Secret Message in Audio




About: Innovative Projects, Diy's, Life Hacks

Did you ever want to send a secret to message to your friend?

Here is a fun way to do it. You can hide a secret text message in audio file, tape, CD or anywhere you can hear it.

When audio is played, it will not make any sense.

It will sound similar to Dial Up modem or similar to sound when trying to load a game into "ZX-Spectrum" computer.

Message can be hidden in:

  • Any digital file (mp3, wav, wma, avi, mp4 etc.)
  • Youtube, vimeo etc.
  • Cassette, CD, vinyl etc.
  • It can be transferred via radio, walky talky etc.
  • Basicly as long as you can hear it and record it, you can decode it.

What do we need?

  • Some kind of image editor, like "Paint" or "Photoshop"
  • A free program called "Coagula"
  • A free program called "Audacity"

Step 1:

  • Create a new file in your chosen picture editor.
  • Set the pictures size to something like: 500x300 Pixels

Does not have to be exactly that size, that's what I used in this example

  • Set background to black
  • Write your secret message at the TOP of the picture

It's important to write it at the top, otherwise result might not be great.
It's better to use big and easy readable fonts.

  • Save your picture as a "bmp" file.

Step 2:

  • Import your "bmp" file into "Coagula"
  • Click on a button that looks like a cogwheel.

That will render your image to "wav" file

  • Save your "wav" file

That's it. You have successfully hidden the message in audio file.

Now you can upload it to Youtube, send it via e-mail or record it to audio cassette.

Or you can just play it loudly, so your neighbour or a friend can record it with mobile phone or a audio recorder.

Best result will be achieved using a digital file.

Step 3:

To decode the message, you will need to use "Audacity"

  • Import your audio file into "Audacity"
  • Click on a little arrow next to the files name and choose "Spectogram"

Now you should see your message.

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38 Discussions

Introducing Rosies

Tip 4 months ago

Note 1 - indead stuff being placed at the bottom of the image tends to get squeezed. Its because sound is represented in a logarithmic way. The upper side of the image is higher frequencies and the lower side is lower frequencies. Higher frequencies gives more "details" to the image if I may say so. If you have a sound editor you can increase the pitch value of the rendered sound as it will keep the "main shape" in higher frequencies... If you can switch off logarithmic scale on your spectrogram I guess the image will not get squeezed.
Note 2 - If you wanna play with whole pictures, take note 1 in consideration and also try to increase the contrast of the original image if you dont get enough details afterwards.
Note 3 - With Coagula, for both text and pictures always select the render image without blue/noise options (its the green and red cogwheel icon), this improved details.


3 years ago on Introduction

I cant seem to get it to work... I have my message and then I followed your steps exactly but cant seem to get it. Any ideas?

5 replies

Reply 3 years ago on Introduction

t was the end when you viewed the WAV as a spectrogram. Mine was red blobs. Since I know what I wrote I can kinda make it out but it looks nothing like yours


Reply 3 years ago on Introduction

Try to stretch the waveform.

(Last picture, where it says instructables)

Click on the border and try to stretch it or click on the side and try to scroll.


Reply 3 years ago on Introduction

I got it. Turns out the white on black does not work. If you change the font to red then it will work.


4 years ago on Introduction

Cool. Reminds me of the old Aphex Twin track ( He probably didn't have something as convenient as Coagula, though :)

1 reply

4 years ago on Introduction

Very cool! I wonder if using different positioning and different sized/shaped fonts would give less ... ear catching sounds. Then messages could be mixed into electronica or dubstep for added hiding factor.

Of course, if it is really secret, this should only be one layer of the whole package. :-)

Thanks for posting!

1 reply

Reply 4 years ago on Introduction

I guess it will make a difference in sound, but it will still sound annoying :)

Mixing in music is a good idea. I am sure with a lot of trial it's possible to get a sound that's not too annoying.


4 years ago on Introduction

In the before times, in the long, long ago, before floppies, this is how we stored data for future use for such computing platforms like the early atari and commodore series home computers. even my old Omnibots store programs as audio files on regular audio cassettes.

if you want to get even more obscure, program your message in Atari basic and allow it only to be transalted as an audio file run through an Atari turbo charger via a real console on a Television.

1 reply

That's great.

I remember my brother loading games and programs into ZX-Spectrum's clone computer. I have good memories. I remember he even had adult games. I guess they have been around since the first computer. Here is a nice video of somebody loading RoboCop into Zx-Spectrum.


4 years ago on Introduction

Has anybody checked Coagula 1.666 for malware yet?
There was an old Doom game v .666 that was just one big trojan malware product.

Otherwise this looks like a fun practice in steganography!


4 years ago on Introduction

A bit over My head, but thank You I may need it "for a friend". ~~~(:-})={> --- ]