基于Torchaudio构建数据集

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前言

本系列本来打算每一章都写笔记记录下来，不过看来几个视频之后，发现2，3其只是在普及torch以及复现基础手写字体识别的例子，与torchaudio和音频处理关系不大，就跳过，感兴趣的可以直接看代码。4，5，6，7都是在讲解如何构建数据集，所以一并记录：

02 Training a feed forward network

构建和训练mnist手写字符识别网络

03 Making predictions

推理接口的实现

04 Creating a custom dataset

创建数据集处理类

05 Extracting Mel spectrograms

基于torchaudio提取音频的梅尔频谱特征

06 Padding audio files

样本的Padding和cut

07 Preprocessing data on GPU

使用GPU训练

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一、下载数据集

官方数据集要注册才能下载，直接从这里urbansound8k下载。

文件目录

其中audio是音频文件，大概8700多个
metadata为标注的文件夹

标注格式

metadata/UrbanSound8K.csv:

二、UrbanSoundDataset类的定义

class UrbanSoundDataset(Dataset):

    def __init__(self, annotations_file, audio_dir):
        self.annotations = pd.read_csv(annotations_file)
        # 使用panda加载csv
        self.audio_dir = audio_dir

    def __len__(self):
        return len(self.annotations)

    def __getitem__(self, index):
        audio_sample_path = self._get_audio_sample_path(index)
        label = self._get_audio_sample_label(index)
        signal, sr = torchaudio.load(audio_sample_path)
        # 返回tensor类型的音频序列和采样率，与librosa.load的区别是，librosa返回的音频序列是numpy格式
        return signal, label

    def _get_audio_sample_path(self, index):
        fold = f"fold{self.annotations.iloc[index, 5]}"
        path = os.path.join(self.audio_dir, fold, self.annotations.iloc[
            index, 0])
        return path

    def _get_audio_sample_label(self, index):
        return self.annotations.iloc[index, 6]

三、提取梅尔频谱特征

梅尔频谱为音频信号处理中常见的特征表示，torchaudio中使用torchaudio.transforms模块来实现

定义梅尔转换

mel_spectrogram = torchaudio.transforms.MelSpectrogram(
        sample_rate=SAMPLE_RATE,
        n_fft=1024,
        hop_length=512,
        n_mels=64
    )

修改UrbanSoundDataset类，初始化时传入：

class UrbanSoundDataset(Dataset):
    def __init__(self, annotations_file, audio_dir, transformation,
                 target_sample_rate):
        self.annotations = pd.read_csv(annotations_file)
        self.audio_dir = audio_dir
        self.transformation = transformation
        self.target_sample_rate = target_sample_rate

重采样

在梅尔转换之前，需要对音频信号进行重采样和多声道合并，所以定义这两个函数：

    def _resample_if_necessary(self, signal, sr):
        # 每个信号的采样率不一致，如果跟共有变量的采样率不一致的话，需要重采样
        if sr != self.target_sample_rate:
            resampler = torchaudio.transforms.Resample(sr, self.target_sample_rate)
            signal = resampler(signal)
        return signal

多声道合并

    def _mix_down_if_necessary(self, signal):
        # 每个signal -> (channel,samples) -> (2,16000) -> (1,16000)
        # 需要把所有的通道混合起来，保持维度不变
        if signal.shape[0] > 1:
            signal = torch.mean(signal, dim=0, keepdim=True)
        return signal

完善get_item

然后在get_item的函数里把几个函数串起来，则完成了梅尔频谱特征提取的过程：

    def __getitem__(self, index):
        audio_sample_path = self._get_audio_sample_path(index)
        label = self._get_audio_sample_label(index)
        signal, sr = torchaudio.load(audio_sample_path)
        signal = self._resample_if_necessary(signal, sr) # 重采样
        signal = self._mix_down_if_necessary(signal) # 多声道合并
        signal = self.transformation(signal) # 梅尔频谱提取
        return signal, label

