» Code examples / Audio Data / Audio Classification with Hugging Face Transformers

Audio Classification with Hugging Face Transformers

Author: Sreyan Ghosh
Date created: 2022/07/01
Last modified: 2022/08/27
Description: Training Wav2Vec 2.0 using Hugging Face Transformers for Audio Classification.

View in Colab GitHub source


Identification of speech commands, also known as keyword spotting (KWS), is important from an engineering perspective for a wide range of applications, from indexing audio databases and indexing keywords, to running speech models locally on microcontrollers. Currently, many human-computer interfaces (HCI) like Google Assistant, Microsoft Cortana, Amazon Alexa, Apple Siri and others rely on keyword spotting. There is a significant amount of research in the field by all major companies, notably Google and Baidu.

In the past decade, deep learning has led to significant performance gains on this task. Though low-level audio features extracted from raw audio like MFCC or mel-filterbanks have been used for decades, the design of these low-level features are flawed by biases. Moreover, deep learning models trained on these low-level features can easily overfit to noise or signals irrelevant to the task. This makes it is essential for any system to learn speech representations that make high-level information, such as acoustic and linguistic content, including phonemes, words, semantic meanings, tone, speaker characteristics from speech signals available to solve the downstream task. Wav2Vec 2.0, which solves a self-supervised contratsive learning task to learn high-level speech reprentations, provides a great alternative to traditional low-level features for training deep learning models for KWS.

In this notebook, we train the Wav2Vec 2.0 (base) model, built on the Hugging Face Transformers library, in an end-to-end fashion on the keyword spotting task and achieve state-of-the-art results on the Google Speech Commands Dataset.


Installing the requirements

pip install git+https://github.com/huggingface/transformers.git
pip install datasets
pip install huggingface-hub
pip install joblib
pip install librosa

Importing the necessary libraries

import random
import logging

import numpy as np
import tensorflow as tf
from tensorflow import keras
from tensorflow.keras import layers

# Only log error messages
# Set random seed

Define certain variables

# Maximum duration of the input audio file we feed to our Wav2Vec 2.0 model.
# Sampling rate is the number of samples of audio recorded every second
BATCH_SIZE = 32  # Batch-size for training and evaluating our model.
NUM_CLASSES = 10  # Number of classes our dataset will have (11 in our case).
HIDDEN_DIM = 768  # Dimension of our model output (768 in case of Wav2Vec 2.0 - Base).
MAX_SEQ_LENGTH = MAX_DURATION * SAMPLING_RATE  # Maximum length of the input audio file.
# Wav2Vec 2.0 results in an output frequency with a stride of about 20ms.
MAX_EPOCHS = 2  # Maximum number of training epochs.

MODEL_CHECKPOINT = "facebook/wav2vec2-base"  # Name of pretrained model from Hugging Face Model Hub

Load the Google Speech Commands Dataset

We now download the Google Speech Commands V1 Dataset, a popular benchmark for training and evaluating deep learning models built for solving the KWS task. The dataset consists of a total of 60,973 audio files, each of 1 second duration, divided into ten classes of keywords ("Yes", "No", "Up", "Down", "Left", "Right", "On", "Off", "Stop", and "Go"), a class for silence, and an unknown class to include the false positive. We load the dataset from Hugging Face Datasets. This can be easily done with the load_dataset function.

from datasets import load_dataset

speech_commands_v1 = load_dataset("superb", "ks")

The dataset has the following fields:

  • file: the path to the raw .wav file of the audio
  • audio: the audio file sampled at 16kHz
  • label: label ID of the audio utterance
    train: Dataset({
        features: ['file', 'audio', 'label'],
        num_rows: 51094
    validation: Dataset({
        features: ['file', 'audio', 'label'],
        num_rows: 6798
    test: Dataset({
        features: ['file', 'audio', 'label'],
        num_rows: 3081

Data Pre-processing

For the sake of demonstrating the workflow, in this notebook we only take small stratified balanced splits (50%) of the train as our training and test sets. We can easily split the dataset using the train_test_split method which expects the split size and the name of the column relative to which you want to stratify.

Post splitting the dataset, we remove the unknown and silence classes and only focus on the ten main classes. The filter method does that easily for you.

