Consider the analysis-synthesis filter bank shown in Figure 6.1 with input signal, $s(n)$. Show that $\hat{s}(n)=\frac{1}{M} \sum_{m=-\infty}^{\infty} \sum_{l=-\infty}^{\infty} \sum_{k=0}^{M-1} s(m)$ $h_k(l M-m) g_k(l-M n)$, where $M$ is the number of subbands.