Generating posteriors

The unit per frame posterior can be generated by running:

utils/phone_loop_fb_post.sh setup.sh parallel_opts keys_file model_in_dir output_dir

The posteriors are computed by running the forward-backward algorithm on the phone-loop model. The posteriors are stored in HTK binary format. Eventually, one can output the per state posteriors by using the options --hmm_states:

utils/phone_loop_fb_post.sh --hmm_states setup.sh parallel_opts keys_file model_in_dir output_dir

when using the --hmm_states options the output posterior dimension will be total number of units times the number of HMM states per unit. For example if we have a model with the truncation set to 100 and 3 states per unit-HMM the posteriors dimension will 100 x 3 = 300.

Naturally the posteriors tend to be very sharp, assigning all the probability mass to one or two dimensions. To prevent this behavior one can decrease the acoustic scaling in the setup file to a number smaller than one:

post_ac_weight=0.1

In a nutshell, when post_ac_weight is greater than or equal to 1, the posteriors will be very sharp whereas when it is set to values between 0 and 1 the posteriors will be smoother.