Notes

The decoder will analyse sound coming from the microphone or from an audio file. The spectrogram of the sound is shown in the main graph along with a pink region showing the frequency being analysed. If the volume in the chosen frequency is louder than the "Volume threshold" then it is treated as being part of a dit or dah, and otherwise it records a gap (this is shown in the lower graph that looks like a barcode). From these timings it determines if something is a dit, dah, or a sort of space and then converts it into a letter shown in the message box.

In fully automatic mode, the decoder selects the loudest frequency and adjusts the Morse code speed to fit the data. If you want to fix the frequency or speed then click on the "Manual" checkboxes and type in your chosen values. The frequency can only be certain values and the closest allowed value will be chosen.

There are three parameters which are not automatic: the minimum and maximum volume filter settings and the volume threshold setting. The volume filter (which uses dB) discards very quiet (very negative) or very loud (close to zero) sounds and scales the size of the remaining data. The volume threshold is the value (0-255) which the measured volume in the analysed frequency must exceed to be counted as a dit or dah.

If you've read this far, you may be interested in the older version of this tool which does not attempt to adapt to the sound and also includes more diagnostic information.