LEAF: a LEarnable Audio Frontend

LEAF is a learnable alternative to audio features such as mel-filterbanks, that can be initialized as an approximation of mel-filterbanks, and then be trained for the task at hand, while using a very small number of parameters.

A complete description of the system is available in our recent ICLR publication.

Dependencies

• Python 3.8
• TensorFlow
• TensorFlow Datasets
• Gin
• Lingvo

Contents

This library contains Tensorflow/Keras code for:

• the LEAF frontend, as well as mel-filterbanks, SincNet and Time-Domain Filterbanks
• Keras models for PANN, PCEN and SpecAugment
• an example training loop using gin, to train models with various frontends and architectures on tensorflow datasets.

Installation

From the root directory of the repo, run:

pip3 install -e .

Creating a Leaf frontend

We provide learnable and fixed frontends as Keras Models. Instantiating Leaf with default arguments will build a LEAF frontend with a 25ms window size, a 10ms window stride, sPCEN as compression function and an initialization of filters on the mel-scale, as described in the paper. For convenience, we also propose Time-Domain Filterbanks, SincNet and SincNet+ as particular instantations of Leaf, with different layers and initializers.

import leaf_audio.frontend as frontend

leaf = frontend.Leaf()
melfbanks = frontend.MelFilterbanks()
tfbanks = frontend.TimeDomainFilterbanks()
sincnet = frontend.SincNet()
sincnet_plus = frontend.SincNetPlus()

A frontend takes a batch of waveform sequences as inputs, and outputs a batch of time-frequency representations.

import tensorflow as tf
import tensorflow_datasets as tfds

dataset = iter(tfds.load('speech_commands', split='train', shuffle_files=True))
# Audio is in int16, we rescale it to [-1; 1].
audio_sample = next(dataset)['audio'] / tf.int16.max
# The frontend expects inputs of shape [B, T] or [B, T, C].
audio_sample = audio_sample[tf.newaxis, :]

leaf_representation = leaf(audio_sample)
melfbanks_representation = melfbanks(audio_sample)
tfbanks_representation = tfbanks(audio_sample)
sincnet_representation = sincnet(audio_sample)
sincnet_plus_representation = sincnet_plus(audio_sample)

Customizing the frontend architecture

One can easily build new frontends from LEAF, by changing the number of filters, window_size, compression function, sampling rate and so on. In this case, one should instantiate Leaf with custom arguments. As an example, the following custom_leaf frontend differs from the default LEAF by using:

• 64 filters instead of 40,
• a window size of 32ms instead of 25,
• an audio sampling rate of 24kHz,
• a learnable pre-emphasis layer,
• log-compression instead of PCEN,
• a non-learnable pooling layer.

As the initialization depends on the sampling rate, we also need to redefine complex_conv_init.

import functools
from leaf_audio import frontend, initializers

n_filters = 64
window_len = 32
sample_rate = 24000
preemp = True
compression_fn = functools.partial(frontend.log_compression, log_offset=1e-5)
complex_conv_init = initializers.GaborInit(sample_rate=sample_rate, min_freq=60., max_freq=7800.)
learn_pooling=False
custom_leaf = frontend.Leaf(learn_pooling=learn_pooling,
                            n_filters=n_filters,
                            window_len=window_len,
                            sample_rate=sample_rate,
                            preemp=preemp,
                            compression_fn=compression_fn,
                            complex_conv_init=complex_conv_init)

Training audio classification models

We also provide a basic training library that allows combining a frontend with a main classification architecture (including PANN), and training it on a classification dataset.

This library uses Gin: common.gin contains the common hyperparameters such as the batch size or the classification architecture. Each frontend then has its own .gin config file that uses all hyperparameters from common.gin and overrides the frontend class. In leaf_custom.gin we show how Gin allows to easily change hyperparameters of the frontend, as well as the main classification architecture and using SpecAugment.

To train a model on mel-filterbanks:

python3 -m example.main --gin_config=example/configs/mel.gin

or on LEAF:

python3 -m example.main --gin_config=example/configs/leaf.gin

Reference

If you use this repository, please consider citing:

@article{zeghidour2021leaf,
  title={LEAF: A Learnable Frontend for Audio Classification},
  author={Zeghidour, Neil and Teboul, Olivier and de Chaumont Quitry, F{\'e}lix and Tagliasacchi, Marco},
  journal={ICLR},
  year={2021}
}

Note that this is not an officially supported Google product.