TensorFlow Speech Recognition Challenge

This repo contains my part of the code for our winning entry in the TensorFlow Speech Recognition Challenge hosted by kaggle. The task was to build an algorithm that understands simple speech commands. Our team (team name: Heng-Ryan-See * good bug? *) won the competition with a private leaderboard score of: 0.91060.

Members

• Heng Cher Keng
• Ryan Sun
• Steffen Eberbach

Summary of my approach

I started with the provided tutorial and could easily get better results by just adding momentum to the plain SGD solver. I have no prior experience with audio data and mostly used deep learning with images. For this domain you don't use features but feed the raw pixel values. My thinking was that this should also work with audio data. During the competition, I ran experiments using raw waveforms, spectrograms and log mel features as input. I got similar results using log mel and raw waveform (86%-87%) and used the waveform data for most experiments as it was easier to interpret.

For the special price the restrictions were: the network is smaller than 5.000.000 bytes and runs in less than 175ms per sample on a stock Raspberry Pi 3. Regarding the size, this allows you to build networks that have roughly 1.250.000 weight parameters. So by experimenting with these restrictions I came up with an architecture that uses Depthwise1D convolutions on the raw waveform. Using model distillation this network predicts the correct class for 90.8% of the private leaderboard samples and runs in roughly 60ms. Training the model takes ~4 hours using a Google Cloud instance with K80 GPU.

What didn't work

• Fancy augmentation methods: I tried flipping (i.e: * -1.0) the samples. You can check that they will sound exactly the same. I also modified input_data.py to change the foreground and background volume independently and created a separate volume range for the silence samples. My validation accuracy improved for some experiments but my leaderboard scores didn't.

• Predicting unknown unknowns: I didn't find a good way to consistently predict these words. Often, similar words were wrongly classified (e.g. one as on).

• Creating new words: I trained some networks with even more classes. I reversed the samples from the known unwanted words, e.g. bird, bed, marvin, and created new classes (bird -> drib ...). The idea was to have more unknowns to prevent the network from wrongly mapping unknowns to the known words. For example the word follow was mostly predicted as off. However, neither my validation score not my leaderboard score improved.

• Cyclic learning rate schedules: The winning entry of the Caravana Image Masking Challenge used cyclic learning rates but for me the results got worse and you had additional hyperparameters. Maybe I just didn't implement it correctly.

What worked

• Mixing TensorFlow and Keras: Both frameworks work perfectly together and you can mix them wherever you want. For example: I wrapped the provided data AudioProcessor from input_data.py in a generator and used it with keras.models.Model.fit_generator. This way, I could implement new architectures really fast using Keras and later just extract and freeze the graph from the trained models (see freeze_graph.py).

• Pseudo labeling: I used consistent samples from the test set to train new networks. Choosing them was based on a.) my three best models agree on this submission. I used this version at early stages of the competition. b.) using a probability threshold on the predicted softmax probabilities. Typically, using pseudo_threshold=0.6 were the samples that our ensembled model predicted correctly. I also implemented a schedule for pseudo labels. That is: For the first 5 epochs you only use pseudo labels and then gradually mix in data from the training data set. Though, I didn't have time to run these experiments, so I kept a fixed ratio of training and pseudo data.

• Test time augmentation (TTA): It is a simple way to get some boost. Just augment the samples, feed them multiple times and average the probabilities. I tried the following: time-shifting, increase/decrease the volume and time-stretching using librosa.effects.time_stretch.

Appendix

A1.) Model Execution Time

• What software did you use for training and prediction?
  • see Requirements
• What hardware (CPUS spec, number of CPU cores, memory)?
  • a single GCP instance with 4 vCPUs, 18.5 GB memory and 1 x NVIDIA Tesla K80
• How long does it take to train your model?
  • ~4-8 hours (depends on the model) for a single model
• How long does it take to generate predictions using your model?
  • ~4 minutes without TTA, on the Pi 3 (make_submission_on_rpi.py) it takes ~134 minutes

A2.) Requirements:

• tensorflow-gpu==1.4.0
• Keras==2.1.2 (the version that comes with TensorFlow 2.0.8-tf should be fine as well but you'll need to adjust the imports)
• tqdm==4.11.2
• scipy==1.0.0
• numpy==1.13.3
• pandas==0.20.3
• pandas-ml==0.5.0

All packages can be installed via pip3 install. Other versions will probably work too. I tested it with Python 3.5.2 using Ubuntu 16.04.

Pi requirements:

• GNU/Linux 8 (Jessie): http://downloads.raspberrypi.org/raspbian/images/raspbian-2017-07-05
• to run the benchmark script only TensorFlow is required. I installed it using this tutorial: https://petewarden.com/2017/08/20/cross-compiling-tensorflow-for-the-raspberry-pi and used the Python 3.4 part:

sudo apt-get install libblas-dev liblapack-dev python-dev \
 libatlas-base-dev gfortran python-setuptools
sudo ​pip install \
 http://ci.tensorflow.org/view/Nightly/job/nightly-pi-python3/lastSuccessfulBuild/artifact/output-artifacts/tensorflow-1.4.0-cp34-none-any.whl

To create the whole submission file (make_submission_on_rpi.py) you'll need these additional packages (pip3 install and I got a HTTPError which can be solved by using the --default-timeout=100 flag):

• pandas==0.22.0
• tqdm==4.19.5
• scipy==1.0.0 (sudo pip3 install --default-timeout=100 --no-deps scipy)

Note that installing scipy will take a couple hours. I tried removing this dependency by using the wave and struct modules but then reading the wavs is super slow (2 hours for all test files). I tested it with Raspbian GNU/Linux 8 (Jessie) and Python 3.4.2.

