Currently, I'm working on my project about audio steganography using discrete wavelet transform (dwt). I'm using matlab to code and implement the system.

My goal is to successfully embed a text (*.txt) file used as message to be hidden in an audio file (*.wav).

I have no problem to make the system work by using single level dwt because in matlab there are built-in dwt and idwt function that can be used to decompose and reconstruct an one dimensional signal.

My problem is I can't do the multi-level dwt decomposition and reconstruction of a 1-D signal.

Well, there really are built-in function in matlab to do this, i.e. wavedec and waverec. But I can't use it straight away.

In my case, I need to access and modify the last level approximation coefficient or detail coefficient, and reconstruct the signal with this modified coefficient. Meanwhile, waverec will reconstruct signal using the coefficient produced by wavedec function *I suppose*. That will return in the original signal with no modified coefficient.

If anyone can help me, it'll be great.

Thank you before.