mirror of
https://github.com/LCTT/TranslateProject.git
synced 2025-01-13 22:30:37 +08:00
Merge pull request #4495 from theArcticOcean/master
20160622 Part III - How to apply Advanced Mathematical Processing Effects on Audio files with Octave 4.0 on Ubuntu.md
This commit is contained in:
Xingyu.Wang
GitHub
commit
8ebf98cf06
@ -1,139 +0,0 @@
|
||||
translating by theArcticOcean.
|
||||
|
||||
Part III - How to apply Advanced Mathematical Processing Effects on Audio files with Octave 4.0 on Ubuntu
|
||||
=====
|
||||
|
||||
The third part of our Digital Audio processing tutorial series covers the signal Modulation, we explain how to apply Amplitude Modulation, Tremolo Effect, and Frequency Variation.
|
||||
|
||||
### Modulation
|
||||
|
||||
#### Amplitude Modulation
|
||||
|
||||
As its name implies, this effect varies the amplitude of a sinusoid according to the message to be transmitted. A sine wave is called a carrier because it carries the information. This type of modulation is used in some commercial broadcasting and transmission citizen bands (AM).
|
||||
|
||||
#### Why use the Amplitude Modulation?
|
||||
|
||||
**Modulation Radiation.**
|
||||
|
||||
If the communication channel is a free space, then antennas are required to radiate and receive the signal. It requires an efficient electromagnetic radiation antenna whose dimensions are of the same order of magnitude as the wavelength of the signal being radiated. Many signals, including audio components, have often 100 Hz or less. For these signals, it would be necessary to build antennas about 300 km in length if the signal were to be radiated directly. If signal modulation is used to print the message on a high-frequency carrier, let's say 100 MHz, then the antenna needs to have a length of over a meter (transverse length) only.
|
||||
|
||||
**Concentration modulation or multi-channeling.**
|
||||
|
||||
If more than one signal uses a single channel, modulation can be used for transferring different signals to different spectral positions allowing the receiver to select the desired signal. Applications that use concentration ("multiplexing") include telemetry data, stereo FM radio and long-distance telephony.
|
||||
|
||||
**Modulation to Overcome Limitations on equipment.**
|
||||
|
||||
The performance of signal processing devices such as filters and amplifiers, and the ease with which these devices can be constructed, depends on the situation of the signal in the frequency domain and the relationship between the higher frequency and low signal. Modulation can be used to transfer the signal to a position in the frequency domain where design requirements are met easier. The modulation can also be used to convert a "broadband signal" (a signal for which the ratio between the highest and lowest frequency is large) into a sign of "narrow band".
|
||||
|
||||
**Audio Effects**
|
||||
|
||||
Many audio effects use amplitude modulation due to the striking and ease with which it can handle such signals. We can name a few such as tremolo, chorus, flanger, etc. This utility is where we focus in this tutorial series.
|
||||
|
||||
### Tremolo effect
|
||||
|
||||
The tremolo effect is one of the simplest applications of amplitude modulation, to achieve this effect, we have to vary (multiply) the audio signal by a periodic signal, either sinusoidal or otherwise.
|
||||
|
||||
```
|
||||
>> tremolo='tremolo.ogg';
|
||||
>> fs=44100;
|
||||
>> t=0:1/fs:10;
|
||||
>> wo=2*pi*440*t;
|
||||
>> wa=2*pi*1.2*t;
|
||||
>> audiowrite(tremolo, cos(wa).*cos(wo),fs);
|
||||
```
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/tremolo.png)
|
||||
|
||||
This will generate a sinusoid-shaped signal which effect is like a 'tremolo'.
