Another Formula I Stuck with

Note: this question has connection to my prev question : http://www.mathworks.com/matlabcentral/answers/65795-what-is-the-meaning-of-this-formula are the step 2 and i manage to get through it and step 3 too. But step 4 i don't understand how to read the formula

Step 3. Apply a two-level DWT to the left-channel of the stereo audio signal. The DWT operation produces the one-dimensional sub-bands shown below in Figure 1, where A2 is the approximation sub-band, and D1 and D2 are the first-level and second-level details sub-bands, respectively. Its important to note here that the decision was made to adopt the two-level DWT since it gave better results than higher DWT levels.

so here is step 4 and it's formula :

any advise how i supposed to read it?

Answer 1

[Sandhya]

I am doing this paper as my project and due to some problem in step 3 I am unable to proceed further. Please can u give me your assistance in solving out the step 3 of this paper.