i am working in audio coding..what r the tools in matlab or in simulink to implement quadrature mirror filterbank??[/color]

Uh, two band or many band?

I mean, either is not very, um, difficult, really.

2 band for now...but i need many bad implementation also....

For the 2-channel case:

'lp' and 'hp' are the QMF low-/highpass filter fair (impulse response). Usually only the lowpass filter coeffs are given. You can derive the highpass filter coeffs by alternating the signs a la hp = lp .* ((-1).^(1:length(lp)));
'x' = original signal

"analysis":
xlo = upfirdn(x,lp,1,2);
xhi = upfirdn(x,hp,1,2);

"snythesis":
x2 = 2 * (upfirdn(xlo,lp,2,1) + upfirdn(xhi,-hp,2,1));

Note1: '-hp' = hp(length(hp):-1:1) = synthesis filter in the special case for 2-channel QMF filters.
Note2: You may need to remove some elements of 'x2' at the start and the end so it matches x.


HTH,
SG

Another way. Do all the even points in the convolution. Do all the odd separately. The sum is the low band, the difference is the high band. Ditto but exactly reversed on the other end.