quality' and signalling speed of the received morse code.

Unfortunately I don't know of any open source software to solve your needs.

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  • $\begingroup$ A alternative, commercial virtual audio cable is called VAC. $\endgroup$ – SM6XMA Jan 28 '14 at 17:08
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You can download many free applications to convert a digital sound of morse or any other digital mode into text. My favorite is the last free version before it was sold, of Ham Radio Deluxe, and use the Digital Master 780 application inside the main program.

Install it, open DM-780 and set the Program Options to read the sound from almost any source your soundcard can hear, such as Line In to get the sound from the MP3 file. You can also open a window to one of the SDR websites, tune the digital radio in to a good frequency with CW or one of the digital modes come in and then set the Program Options to read from Line In, and decode to your hearts content.

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I have used an app called Morse Code Reader.

It works well for me!

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