Introduction: Secret Message in Audio

Picture of Secret Message in Audio

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:

Picture of
  • 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:

Picture of

  • 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:

Picture of

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.


RezLar (author)2015-04-30

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?

ShakeTheFuture (author)RezLar2015-04-30

At what point did you fail?

What exactly did not work?

RezLar (author)ShakeTheFuture2015-04-30

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

ShakeTheFuture (author)RezLar2015-05-01

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.

RezLar (author)ShakeTheFuture2015-05-06

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

ShakeTheFuture (author)RezLar2015-05-07

That's great!

Thanks for letting us know.

JavaJack (author)2014-11-10

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

tinyweasel (author)JavaJack2014-12-30

That's what I was thinking. I was so impressed with Richard D. James doing this.

odiekokee made it! (author)2014-11-06

Very nice. I can see this coming handy combined with HAM

ShakeTheFuture (author)odiekokee2014-11-10

Very cool!

Raphango (author)2014-11-05

Whoa! Very cool! =D

ShakeTheFuture (author)Raphango2014-11-05

I am glad you like it.


Alderin (author)2014-11-05

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!

ShakeTheFuture (author)Alderin2014-11-05

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.

The Lightning Stalker (author)2014-11-05

You did not provide links to any of this software.

Yes, I assumed it's not hard to find it. I guess it's always a good idea to include links.


Yes it is. Coagula was slightly difficult to find.

Good -ible, thanks

Beergnome (author)2014-11-04

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.

ShakeTheFuture (author)Beergnome2014-11-05

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.

DIY-Guy (author)2014-11-04

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!

snoopindaweb (author)2014-11-04

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

ekasnaktsoglou (author)2014-11-04

A M A Z I N G !!!

R_H made it! (author)2014-11-03

That's pretty cool. I just ran Coagula in Wine under Linux then used Audacity and it worked fine. But then I thought I'd try my iPad instead of the tape and used a free app ( Spectro Real but I am sure it's not the only one ) to record audio played through speakers. I think this has some educational value, could be a neat little experiment :)

ShakeTheFuture (author)R_H2014-11-03

Great information. Thanks for sharing.

sur1c4t4 (author)2014-11-03

This is the steganography.

You can hide message into picture, audio, video.

More info to

swaxman (author)2014-11-02

Very very impressive - robot worthy

ShakeTheFuture (author)swaxman2014-11-02

Thank you Swaxman.

gomiboy (author)2014-11-01

This is used by ham radio operators, and was even used by NASA to transmit "slow-scan television" in the early days of space exploration. Very cool way to do it! Nicely done.

ugur23 (author)gomiboy2014-11-02

i tried it weeks ago. i could record 256×256 picture in 96sec . (RGB)

and with mfsk , i could record text to tape directly (no pictures etc. just like to serial terminal)

that is very nice and cool ! .

ShakeTheFuture (author)gomiboy2014-11-02

Wow, cool. I did not know that. Cheers

asteadman (author)2014-10-31


ShakeTheFuture (author)asteadman2014-10-31


rimar2000 (author)2014-10-30

¡Very interesting!

Another easy way –not hacker proof– is to change the extension of the file. It is to say:

– If the message is in txt, doc, odt or another text format, you can change the format to avi, mp3, asf, etc.

– If the message is in jpg, bmp or another image format, you can change the format to txt, doc, odt, etc.

PipeChela (author)rimar20002014-10-31

and then minimize the windows so you speed up your internet.

ShakeTheFuture (author)rimar20002014-10-31

Yes, that's another option indeed. Old school, but still effective :)

Qwertyfish (author)2014-10-30

Pretty cool


tomatoskins (author)2014-10-30

I would have never thought of using and audio signal to send text. I love it!

Cheers. It's definetly fun, at least if you are a child or a spy :)

torchbearer (author)2014-10-30

very cool,well done!!!

Thank You!

About This Instructable




Bio: Innovative Projects, Diy's, Life Hacks
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