Spectrogram

In this example, we will use the Coagula software and Audacity software, but it is possible to use other software’s that offer the same manipulation.

• Download and install Coagula and Audacity on your computer.
• Open the Coagula software.
• It is possible to import images into Coagula, but they will have to be simple and use few colours to give a correct result. You can also draw directly in the software. Draw or import your message or secret code.
• In the menu bar, select Sound, then Render Without Blue.
• Save your file with File > Save Sound As…. The default settings of the software are sufficient to obtain a good conversion. You will obtain a WAV file.
• Open the Audacity software.
• Import the file created with Coagula into Audacity.
• Display the spectrogram of the track.
• In the menu bar, select Effects > Amplify and reduce the intensity of the sound to make it almost inaudible.
• Import the other file to be used as a vector or save your message directly in Audacity.
• Select the different parts of the code separately and copy and paste them into the vector track.
• Delete the coded message track (the spectogram) and export your file.
• Be careful! Mixing corresponds to an integration of the code in the vector message. Do not merge the two tracks, as this could erase the spectrogram code.