0. Questions/Concerns
1. Conserving AUs
2. Acoustic Modeling at 50k feet
    A. train a decision tree to "state-tie" certain triphones together
    B. train an HMM for each triphone where the transition probabilities are modeled by GMM (`pdf`)
        - typically 3-5 states
              - way of dealing with dipthongs?
    C. given a frame, find the most representative `pdf`
3. Three Acoustic Models
     A. Monophones
          - quality of model not important
          - poor alignment, but a "good start" that will be bootrapped
     B. Triphones
          - model context of triphones
          - require "state tying" because the number of triphones is too large
              - done by decision tree, asking "questions" about left and right context
     C. Triphones + LDA_MLLT
         - a transformation of the triphone model
              - for what purpose?
4. Highlights of `exp` dir
    A. the `mdl` file
5. Intuitions about acoustic modeling
    A. number of Gaussians
    B. number of leaves
5. Next week
    A. openFST: http://www.openfst.org/twiki/bin/view/FST/WebHome
    B. revisit our `ARPA` language model as an `FST`