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Scientific Audio Processing, Part I - How to read and write Audio files with Octave 4.0.0 on Ubuntu
================
Octave, the equivalent software to Matlab in Linux, has a number of functions and commands that allow the acquisition, recording, playback and digital processing of audio signals for entertainment applications, research, medical, or any other science areas. In this tutorial, we will use Octave V4.0.0 in Ubuntu and will start reading from audio files through writing and playing signals to emulate sounds used in a wide range of activities.
Note that the main focus of this tutorial is not to install or learn to use an audio processing software already established, but rather to understand how it works from the point of view of design and audio engineering.
### Prerequisites
The first step is to install octave. Run the following commands in a terminal to add the Octave PPA in Ubuntu and install the software.
```
sudo apt-add-repository ppa:octave/stable
sudo apt-get update
sudo apt-get install octave
```
### Step 1: Opening Octave.
In this step we open the software by clicking on its icon, we can change the work directory by clicking on the File Browser dropdown.
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/initial.png)
### Step 2: Audio Info
The command "audioinfo" shows us relevant information about the audio file that we will process.
```
>> info = audioinfo ('testing.ogg')
```
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/audioinfo.png)
### Step 3: Reading an audio File
In this tutorial I will read and use ogg files for which it is feasible to read characteristics like sampling , audio type (stereo or mono), number of channels, etc. I should mention that for purposes of this tutorial, all the commands used will be executed in the terminal window of Octave. First, we have to save the ogg file in a variable. Note: it´s important that the file must be in the work path of Octave
```
>> file='yourfile.ogg'
```
```
>> [M, fs] = audioread(file)
```
Where M is a matrix of one or two columns, depending on the number of channels and fs is the sampling frequency.
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/reading.png)
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/matrix.png)
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/big/frequency.png)
There are some options that we can use for reading audio files, such as:
```
>> [y, fs] = audioread (filename, samples)
>> [y, fs] = audioread (filename, datatype)
>> [y, fs] = audioread (filename, samples, datatype)
```
Where samples specifies starting and ending frames and datatype specifies the data type to return. We can assign values to any variable:
```
>> samples = [1, fs)
>> [y, fs] = audioread (filename, samples)
```
And about datatype:
```
>> [y,Fs] = audioread(filename,'native')
```
If the value is 'native' then the type of data depends on how the data is stored in the audio file.
### Step 4: Writing an audio file
Creating the ogg file:
For this purpose, we are going to generate an ogg file with values from a cosine. The sampling frequency that I will use is 44100 samples per second and the file will last for 10 seconds. The frequency of the cosine signal is 440 Hz.
```
>> filename='cosine.ogg';
>> fs=44100;
>> t=0:1/fs:10;
>> w=2*pi*440*t;
>> signal=cos(w);
>> audiowrite(filename, signal, fs);
```
This creates a file named 'cosine.ogg' in our workspace that contains the cosine signal.
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/cosinefile.png)
If we play the 'cosine.ogg' file then this will reproduce a 440Hz tone which is equivalent to an 'A' musical tone. If we want to see the values saved in the file we have to 'read' the file with the 'audioread' function. In a further tutorial, we will see how to write an audio file with two channels.
### Step 5: Playing an audio file
Octave, by default, has an audio player that we can use for testing purposes. Use the following functions as example:
```
>> [y,fs]=audioread('yourfile.ogg');
>> player=audioplayer(y, fs, 8)
scalar structure containing the fields:
BitsPerSample = 8
CurrentSample = 0
DeviceID = -1
NumberOfChannels = 1
Running = off
SampleRate = 44100
TotalSamples = 236473
Tag =
Type = audioplayer
UserData = [](0x0)
>> play(player);
```
In the next parts of the tutorial, we will see advanced audio processing features and possible use cases for scientific and commercial use.
