Speech Recognition using DeepSpeech2 and the CTC activation function. Edit
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Implementation of DeepSpeech2 using Baidu Warp-CTC. Creates a network based on the DeepSpeech2 architecture, trained with the CTC activation function.


  • Train DeepSpeech, configurable RNN types and architectures with multi-gpu support.
  • Language model support using kenlm (WIP right now, currently no instructions to build a LM yet).
  • Multiple dataset downloaders, support for AN4, TED, Voxforge and Librispeech. Datasets can be merged, support for custom datasets included.
  • Noise injection for online training to improve noise robustness.
  • Audio augmentation to improve noise robustness.
  • Easy start/stop capabilities in the event of crash or hard stop during training.
  • Visdom/Tensorboard support for visualising training graphs.


Several libraries are needed to be installed for training to work. I will assume that everything is being installed in an Anaconda installation on Ubuntu.

Install PyTorch if you haven't already.

Install this fork for Warp-CTC bindings:

git clone https://github.com/SeanNaren/warp-ctc.git
cd warp-ctc
mkdir build; cd build
cmake ..
export CUDA_HOME="/usr/local/cuda"
cd ../pytorch_binding
python setup.py install

Install pytorch audio:

sudo apt-get install sox libsox-dev libsox-fmt-all
git clone https://github.com/pytorch/audio.git
cd audio
pip install cffi
python setup.py install

If you want decoding to support beam search with an optional language model, install ctcdecode:

git clone --recursive https://github.com/parlance/ctcdecode.git
cd ctcdecode
pip install .

Finally clone this repo and run this within the repo:

pip install -r requirements.txt



Currently supports AN4, TEDLIUM, Voxforge and LibriSpeech. Scripts will setup the dataset and create manifest files used in dataloading.


To download and setup the an4 dataset run below command in the root folder of the repo:

cd data; python an4.py


You have the option to download the raw dataset file manually or through the script (which will cache it). The file is found here.

To download and setup the TEDLIUM_V2 dataset run below command in the root folder of the repo:

cd data; python ted.py # Optionally if you have downloaded the raw dataset file, pass --tar_path /path/to/TEDLIUM_release2.tar.gz


To download and setup the Voxforge dataset run the below command in the root folder of the repo:

cd data; python voxforge.py

Note that this dataset does not come with a validation dataset or test dataset.


To download and setup the LibriSpeech dataset run the below command in the root folder of the repo:

cd data; python librispeech.py

You have the option to download the raw dataset files manually or through the script (which will cache them as well). In order to do this you must create the following folder structure and put the corresponding tar files that you download from here.

cd data/
mkdir LibriSpeech/ # This can be anything as long as you specify the directory path as --target_dir when running the librispeech.py script
mkdir LibriSpeech/val/
mkdir LibriSpeech/test/
mkdir LibriSpeech/train/

Now put the tar.gz files in the correct folders. They will now be used in the data pre-processing for librispeech and be removed after formatting the dataset.

Optionally you can specify the exact librispeech files you want if you don't want to add all of them. This can be done like below:

cd data/
python librispeech.py --files_to_use "train-clean-100.tar.gz, train-clean-360.tar.gz,train-other-500.tar.gz, dev-clean.tar.gz,dev-other.tar.gz, test-clean.tar.gz,test-other.tar.gz"

Custom Dataset

To create a custom dataset you must create a CSV file containing the locations of the training data. This has to be in the format of:


The first path is to the audio file, and the second path is to a text file containing the transcript on one line. This can then be used as stated below.

Merging multiple manifest files

To create bigger manifest files (to train/test on multiple datasets at once) we can merge manifest files together like below from a directory containing all the manifests you want to merge. You can also prune short and long clips out of the new manifest.

cd data/
python merge_manifests.py --output_path merged_manifest.csv --merge_dir all_manifests/ --min_duration 1 --max_duration 15 # durations in seconds


python train.py --train_manifest data/train_manifest.csv --val_manifest data/val_manifest.csv

Use python train.py --help for more parameters and options.