A3.) How To Generate the Solution

Structure

This repo contains all the code (.py or .ipynb) to reproduce my part of our submission. You'll find various model definitions in model.py, the training script is train.py and the scripts to make the submissions are make_submission.py (faster as it processes samples in batches) or make_submission_on_rpi.py (suitable to create the submission file on the Pi 3: frozen graph, batch size of 1 and fewer dependecies). Keras models checkpoints can be found in checkpoints_*, TensorBoard training logs in logs_* and frozen TensorFlow graphs in tf_files. I am providing these files for the experiments that are required for the final submission. Though, I ran many more. As a result each section of this writeup can be executed independently. The data is assumed to be in data/train and data/test:

mkdir data
ln -s your/path/to/train data/train
ln -s your/path/to/test data/test

Model training

Only the predicted probabilites by the model from experiment 106 made it to our final ensemble submission. I trained a lot more but this one was the best. This model is trained with pseudo labels and additional noise. So the first step is to reproduce these samples:

git checkout 6892d80
git checkout master REPR_106_pseudo.py submission_091_leftloud_tta_all_labels.csv submission_096_leftloud_tta_all_labels.csv submission_098_leftloud_tta_all_labels.csv
python3 generate_noise.py
python3 REPR_106_pseudo.py

And then train the model:

mkdir checkpoints_106
python3 train.py

For the submission, I selected the checkpoint with the highest validation accuracy using TensorBoard:

tensorboard --logdir logs_106

The reference model is checkpoints_106/ep-062-vl-0.1815.hdf5.

Note that due to stochasticity (random initialization, data augmentation and me not setting a seed) exactly reproducing these weights is probably not possible.

Make the submission using TTA:

git checkout master make_submission.py
git checkout master checkpoints_106/ep-062-vl-0.1815.hdf5  # change line 64 of `make_submission.py` instead of this command if you use another checkpoint
python3 make_submission.py

The resulting submission (REPR_submission_106_tta_leftloud.csv) will have a public/private score of 0.88558/0.88349. Every sample is used three times (unchanged, shifted to the left by 1500 timesteps and made louder by multiplying with 1.2). The resulting probabilities are then averaged. Note that this model uses 32 classes. These probabilities will be stored in REPR_submission_106_tta_leftloud_all_labels_probs.csv. In order to use them for the ensembled model the order of the samples and the probabilities have to be converted to 12 classes:

git checkout master convert_from_see_v3_bugfix.py
python3 convert_from_see_v3_bugfix.py

This will create the file: submission_106_tta_leftloud_all_labels_probs.uint8.memmap for our ensemble model.

Raspberry Pi model

This model is trained with pseudo labels from our best ensembled submission: submission_50.csv/submit_50_probs.uint8.memmap. To train this model, first reproduce the pseudo labels using this submission and then run the training script:

git checkout ad2af0d
git checkout master create_pseudo_with_thresh.py submission_50.csv submit_50_probs.uint8.memmap
python3 create_pseudo_with_thresh.py
mkdir checkpoints_195
python3 train.py

For this training I am only saving the checkpoints with the best validation accuracy. Therefore, there is no need to inspect the logs. Just use the latest checkpoint.

To freeze the model run:

git checkout master freeze_graph.py
git checkout master checkpoints_195/ep-085-vl-0.2231.hdf5  # skip this if you trained the model yourself
python3 freeze_graph.py --checkpoint_path checkpoints_195/ep-085-vl-0.2231.hdf5 --frozen_path tf_files/frozen_195.pb

You can then reproduce the best scoring Raspberry Pi submission rpi_submission_195.csv by running:

# on the pi
git checkout master
python3 make_submission_on_rpi.py --frozen_graph tf_files/frozen_195.pb --test_data data/test/audio --submission_fn rpi_submission_195.csv

This submission will have a score of 0.89747/0.90825 on the public/private leaderboard.

Benchmarking the Pi model

You can benchmark the frozen graph using the provided benchmark binary:

curl -O https://storage.googleapis.com/download.tensorflow.org/deps/pi/2017_10_07/benchmark_model
chmod +x benchmark_model
./benchmark_model --graph=tf_files/frozen_195.pb --input_layer="decoded_sample_data:0,decoded_sample_data:1" --input_layer_shape="16000,1:" --input_layer_type="float,int32" --input_layer_values=":16000" --output_layer="labels_softmax:0" --show_run_order=false --show_time=false --show_memory=false --show_summary=true --show_flops=true

I got the following results:

• avg time (ms): 58.042
• max memory (bytes): 2180436
• size (bytes): 4870144 (du -s -B1 tf_files/frozen_195.pb)