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:
- 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.
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.
Below is the spectrum plot for "secret" audio message generated using Audacity.
Below image shows linear spectral chart for "secret" signal mixed with generated tone of 19kHz.
The below spectral graph is for the carrier "music" file.