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/tremoloshape.png)
|
||||
|
||||
### Tremolo on real Audio Files
|
||||
|
||||
Now we will show the tremolo effect in the real world, First, we use a file previously recorded by a male voice saying 'A'. The plot for this signal is the following:
|
||||
|
||||
```
|
||||
>> [y,fs]=audioread('A.ogg');
|
||||
>> plot(y);
|
||||
```
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/avocalmale.png)
|
||||
|
||||
Now we have to create an enveloping sinusoidal signal with the following parameters:
|
||||
|
||||
```
|
||||
Amplitude = 1
|
||||
Frequency= 1.5Hz
|
||||
Phase = 0
|
||||
```
|
||||
|
||||
```
|
||||
>> t=0:1/fs:4.99999999;
|
||||
>> t=t(:);
|
||||
>> w=2*pi*1.5*t;
|
||||
>> q=cos(w);
|
||||
>> plot(q);
|
||||
```
|
||||
|
||||
Note: when we create an array of values of the time, by default, this is created in the form of columns, ie, 1x220500 values. To multiply this set of values must transpose it in rows (220500x1). This is the t=t(:) command
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/sinusoidal.png)
|
||||
|
||||
We will create a second ogg file which contains the resulting modulated signal:
|
||||
|
||||
```
|
||||
>> tremolo='tremolo.ogg';
|
||||
>> audiowrite(tremolo, q.*y,fs);
|
||||
```
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/tremsignal1.png)[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/tremolsignal1.png)
|
||||
|
||||
### Frequency Variation
|
||||
|
||||
We can vary the frequency to obtain quite interesting musical effects such as distortion, sound effects for movies and games among others.
|
||||
|
||||
#### Effect of sinusoidal frequency modulation
|
||||
|
||||
This is the code where the sinusoidal modulation frequency is shown, according to equation:
|
||||
|
||||
```
|
||||
Y=Ac*Cos(wo*Cos(wo/k))
|
||||
```
|
||||
|
||||
Where:
|
||||
|
||||
```
|
||||
Ac = Amplitude
|
||||
|
||||
wo = fundamental frequency
|
||||
|
||||
k = scalar divisor
|
||||
```
|
||||
|
||||
```
|
||||
>> fm='fm.ogg';
|
||||
>> fs=44100;
|
||||
>> t=0:1/fs:10;
|
||||
>> w=2*pi*442*t;
|
||||
>> audiowrite(fm, cos(cos(w/1500).*w), fs);
|
||||
>> [y,fs]=audioread('fm.ogg');
|
||||
>> figure (); plot (y);
|
||||
```
|
||||
|
||||
The plot of the signal is:
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/fmod.png)
|
||||
|
||||
You can use almost any type of periodic function as the frequency modulator. For this example, we only used a sine function here. Please feel free to experiment with changing the frequencies of the functions, mixing with other functions or change, even, the type of function.
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://www.howtoforge.com/tutorial/ubuntu-octave-audio-processing-part-3/
|
||||
|
||||
作者：[David Duarte][a]
|
||||
译者：[译者ID](https://github.com/译者ID)
|
||||
校对：[校对者ID](https://github.com/校对者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://www.howtoforge.com/tutorial/ubuntu-octave-audio-processing-part-3/
|
||||
@ -0,0 +1,136 @@
|
||||
第3部分 - 如何使用Ubuntu系统上Octave 4.0的先进数学技术处理音频文件
|
||||
=====
|
||||
|
||||
我们的数字音频处理技术第三部分涵盖了信号调制内容，将解释如何进行调幅,颤音效果,和频率变化。
|
||||
### 调制
|
||||
|
||||
#### 调幅
|
||||
|
||||
正如它的名字暗示的那样， 影响正弦信号的振幅变化依据传递的信息不断改变。正弦波因为承载者大量的信息被称作载波。这种调制技术被用于许多的商业广播和市民信息传输波段(AM).
