What I want to do:
I want to encode an audio message inside a regular music file; this shall be decoded by an audio analyzer running on another machine (by listening to the audio playback from the first machine).
What I have tried so far:
Encode:
- Change the pitch of secret audio message to D#/EB-10 (which is 19.5 KHz according to this site: http://www.flutopedia.com/pitch_to_frequency.htm). This should convert the secret audio message to something that falls outside of the human audible range.
- Merge this secret audio message with music file.
Decode:
Apply high pass filter at 19 KHz.
Change pitch back to the original range (e.g. B-6)
I'm using Audacity to do the above steps.
The problems that I'm facing:
1. The "secret" message is still audible in the encoded output.
2. Decoded output is significantly different than the secret message.
I'm new to the audio dsp domain, so I'd appreciate a review of my approach and suggestions to achieve the goal that I described above.
Edit:
Below is the spectrum plot for "secret" audio message generated using Audacity.
Edit2:
Below image shows linear spectral chart for "secret" signal mixed with generated tone of 19kHz.
Edit3:
The below spectral graph is for the carrier "music" file.