Sonorant

This is a language model for English words, but using sounds (phonemes) rather than letters. It's an RNN trained in PyTorch on words from the CMU Pronouncing Dictionary, a corpus of phonemic transcriptions of words. Each word is a sequence of International Phonetic Alphabet symbols. So for example the word "fish" is /ˈfɪʃ/ and the word "cough" is /ˈkɑːt/.

There are a few places you might want to look:

• Run the interactive app, or visit it at sonorant.io. It lets you construct new words one phoneme at a time by iteratively choosing the next phoneme from a distribution.
• The Jupyter notebook Model Training.ipynb to see how the language model over phonemes was trained.
• The Jupyter notebook Model Exploration and Usage.ipynb to a trained model. I cover (a) what are the most- and least-Englishy words, (b) generating novel words, and (c) probing the model to see whether it really learned English phonotactics.
• The Python module sonorant/languagemodel.py contains the actual PyTorch language model. It has some nice helper methods and is well tested. See the section Language Model below for more on how to use it.

If you want to run these examples follow the instructions in the Setup section below.

Setup

1. Create and source a virtualenv. python3 -m venv .venv && source .venv/bin/activate
2. Upgrade pip. pip install --upgrade pip
3. Install dependencies. pip install -r requirements/development.txt
4. Set environment variables for AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY, for an AWS user that has access to AmazonPollyReadOnlyAccess. Note that this will result in billable usage of AWS Polly, even when just running unit tests since I haven't mocked it out.
5. Run tests to make sure everything is working. make test

To run the interactive app:

1. Start the Flask server. make runserver
2. Navigate to localhost:5000

To see the notebooks:

1. Start Jupyter notebook server. jupyter notebook --port=8888
2. You can now navigate to localhost:8888/tree in your browser. Open Model Training.ipynb or Model Exploration and Usage.ipynb.

Language Model

The majority of code in this repo isn't specific to pronunciations. sonorant/languagemodel.py contains a class LanguageModel, which is a neural language model that can be trained on any type of texts. In this section I'll outline its functionalities.

Import these three classes.

>>> from sonorant.languagemodel import LanguageModel, ModelParams, Vocabulary

Define the train and dev texts. Build a Vocabulary from the texts, which handles the mapping of tokens like "a" to integer indices.

>>> train_texts = [("a", "cat", "ate"), ("some", "dogs", "slept")]
>>> dev_texts = [("some", "cat", "ate"), ("dogs", "slept")]
>>> vocab = Vocabulary.from_texts(train_texts + dev_texts)
>>> len(vocab)
Out[1]: 9
>>> vocab['a']
Out[2]: 3

Define ModelParams, which encapsulate the hyperparameters for a model. This is a useful abstraction that allows parameters to be passed around as a group rather than one by one and aids serialization.

>>> model_params = ModelParams(
    rnn_type="gru",
    embedding_dimension=50,
    hidden_dimension=30,
    num_layers=1,
    max_epochs=2,
    early_stopping_rounds=5,
)

A model is defined by a vocabulary, model parameters, and the name of the device on which it'll run. Any Torch devices will work, but you probably want "cuda" if you're running on a GPU and "cpu" otherwise.

>>> model = LanguageModel(vocab, model_params, device_name="cpu")

To train a model pass a sequence of train texts and dev texts to the fit function. At the end of every epoch the model prints out the loss for the dev set. Note that max_epochs and a few other parameters set in model_params can be overriddedn by passing them to fit.

>>> train_errors, dev_errors = model.fit(train_texts, dev_texts, max_epochs=10)

Now I'll run through some basic operations over a trained model.

You can calculate the perplexity of any text. Perplexity is basically the length normalized, inverse probability. length normalized.

>>> model.perplexity_of_text(dev_texts[0])
Out[3]: 14.466998156671036

You can pass in a tuple of tokens and the model will return a probability distribution over the vocabulary for its predictions of which token will come next.

>>> model.next_probabilities(("a", "cat"))
Out[4]:
{'<PAD>': 0.0008051212062127888,
 '<START>': 0.004382132086902857,
 '<END>': 0.010958804748952389,
 'a': 0.00777098536491394,
 'cat': 0.005946762394160032,
 'ate': 0.944864809513092,
 'some': 0.00814706552773714,
 'dogs': 0.0017555770464241505,
 'slept': 0.015368768945336342}

You can generate novel texts.

>>> model.generate(max_length=1000)
Out[5]: ('dogs', 'cat')

You can save the model to disk and then load it.

>>> with open('model.pt', 'wb') as fh:
    model.save(fh)

>>> with open('model.pt', 'rb') as fh:
    the_same_model = LanguageModel.load(fh, device_name='cpu')

Related Work

• https://github.com/aparrish/pronouncingpy
• https://github.com/Kyubyong/g2p
• https://pytorch.org/tutorials/intermediate/seq2seq_translation_tutorial.html
• https://www.stonybrook.edu/commcms/amp2019/_pdf/_Poster2/2.13Nelson.pdf