--------------------------------------------------------------------------------
via: https://www.howtoforge.com/tutorial/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/
作者：[David Duarte][a]
译者：[译者ID](https://github.com/译者ID)
校对：[校对ID](https://github.com/校对ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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科学音频处理--怎样在 Ubuntu 上使用 Octave 对音频文件进行读写操作
================
Octave 是一个类似于 Linux 上的 Matlab 的软件，它有数量众多的函数和命令进行声音采集，记录，回放以及娱乐应用程序，研究，医学方面的音频信号的处理，这也包括任何其他的科学领域。在本教程中，我们会在 Ubuntu 上使用 Octave 的 4.0.0 版本读取音频文件，然后通过生成信号并且播放来模仿在各种情况下对音频信号的使用。
本教程中关注的不是安装和学习使用已有的音频处理软件，而是从设计和音频工程的角度理解它是如何工作的。
### 环境准备
首先是安装 octave，在 Ubuntu 终端运行下面的命令添加 Octave PPA 然后安装 Octave 。
```
sudo apt-add-repository ppa:octave/stable
sudo apt-get update
sudo apt-get install octave
```
### 步骤1：打开 Octave
在这一步中我们单击软件图标打开 Octave，可以通过单击下拉式按钮选择工作路径。
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/initial.png)
### 步骤2：音频信息
使用“audioinfo”命令查看要处理的音频文件的相关信息。
```
>> info = audioinfo ('testing.ogg')
```
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/audioinfo.png)
### 步骤3：读取音频文件
在本教程中我会使用 ogg 文件，因为读取这种文件的属性比较容易，比如采样，音频类型（stereo 和 mono）,信道数量等。必须声明的一点是教程中使用的所有的命令都是在 Octave 终端窗口中执行的。首先，我们必须要把这个 ogg 文件赋给一个变量。注意：文件必须在 Octave 的工作路径中。
```
>> file='yourfile.ogg'
```
```
>> [M, fs] = audioread(file)
```
这里的 M 是一个一列或两列的矩阵，取决于信道的数量，fs 是采样率。
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/reading.png)
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/matrix.png)
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/big/frequency.png)
下面的操作都可以读取音频文件：
```
>> [y, fs] = audioread (filename, samples)
>> [y, fs] = audioread (filename, datatype)
>> [y, fs] = audioread (filename, samples, datatype)
```
samples 指定开始帧和结束帧，datatype 指定返回的数据类型。可以为所有变量设置值：
```
>> samples = [1, fs)
>> [y, fs] = audioread (filename, samples)
```
数据类型：
```
>> [y,Fs] = audioread(filename,'native')
```
如果值是"native"，那么它的数据类型就依数据在音频文件中的存储情况而定。
### 步骤4：音频文件的写操作
新建一个 ogg 文件：
我们会创建一个带有余弦值的 ogg 文件。采样率是每秒 44100 次，这个文件最少进行 10 秒的采样。余弦信号的频率是 440 Hz。
```
>> filename='cosine.ogg';
>> fs=44100;
>> t=0:1/fs:10;
>> w=2*pi*440*t;
>> signal=cos(w);
>> audiowrite(filename, signal, fs);
```
这就在工作路径中创建了一个 'cosine.ogg' 文件，这个文件中包含余弦信号。
![](https://www.howtoforge.com/images/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/cosinefile.png)
播放这个 'cosine.ogg' 文件就会产生一个 440Hz 的 音调，这个音调正好是乐理中的 'A' 调。如果需要查看保存在文件中的值就必须使用 'audioread' 函数读取文件。在后续的教程中，我们会看到怎样在两个信道中读取一个音频文件。
### 步骤5：播放音频文件
Octave 有一个默认的音频播放器，可以用这个音频播放器进行测试。使用下面的函数：
```
>> [y,fs]=audioread('yourfile.ogg');
>> player=audioplayer(y, fs, 8)
scalar structure containing the fields:
BitsPerSample = 8
CurrentSample = 0
DeviceID = -1
NumberOfChannels = 1
Running = off
SampleRate = 44100
TotalSamples = 236473
Tag =
Type = audioplayer
UserData = [](0x0)
>> play(player);
```
在教程的后续，我们会进入音频处理的高级特性部分，可能会接触到一些科学和商业应用中的实例。
--------------------------------------------------------------------------------
via: https://www.howtoforge.com/tutorial/how-to-read-and-write-audio-files-with-octave-4-in-ubuntu/
作者：[David Duarte][a]
译者：[vim-kakali](https://github.com/vim-kakali)
校对：[校对ID](https://github.com/校对ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://twitter.com/intent/follow?original_referer=https%3A%2F%2Fwww.howtoforge.com%2Ftutorial%2Fhow-to-read-and-write-audio-files-with-octave-4-in-ubuntu%2F&ref_src=twsrc%5Etfw&region=follow_link&screen_name=howtoforgecom&tw_p=followbutton