Hi see
wavedec() in the Wavelet Toolbox. You need to be careful about what you call the db4 wavelet. If that is the number of taps, then that is the 'db2' wavelet in the Wavelet Toolbox.
An example of the DWT down to level 4 using the 'db2' wavelet.
x = randn(1024,1);
C,L] = wavedec(x,4,'db2');