This program uses steganography, which is the science of writing a hidden message which is undetectable and indecipherable to all except the intended recipient. In this case, the message is hidden inside an sound file. More specifically, message is hidden in the lower 8 bits (1 byte) of a 16-bit AIFF file. An AIFF file uses a sequence of numbers to represent sound waves. When the lower byte is replaced by a secret message, the resulting sound waves are almost indistinguishable from the original.

The length of the message may not exceed the number of 16-bit integers in the audio file. You can figure this maximum length by subtracting the length of the 54 (0x36) byte AIFF header from the length of the entire audio file and dividing by 2:

   Message_Length <= (Audio_File_Length - 54) / 2

The message is terminated by a NULL character (0x00), so the message itself cannot contain such a character. In order to share a message containing binary data (characters not representable in ASCII), you can first encode your message into hexadecimal.

The source file must be an AIFF audio file using 16-bit audio encoding. The encoded message will be LOST if you change the format to MP3 or anything other than AIFF 16-bit!

If you have a message you would like to encode, choose or record a sound you would like to hide the message inside. If the sound you wish to use is another format, like MP3 or WMA, you must convert it into AIFF 16-bit. SoundCoder does not do this for you, so use Quicktime or some other 3rd party software. In SoundCoder, select "New" from the "File" menu. Type or paste your message. Click the "Encode..." button. You will be prompted to choose the sound you prepared earlier, so locate it in your file system. You will then be asked where to save the encoded sound file. Now, place the encoded sound file somewhere your recipient can access it. Nobody will ever suspect that a secret message is hidden inside the sound file!

To decode the secret message, select "Decode..." from the "File" menu. You will be prompted for the encoded sound file. The hidden message will appear in a new window!