五、样本padding和cut

由于训练的要求，需要把每个信号样本都缩放到同一尺度，所以使用了padding（尺度小于阈值），cut(尺度大于阈值)的处理，添加两个函数：

cut的实现

直接取前面到阈值的部分（似乎有点简单粗暴？）

    def _cut_if_necessary(self, signal):
        # 举例 signal -> Tensor -> (1,num_samples) -> (1,50000) -> 切片后变成 (1,22500)
        if signal.shape[1] > self.num_samples:
            signal = signal[:, :self.num_samples]
        return signal

pad实现，右边补0

    def _right_pad_if_necessary(self, signal):
        length_signal = signal.shape[1]
        if length_signal < self.num_samples:
            num_missing_samples = self.num_samples - length_signal
            last_dim_padding = (0, num_missing_samples)
            # 每个signal都是二维的，所以以上式子，第一个0是不pad的，只pad第二维
            signal = torch.nn.functional.pad(signal, last_dim_padding)
        return signal

五、GPU支持

就是加了一个判断，这也单独列了一章……

    if torch.cuda.is_available():
        device = "cuda"
    else:
        device = "cpu"
    print(f"Using device {device}")

六、完整代码

import os

import torch
from torch.utils.data import Dataset
import pandas as pd
import torchaudio


class UrbanSoundDataset(Dataset):

    def __init__(self,
                 annotations_file,
                 audio_dir,
                 transformation,
                 target_sample_rate,
                 num_samples,
                 device):
        self.annotations = pd.read_csv(annotations_file)
        self.audio_dir = audio_dir
        self.device = device
        self.transformation = transformation.to(self.device)
        self.target_sample_rate = target_sample_rate
        self.num_samples = num_samples

    def __len__(self):
        return len(self.annotations)

    def __getitem__(self, index):
        audio_sample_path = self._get_audio_sample_path(index)
        label = self._get_audio_sample_label(index)
        signal, sr = torchaudio.load(audio_sample_path)
        signal = signal.to(self.device)
        signal = self._resample_if_necessary(signal, sr)
        signal = self._mix_down_if_necessary(signal)
        signal = self._cut_if_necessary(signal)
        signal = self._right_pad_if_necessary(signal)
        signal = self.transformation(signal)
        return signal, label

    def _cut_if_necessary(self, signal):
        if signal.shape[1] > self.num_samples:
            signal = signal[:, :self.num_samples]
        return signal

    def _right_pad_if_necessary(self, signal):
        length_signal = signal.shape[1]
        if length_signal < self.num_samples:
            num_missing_samples = self.num_samples - length_signal
            last_dim_padding = (0, num_missing_samples)
            signal = torch.nn.functional.pad(signal, last_dim_padding)
        return signal

    def _resample_if_necessary(self, signal, sr):
        if sr != self.target_sample_rate:
            resampler = torchaudio.transforms.Resample(sr, self.target_sample_rate)
            signal = resampler(signal)
        return signal

    def _mix_down_if_necessary(self, signal):
        if signal.shape[0] > 1:
            signal = torch.mean(signal, dim=0, keepdim=True)
        return signal

    def _get_audio_sample_path(self, index):
        fold = f"fold{self.annotations.iloc[index, 5]}"
        path = os.path.join(self.audio_dir, fold, self.annotations.iloc[
            index, 0])
        return path

    def _get_audio_sample_label(self, index):
        return self.annotations.iloc[index, 6]


if __name__ == "__main__":
    ANNOTATIONS_FILE = "/home/valerio/datasets/UrbanSound8K/metadata/UrbanSound8K.csv"
    AUDIO_DIR = "/home/valerio/datasets/UrbanSound8K/audio"
    SAMPLE_RATE = 22050
    NUM_SAMPLES = 22050

    if torch.cuda.is_available():
        device = "cuda"
    else:
        device = "cpu"
    print(f"Using device {device}")

    mel_spectrogram = torchaudio.transforms.MelSpectrogram(
        sample_rate=SAMPLE_RATE,
        n_fft=1024,
        hop_length=512,
        n_mels=64
    )

    usd = UrbanSoundDataset(ANNOTATIONS_FILE,
                            AUDIO_DIR,
                            mel_spectrogram,
                            SAMPLE_RATE,
                            NUM_SAMPLES,
                            device)
    print(f"There are {len(usd)} samples in the dataset.")
    signal, label = usd[0]

总结

以上就是整个数据集的定义、加载、预处理及梅尔频谱特征提取过程，为后续的训练做好数据的准备。