BA_quant

  This fuction performs backward adaptive quantisation of the input vector x It returns the quantised signal yb, the quantised index ind for each sample of yb and the quantiser step size ss used for each sample of yb The algorithm commences with the step size set according to a non adaptive unfirom quantiser(This fuction performs backward adaptive quantisation of the input vector x It returns the quantised signal yb, the quantised index ind for each sample of yb and the quantiser step size ss used for each sample of yb The algorithm commences with the step size set according to a non adaptive unfirom quantiser)