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How to Build Voice Translation Application Using NVIDIA NeMo

Author: Mirdul Swarup

Last Updated: Mon, Oct 16, 2023
Machine Learning Vultr Cloud GPU

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Neural Modules (NeMo) is an open-source toolkit designed to handle conversational AI tasks. It's part of NVIDIA's GPU Cloud (NGC) catalog which consists of a centralized repository of tools, frameworks, and pre-trained models. These models speed up the development, deployment, and management of Artificial Intelligence and high-performance computing workloads. NGC GPU accelerated containers are also an essential part of the NGC catalog pre-configured with optimized software and libraries to take advantage of GPU resources for accelerated performance.

This article explains how to use the NeMo framework in a GPU-accelerated PyTorch container to perform Automatic Speech Recognition (ASR) and Text-to-Speech (TTS) tasks. You are to install and run the PyTorch container, then, use NeMo pre-trained models to convert imported French audio into English audio.


Before you begin:

Install PyTorch and Access Jupyter Notebook

To use the NeMo framework on a cloud GPU server, install and run the PyTorch GPU container with port binding using Docker. Then, access the Jupyter Notebook service pre-installed in the container as described in the steps below.

  1. Using Docker, install and run the PyTorch GPU container

    $ sudo docker run --gpus all -p 9000:8888 -it

    The above command runs the PyTorch GPU-accelerated docker container with the following configurations:

    • --gpus all: Allocates all available server GPUs to the Docker container. This ensures that all GPU resources run GPU-accelerated tasks

    • -p 9000:8888: Maps the host port 9000 on your server to the container port 8888. This creates a separate Jupyter Notebook access port different from the Vultr GPU Stack Jupyter Lab service that runs on port 8888

    • -it: Starts the container in interactive mode with access to its shell

    When successful, verify that your server prompt changes to the root container shell

  2. Start Jupyter Notebook as a background process

    # jupyter notebook --ip= &

    Your output should look like the one below:

        To access the notebook, open this file in a browser:
    Or copy and paste this URL:

    As displayed in the above output, copy the generated token ?token=XXXX to securely access Jupyter Notebook in your web browser.

  3. Using a web browser such as Chrome, access Jupyter Notebook on your public server IP on port 9000 using the generated access token


Article Flow

Run the Pre-Trained Models

To use pre-trained models and necessary NeMo functions, import the NeMo modules. Then, initialize the pre-trained models, and perform tasks like audio transcription and text-to-speech synthesis in a Jupyter Notebook session as described below.

  1. Access the Jupyter Notebook web interface

  2. In the middle right corner, click the New dropdown to reveal a dropdown list

    Create a new Jupyter Notebook

  3. Select Python 3 (ipykernel) under the Notebook: category to open a new file

  4. Within the new Jupyter Notebook file, add the following code in a new cell to install the necessary dependency packages

    !pip install Cython nemo_toolkit[all] hydra-core transformers sentencepiece webdataset youtokentome pyannote.metrics jiwer ijson sacremoses sacrebleu rouge_score einops unidic-lite mecab-python3 opencc pangu ipadic wandb nemo_text_processing pytorch-lightning

    Below is what each package represents:

    • Cython: A Python module that allows you to write C extensions for Python. It's often used for performance optimization

    • nemo_toolkit[all]: A framework for building conversational AI models. The [all] flag installs all available components and NeMo dependencies

    • hydra-core: A framework for configuring complex applications. It's used to manage configuration settings in a clean and organized way

    • transformers: Works with pre-trained models in Natural Language Processing (NLP), including models like BERT, GPT-2, among others

    • sentencepiece: A library that performs text tokenization and segmentation, often used in NLP tasks

    • webdataset: Performs efficient data loading and augmentation, it's particularly useful in deep learning workflows

    • youtokentome: A library that performs subword tokenization and useful for language modeling tasks

    • pyannote.metrics: A toolkit for speaker diarization and audio analysis tasks that contains evaluation metrics for these tasks

    • jiwer: A library for computing the Word Error Rate (WER), a common metric used in Automatic Speech Recognition (ASR) and other speech-processing tasks

    • ijson: A library for parsing large JSON documents incrementally. It's useful when efficiently working with large data files

    • sacremoses: A Python library that performs tokenization, de-tokenization, and various text-processing tasks

    • sacrebleu: Evaluates machine translation quality using the BLEU metric

    • rouge_score: A library for computing the ROUGE evaluation metric often used in text summarization and machine translation

    • einops: A library for tensor operations and reshaping useful when developing deep learning models