There is also Visdom support to visualise training. Once a server has been started, to use:

python train.py --visdom

There is also Tensorboard support to visualise training. Follow the instructions to set up. To use:

python train.py --tensorboard --logdir log_dir/ # Make sure the tensorboard instance is made pointing to this log directory

For both visualisation tools, you can add your own name to the run by changing the --id parameter when training.

Noise Augmentation/Injection

There is support for two different types of noise; noise augmentation and noise injection.

Noise Augmentation

Applies small changes to the tempo and gain when loading audio to increase robustness. To use, use the --augment flag when training.

Noise Injection

Dynamically adds noise into the training data to increase robustness. To use, first fill a directory up with all the noise files you want to sample from. The dataloader will randomly pick samples from this directory.

To enable noise injection, use the --noise_dir /path/to/noise/dir/ to specify where your noise files are. There are a few noise parameters to tweak, such as --noise_prob to determine the probability that noise is added, and the --noise_min, --noise_max parameters to determine the minimum and maximum noise to add in training.

Included is a script to inject noise into an audio file to hear what different noise levels/files would sound like. Useful for curating the noise dataset.

python noise_inject.py --input_path /path/to/input.wav --noise_path /path/to/noise.wav --output_path /path/to/input_injected.wav --noise_level 0.5 # higher levels means more noise


Training supports saving checkpoints of the model to continue training from should an error occur or early termination. To enable epoch checkpoints use:

python train.py --checkpoint

To enable checkpoints every N batches through the epoch as well as epoch saving:

python train.py --checkpoint --checkpoint_per_batch N # N is the number of batches to wait till saving a checkpoint at this batch.

Note for the batch checkpointing system to work, you cannot change the batch size when loading a checkpointed model from it's original training run.

To continue from a checkpointed model that has been saved:

python train.py --continue_from models/deepspeech_checkpoint_epoch_N_iter_N.pth.tar

This continues from the same training state as well as recreates the visdom graph to continue from if enabled.

If you would like to start from a previous checkpoint model but not continue training, add the --finetune flag to restart training from the --continue_from weights.

Choosing batch sizes

Included is a script that can be used to benchmark whether training can occur on your hardware, and the limits on the size of the model/batch sizes you can use. To use:

python benchmark.py --batch_size 32

Use the flag --help to see other parameters that can be used with the script.

Model details

Saved models contain the metadata of their training process. To see the metadata run the below command:

python model.py --model_path models/deepspeech.pth.tar

To also note, there is no final softmax layer on the model as when trained, warp-ctc does this softmax internally. This will have to also be implemented in complex decoders if anything is built on top of the model, so take this into consideration!


To evaluate a trained model on a test set (has to be in the same format as the training set):

python test.py --model_path models/deepspeech.pth.tar --test_manifest /path/to/test_manifest.csv --cuda

An example script to output a transcription has been provided:

python transcribe.py --model_path models/deepspeech.pth.tar --audio_path /path/to/audio.wav

Alternate Decoders

By default, test.py and transcribe.py use a GreedyDecoder which picks the highest-likelihood output label at each timestep. Repeated and blank symbols are then filtered to give the final output.

A beam search decoder can optionally be used with the installation of the ctcdecode library as described in the Installation section. The test and transcribe scripts have a --decoder argument. To use the beam decoder, add --decoder beam. The beam decoder enables additional decoding parameters:

  • beam_width how many beams to consider at each timestep
  • lm_path optional binary KenLM language model to use for decoding
  • alpha weight for language model
  • beta bonus weight for words

Time offsets

Use the --offsets flag to get positional information of each character in the transcription when using transcribe.py script. The offsets are based on the size of the output tensor, which you need to convert into a format required. For example, based on default parameters you could multiply the offsets by a scalar (duration of file in seconds / size of output) to get the offsets in seconds.

Pre-trained models

Pre-trained models can be found under releases here.


Thanks to Egor and Ryan for their contributions!