Next we sample our train and test splits to a multiple of the BATCH_SIZE to facilitate smooth training and inference. You can achieve that using the select method which expects the indices of the samples you want to keep. Rest all are discarded.

speech_commands_v1 = speech_commands_v1["train"].train_test_split(
    train_size=0.5, test_size=0.5, stratify_by_column="label"

speech_commands_v1 = speech_commands_v1.filter(
    lambda x: x["label"]
    != (
        and speech_commands_v1["train"].features["label"].names.index("_silence_")

speech_commands_v1["train"] = speech_commands_v1["train"].select(
    [i for i in range((len(speech_commands_v1["train"]) // BATCH_SIZE) * BATCH_SIZE)]
speech_commands_v1["test"] = speech_commands_v1["test"].select(
    [i for i in range((len(speech_commands_v1["test"]) // BATCH_SIZE) * BATCH_SIZE)]

    train: Dataset({
        features: ['file', 'audio', 'label'],
        num_rows: 896
    test: Dataset({
        features: ['file', 'audio', 'label'],
        num_rows: 896

Additionally, you can check the actual labels corresponding to each label ID.

labels = speech_commands_v1["train"].features["label"].names
label2id, id2label = dict(), dict()
for i, label in enumerate(labels):
    label2id[label] = str(i)
    id2label[str(i)] = label

{'0': 'yes', '1': 'no', '2': 'up', '3': 'down', '4': 'left', '5': 'right', '6': 'on', '7': 'off', '8': 'stop', '9': 'go', '10': '_silence_', '11': '_unknown_'}

Before we can feed the audio utterance samples to our model, we need to pre-process them. This is done by a Hugging Face Transformers "Feature Extractor" which will (as the name indicates) re-sample your the inputs to sampling rate the the model expects (in-case they exist with a different sampling rate), as well as generate the other inputs that model requires.

To do all of this, we instantiate our Feature Extractor with the AutoFeatureExtractor.from_pretrained, which will ensure:

We get a Feature Extractor that corresponds to the model architecture we want to use. We download the config that was used when pretraining this specific checkpoint. This will be cached so it's not downloaded again the next time we run the cell.

The from_pretrained() method expects the name of a model from the Hugging Face Hub. This is exactly similar to MODEL_CHECKPOINT and we just pass that.

We write a simple function that helps us in the pre-processing that is compatible with Hugging Face Datasets. To summarize, our pre-processing function should:

  • Call the audio column to load and if necessary resample the audio file.
  • Check the sampling rate of the audio file matches the sampling rate of the audio data a model was pretrained with. You can find this information on the Wav2Vec 2.0 model card.
  • Set a maximum input length so longer inputs are batched without being truncated.
from transformers import AutoFeatureExtractor

feature_extractor = AutoFeatureExtractor.from_pretrained(
    MODEL_CHECKPOINT, return_attention_mask=True

def preprocess_function(examples):
    audio_arrays = [x["array"] for x in examples["audio"]]
    inputs = feature_extractor(
    return inputs

# This line with pre-process our speech_commands_v1 dataset. We also remove the "audio"
# and "file" columns as they will be of no use to us while training.
processed_speech_commands_v1 = speech_commands_v1.map(
    preprocess_function, remove_columns=["audio", "file"], batched=True

# Load the whole dataset splits as a dict of numpy arrays
train = processed_speech_commands_v1["train"].shuffle(seed=42).with_format("numpy")[:]
test = processed_speech_commands_v1["test"].shuffle(seed=42).with_format("numpy")[:]

Defining the Wav2Vec 2.0 with Classification-Head

We now define our model. To be precise, we define a Wav2Vec 2.0 model and add a Classification-Head on top to output a probability ditribution of all classes for each input audio sample. Since the model might get complex we first define the Wav2Vec 2.0 model with Classification-Head as a Keras layer and then build the model using that.

We instantiate our main Wav2Vec 2.0 model using the TFWav2Vec2Model class. This will instantiate a model which will output 768 or 1024 dimensional embeddings according to the config you choose (BASE or LARGE). The from_pretrained() additionally helps you load pre-trained weights from the Hugging Face Model Hub. It will download the pre-trained weights together with the config corresponding to the name of the model you have mentioned when calling the method. For our task, we choose the BASE variant of the model that has just been pre-trained, since we fine-tune over it.

from transformers import TFWav2Vec2Model

def mean_pool(hidden_states, feature_lengths):
    attenion_mask = tf.sequence_mask(
        feature_lengths, maxlen=MAX_FRAMES, dtype=tf.dtypes.int64
    padding_mask = tf.cast(
        tf.reverse(tf.cumsum(tf.reverse(attenion_mask, [-1]), -1), [-1]),
    hidden_states = tf.where(
            tf.expand_dims(~padding_mask, -1), (BATCH_SIZE, MAX_FRAMES, HIDDEN_DIM)
    pooled_state = tf.math.reduce_sum(hidden_states, axis=1) / tf.reshape(
        tf.math.reduce_sum(tf.cast(padding_mask, dtype=tf.dtypes.float32), axis=1),
        [-1, 1],
    return pooled_state

class TFWav2Vec2ForAudioClassification(layers.Layer):
    """Combines the encoder and decoder into an end-to-end model for training."""