    • unidic-lite: A morphological analysis dictionary

    • mecab-python3: A tokenizer part-of-speech tagger that works in the Python binding for MeCab

    • opencc: A library for simplified and traditional Chinese text conversion

    • pangu: A Chinese text spacing library for adding spaces between Chinese characters

    • ipadic: A morphological analysis dictionary

    • wandb: Tracks and visualizes machine learning experiments

    • nemo_text_processing: Contains text processing utilities specific to the NVidia NeMo Toolkit

    • pytorch-lightning: A lightweight wrapper for PyTorch that simplifies training Deep Learning models

  5. Press Run on the main menu bar or press CTRL + ENTER to install the packages

  6. In a new code cell, import the necessary modules

    import nemo
    import nemo.collections.asr as nemo_asr
    import nemo.collections.nlp as nemo_nlp
    import nemo.collections.tts as nemo_tts
    import IPython

    The above commands import the necessary modules required to run the NeMo pre-trained models. Below is what each module represents:

    • nemo: Allows you to access NeMo's functionalities and classes

    • nemo.collections.asr: Allows you to access NeMo's ASR-related functionalities and models

    • nemo_nlp: Allows to use NeMo's NLP-related tools, models, and utilities

    • nemo_tts: Allows you to use NeMo's TTS-related functionalities and models

    • IPython: Allows you to interactively run and experiment with NeMo code interactively

  7. Open the NGC NeMo catalog


    The above command lists all available models in the following categories:

    • Automatic speech recognition

    • Encoder-decoder: A Natural Language Processing (NLP) collection part of the MTEnDec category

    • Text-to-speech: HifiGan and FastPitch

    Based on the catalog, use the following models:

    • stt_fr_quartznet15x5: For speech recognition, specific to the French language

    • nmt_fr_en_transformer12x2: Translates text from one language to another, specific to the French language

    • tts_en_fastpitch: Generates a spectrogram for text input to text-to-speech

    • tts_en_lj_hifigan_ft_mixertts: Converts spectrograms into speech for TTS

  8. Initialize the models

    asr_model = nemo_asr.models.EncDecCTCModel.from_pretrained(model_name='stt_fr_quartznet15x5').cuda()
    nmt_model = nemo_nlp.models.MTEncDecModel.from_pretrained(model_name='nmt_fr_en_transformer12x2').cuda()
    spectrogram_generator = nemo_tts.models.FastPitchModel.from_pretrained(model_name='tts_en_fastpitch').cuda()
    vocoder = nemo_tts.models.HifiGanModel.from_pretrained(model_name='tts_en_lj_hifigan_ft_mixertts').cuda()

    Wait for at least 15 minutes for the initialization process to complete successfully

Perform Audio Transcription and Synthesis

  1. Download a French audio sample. Replace the link with your desired audio source URL

    !wget ''
    audio_sample = 'bonjour.mp3'

    The above command downloads the public French MP3 sample audio file bonjour.mp3 and saves it in your Jupyter Notebook working directory. In addition, it uses IPython's Audio widget to display and play the audio file in your Jupyter Notebook session

  2. Transcribe the audio sample to text

    transcribed_text = asr_model.transcribe([audio_sample])

    The above command uses the speech recognition model and displays the transcribed text from the audio content


  3. Translate the text to English

    english_text = nmt_model.translate(transcribed_text)

    The above command uses the pre-trained model to convert the French text to English and displays the converted text


  4. Generate a Spectogram

    parseText = spectrogram_generator.parse(english_text[0])
    spectrogram = spectrogram_generator.generate_spectrogram(tokens=parseText)

    The above command converts the English text into a spectrogram, this is a preprocessing step in text-to-speech synthesis, the spectrogram represents the special characteristics of the generated audio

  5. Convert the spectrogram to audio

    audio = vocoder.convert_spectrogram_to_audio(spec=spectrogram)
    audioOutput ='cpu').detach().numpy()

    The above command processes the input text to a TTS pipeline to generate the audio output

  6. View the transcribed audio


    Verify that the generated transcribed audio matches your English text at a rate of 22050 Hz


You have built an AI Translator using the NeMo framework pre-trained models and the NGC GPU accelerated container on a Vultr Cloud GPU Server. You transcribed a French audio sample to French text, then, you converted the text to English text and transcribed the text to an English audio sample. Using NeMo modules and pre-trained models from the NGC catalog, the audio speech recognition pipeline becomes efficient and convenient to use.

More Information

For more information, visit the following documentation resources:

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