I am working on isolated word recognition using HMMsand have a few basic questions on HMMs. 1. I have to recognize digits using HMMs. Hence, it is an Isolated Word Recognition. 2. Say the digits are 1-7. I am having 1 class per digit i.e., 5 utterances per class.. How many HMMs will I be obtaining? Will it be 1 per utterance (i.e., 5 per class) or 1 per class (1 per digit)? 3. What should be the input to these HMMs. How will I relate my signals (training signals) to the HMMs? 4. I have extracted features for each signal. They are Mel-Cepstrum Coefficients. I have been told that these features would be the input to the HMMs but in vector notation. So, I applied VQ to these features. Now, I have 1 sequence of vectors per signal. i.e., 7*55 sequences in all. 5. How will I train my HMM with these sequences? The method I used is as follows: 6. I have assumed the transition probabilities and the initial probability to build a random HMM. Later I will update the probabilities with correct values. 7. According to Rabiners paper: www.ai.mit.edu/~murphyk/Bayes/rabiner.pdf , once I build a model by assuming the initial probabilities, I have to extract an observation sequence with the model built. Why should a new observation sequence be extracted when I have all training sequences ready (by extracting features)?? 8. I have not found the new sequence with the model prepared. I continued with 1 sequence among the 35. Applied FB method, Viterbi method and found the most likely state sequence for the i/p observation sequence I considered. 9. I tried to update the model parameters by re-estimating the values, but couldnt do it successfully. Am trying to use the Baum-Welch method. 10. Say it is done, should I find the ML state sequence for all the sequences ( in the same class ) using the updated model?? I am assuming that Ill have 1 model per word. 11. Again, once the training part is done, for the testing part, Ill take a sample sequence, and find the ML state sequence using the updated model parameters. Is it right? Or should I find another model for the testing sequence as well , find the ML state sequence and compare the two models?? 12. What probabilities should be compared or what parameters of the HMMs should be compared to perform the recognition??? Please reply at the earliest. I am out of time. regards, Ash. __________________________________ |

# HMM

Started by ●June 9, 2004