    def __init__(self, model_checkpoint, num_classes):
        super(TFWav2Vec2ForAudioClassification, self).__init__()
        # Instantiate the Wav2Vec 2.0 model without the Classification-Head
        self.wav2vec2 = TFWav2Vec2Model.from_pretrained(
            model_checkpoint, apply_spec_augment=False, from_pt=True
        self.pooling = layers.GlobalAveragePooling1D()
        # Drop-out layer before the final Classification-Head
        self.intermediate_layer_dropout = layers.Dropout(0.5)
        # Classification-Head
        self.final_layer = layers.Dense(num_classes, activation="softmax")

    def call(self, inputs):
        # We take only the first output in the returned dictionary corresponding to the
        # output of the last layer of Wav2vec 2.0
        hidden_states = self.wav2vec2(inputs["input_values"])[0]

        # If attention mask does exist then mean-pool only un-masked output frames
        if tf.is_tensor(inputs["attention_mask"]):
            # Get the length of each audio input by summing up the attention_mask
            # (attention_mask = (BATCH_SIZE x MAX_SEQ_LENGTH) ∈ {1,0})
            audio_lengths = tf.cumsum(inputs["attention_mask"], -1)[:, -1]
            # Get the number of Wav2Vec 2.0 output frames for each corresponding audio input
            # length
            feature_lengths = self.wav2vec2.wav2vec2._get_feat_extract_output_lengths(
            pooled_state = mean_pool(hidden_states, feature_lengths)
        # If attention mask does not exist then mean-pool only all output frames
            pooled_state = self.pooling(hidden_states)

        intermediate_state = self.intermediate_layer_dropout(pooled_state)
        final_state = self.final_layer(intermediate_state)

        return final_state

Building and Compiling the model

We now build and compile our model. We use the SparseCategoricalCrossentropy to train our model since it is a classification task. Following much of literature we evaluate our model on the accuracy metric.

def build_model():
    # Model's input
    inputs = {
        "input_values": tf.keras.Input(shape=(MAX_SEQ_LENGTH,), dtype="float32"),
        "attention_mask": tf.keras.Input(shape=(MAX_SEQ_LENGTH,), dtype="int32"),
    # Instantiate the Wav2Vec 2.0 model with Classification-Head using the desired
    # pre-trained checkpoint
    wav2vec2_model = TFWav2Vec2ForAudioClassification(MODEL_CHECKPOINT, NUM_CLASSES)(
    # Model
    model = tf.keras.Model(inputs, wav2vec2_model)
    # Loss
    loss = tf.keras.losses.SparseCategoricalCrossentropy(from_logits=False)
    # Optimizer
    optimizer = keras.optimizers.Adam(learning_rate=1e-5)
    # Compile and return
    model.compile(loss=loss, optimizer=optimizer, metrics=["accuracy"])
    return model

model = build_model()

Training the model

Before we start training our model, we divide the inputs into its dependent and independent variables.

# Remove targets from training dictionaries
train_x = {x: y for x, y in train.items() if x != "label"}
test_x = {x: y for x, y in test.items() if x != "label"}

And now we can finally start training our model.

    validation_data=(test_x, test["label"]),
Epoch 1/2
28/28 [==============================] - 25s 338ms/step - loss: 2.3122 - accuracy: 0.1205 - val_loss: 2.2023 - val_accuracy: 0.2176
Epoch 2/2
28/28 [==============================] - 5s 189ms/step - loss: 2.0533 - accuracy: 0.2868 - val_loss: 1.8177 - val_accuracy: 0.5089

<keras.callbacks.History at 0x7fcee542dc50>

Great! Now that we have trained our model, we predict the classes for audio samples in the test set using the model.predict() method! We see the model predictions are not that great as it has been trained on a very small number of samples for just 1 epoch. For best results, we reccomend training on the complete dataset for at least 5 epochs!

preds = model.predict(test_x)
28/28 [==============================] - 4s 44ms/step

Now we try to infer the model we trained on a randomly sampled audio file. We hear the audio file and then also see how well our model was able to predict!

import IPython.display as ipd

rand_int = random.randint(0, len(test_x))

ipd.Audio(data=np.asarray(test_x["input_values"][rand_int]), autoplay=True, rate=16000)

print("Original Label is ", id2label[str(test["label"][rand_int])])
print("Predicted Label is ", id2label[str(np.argmax((preds[rand_int])))])
Original Label is  up
Predicted Label is  on

Now you can push this model to Hugging Face Model Hub and also share it with with all your friends, family, favorite pets: they can all load it with the identifier "your-username/the-name-you-picked", for instance:

model.push_to_hub("wav2vec2-ks", organization="keras-io")
tokenizer.push_to_hub("wav2vec2-ks", organization="keras-io")

And after you push your model this is how you can load it in the future!

from transformers import TFWav2Vec2Model

model = TFWav2Vec2Model.from_pretrained("your-username/my-awesome-model", from_pt=True)