1. A computer-implemented method for bio-medical signal segmentation using a hidden Markov model, the model comprising a plurality of states, the method comprising the steps of: specifying a minimum duration constraint d min for at least one of the states; for each state in the model with a specified minimum duration, replacing the state by a set of sub-states, with the total number of sub-states equal to the value of the minimum duration constraint d min ; connecting together the set of sub-states to form a left-right Markov chain, wherein the first d min −1 sub-states each have a self-transition probability of zero, a transition probability of one of transitioning to the state immediately to their right, and a transition probability of zero of transitioning to any other state in the model; and applying the model to data representing the biomedical signal to obtain information on the segmentation of the signal into the states.