|
||||
|
||||
#### 为何要使用调幅技术？
|
||||
|
||||
**调制发射.**
|
||||
|
||||
假设信道是免费资源，我们需要天线发射和接收信号。这要求有效的电磁信号发射天线，它的大小和要被发射的信号的波长应该是同一数量级。很多信号，包括音频成分，通常100赫兹或更少。对于这些信号，如果直接发射，我们就需要建立300公里的天线。如果信号调制用于在100MZ的高频载波中打印信息，那么天线仅仅需要1米（横向长度）。
|
||||
|
||||
**集中调制与多通道.**
|
||||
|
||||
假设多个信号占用一个通道，可以调制不同的信号到接收特定信号的不同位置。使用集中调制（“复用”）的应用有遥感探测数据，立体声调频收音机和长途电话。
|
||||
|
||||
**克服设备限制的调制.**
|
||||
|
||||
信号处理设备，比如过滤器，放大器，以及可以被重新创建的设备它们的性能依赖于信号在频域中的境况以及高频率和低频信号的关系。调制可以用于传递信号在频域中的位置，更容易满足设计的要求。调制也可以将“宽带信号“（高频和低频的比例很大的信号）转换成”窄带“信号
|
||||
|
||||
**音频特效**
|
||||
|
||||
许多音频特效由于引人注目和处理信号的便捷性使用了调幅技术。我们可以说出很多，比如颤音、合唱、镶边等等。这种实用性就是我们关注它的原因。
|
||||
|
||||
### 颤音效果
|
||||
|
||||
颤音效果是调幅最简单的应用，为实现这样的效果，我们会用周期信号改变（乘）音频信号，使用正弦或其他。
|
||||
|
||||
```
|
||||
>> tremolo='tremolo.ogg';
|
||||
>> fs=44100;
|
||||
>> t=0:1/fs:10;
|
||||
>> wo=2*pi*440*t;
|
||||
>> wa=2*pi*1.2*t;
|
||||
>> audiowrite(tremolo, cos(wa).*cos(wo),fs);
|
||||
```
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/tremolo.png)
|
||||
|
||||
这将创造一个正弦形状的信号，它的效果就像‘颤音’。
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/tremoloshape.png)
|
||||
|
||||
### 在真实音频文件中的颤音
|
||||
|
||||
现在我们将展示真实世界中的颤音效果。首先，我们使用之前记录过男性发声‘A’的音频文件。这个信号图就像下面这样：
|
||||
|
||||
```
|
||||
>> [y,fs]=audioread('A.ogg');
|
||||
>> plot(y);
|
||||
```
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/avocalmale.png)
|
||||
|
||||
现在我们将创建一个完整的正弦信号，使用如下的参数：
|
||||
|
||||
```
|
||||
Amplitude = 1
|
||||
Frequency= 1.5Hz
|
||||
Phase = 0
|
||||
```
|
||||
|
||||
```
|
||||
>> t=0:1/fs:4.99999999;
|
||||
>> t=t(:);
|
||||
>> w=2*pi*1.5*t;
|
||||
>> q=cos(w);
|
||||
>> plot(q);
|
||||
```
|
||||
|
||||
注意： 当我们创建一组时间值时，默认情况下，它是以列的格式呈现，如, 1x220500的值。为了乘以这样的值，必须将其变成行的形式(220500x1). 这就是t=t(:)命令的作用。
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/sinusoidal.png)
|
||||
|
||||
我们将创建第二份ogg音频格式的文件，它包含了如下的调制信号：
|
||||
|
||||
```
|
||||
>> tremolo='tremolo.ogg';
|
||||
>> audiowrite(tremolo, q.*y,fs);
|
||||
```
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/tremsignal1.png)[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/tremolsignal1.png)
|
||||
|
||||
### 频率变化
|
||||
|
||||
我们可以改变频率保持一些有趣的音效，比如原音变形，电影音效，多人比赛。
|
||||
|
||||
#### 正弦频率调制的影响
|
||||
|
||||
这是正弦调制频率变化的演示代码，根据方程：
|
||||
|
||||
```
|
||||
Y=Ac*Cos(wo*Cos(wo/k))
|
||||
```
|
||||
|
||||
Where:
|
||||
|
||||
```
|
||||
Ac = Amplitude
|
||||
|
||||
wo = fundamental frequency
|
||||
|
||||
k = scalar divisor
|
||||
```
|
||||
|
||||
```
|
||||
>> fm='fm.ogg';
|
||||
>> fs=44100;
|
||||
>> t=0:1/fs:10;
|
||||
>> w=2*pi*442*t;
|
||||
>> audiowrite(fm, cos(cos(w/1500).*w), fs);
|
||||
>> [y,fs]=audioread('fm.ogg');
|
||||
>> figure (); plot (y);
|
||||
```
|
||||
|
||||
信号图：
|
||||
|
||||
[](https://www.howtoforge.com/images/ubuntu-octave-audio-processing-part-3/big/fmod.png)
|
||||
|
||||
你可以使用几乎任何类型的周期函数频率调制。本例中，我们仅仅用了一个正弦函数。请大胆的改变函数频率，用复合函数，甚至改变函数的类型。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
经由: https://www.howtoforge.com/tutorial/ubuntu-octave-audio-processing-part-3/
|
||||
|
||||
作者：[David Duarte][a]
|
||||
译者：[theArcticOcean](https://github.com/theArcticOcean)
|
||||
校对：[校对者ID](https://github.com/校对者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://www.howtoforge.com/tutorial/ubuntu-octave-audio-processing-part-3/
|
||||
Loading…
Reference in New Issue
Block a user