matlab之「audioread」函數幫助文檔翻譯

課 程 設 計 （1） 

原文

audioread

Read audio file

Syntax

• [y,Fs] = audioread(filename)

• [y,Fs] = audioread(filename,samples)

• [y,Fs] = audioread(___,dataType)

Description

[y,Fs] = audioread(filename) reads data from the file named filename, and returns sampled data, y, and a sample rate for that data, Fs.

[y,Fs] = audioread(filename,samples) reads the selected range of audio samples in the file, where samples is a vector of the form [start,finish].

[y,Fs] = audioread(___,dataType) returns sampled data in the data range corresponding to the dataType of 'native' or 'double', and can include any of the input arguments in previous syntaxes.

Examples

Read Complete Audio File

Create a WAVE file from the example file handel.mat, and read the file back into MATLAB^®.

Create a WAVE (.wav) file in the current folder.

load handel.mat

filename = 'handel.wav';
audiowrite(filename,y,Fs);
clear y Fs

Read the data back into MATLAB using audioread.

[y,Fs] = audioread('handel.wav');

Play the audio.

sound(y,Fs);

Read Portion of Audio File

Create a FLAC file from the example file handel.mat, and then read only the first 2 seconds.

Create a FLAC (.flac) file in the current folder.

load handel.mat

filename = 'handel.flac';
audiowrite(filename,y,Fs);

Read only the first 2 seconds.

samples = [1,2*Fs];
clear y Fs
[y,Fs] = audioread(filename,samples);

Play the samples.

sound(y,Fs);

Return Audio in Native Integer Format

Create a FLAC file and read the first 2 seconds according to the previous Example. Then, view the data type of the sampled data y.

whos y

  Name          Size             Bytes  Class     Attributes

  y         16384x1             131072  double   

The data type of y is double.

Request audio data in the native format of the file, and then view the data type of the sampled data y.

[y,Fs] = audioread(filename,'native');
whos y

  Name          Size            Bytes  Class    Attributes

  y         16384x1             32768  int16              

The data type of y is now int16.

Input Arguments

filename — Name of file to readstring

Name of file to read, specified as a string that includes the file extension. If a path is specified, it can be absolute, relative or partial.

Example: 'myFile.mp3'

Example: '../myFile.mp3'

Example: 'C:\temp\myFile.mp3'

audioread supports the following file formats.

Platform Support	File Format
All platforms	WAVE (.wav)
	OGG (.ogg)
	FLAC (.flac)
	AU (.au)
	AIFF (.aiff, .aif)
	AIFC (.aifc)
Windows® 7 (or later), Macintosh, and Linux®	MP3 (.mp3)
	MPEG-4 AAC (.m4a, .mp4)

On Windows platforms prior to Windows 7, audioread does not read WAVE files with MP3 encoded data.

On Windows 7 (or later) platforms, audioread might also read any files supported by Windows Media^® Foundation.

On Linux platforms, audioread might also read any files supported by GStreamer.

audioread can extract audio from MPEG-4 (.mp4, .m4v) video files on Windows 7 or later, Macintosh, and Linux, and from Windows Media Video (.wmv) and AVI (.avi) files on Windows 7 (or later) and Linux platforms.

samples — Audio samples to read[1,inf] (default) | two-element vector of positive scalar integers

Audio samples to read, specified as a two-element vector of the form [start,finish], where start and finish are the first and last samples to read, and are positive scalar integers.

• start must be less than or equal to finish.

• start and finish must be less than the number of audio samples in the file,

• You can use inf to indicate the last sample in the file.

Note:   When reading a portion of some MP3 files on Windows 7 platforms, audioread might read a shifted range of samples. This is due to a limitation in the underlying Windows Media Foundation framework. When reading a portion of MP3 and M4A files on Linux platforms, audioread might read a shifted range of samples. This is due to a limitation in the underlying GStreamer framework.

Example: [1,100]

Data Types: double

dataType — Data format of audio data, y'double' (default) | 'native'

Data format of audio data,y, specified as one of the following strings:

'double'	Double-precision normalized samples.
'native'	Samples in the native format found in the file.

For compressed audio formats, such as MP3 and MPEG-4 AAC that do not store data in integer form, 'native' defaults to 'single'.

Output Arguments

y — Audio datamatrix

Audio data in the file, returned as an m-by-n matrix, where m is the number of audio samples read and n is the number of audio channels in the file.

• If you do not specify dataType, or dataType is 'double', then y is of type double, and matrix elements are normalized values between −1.0 and 1.0.

• If dataType is 'native', then y can be one of several MATLAB data types, depending on the file format and the BitsPerSample value of the input file. Call audioinfo to determine theBitsPerSample value of the file.

  File Format	BitsPerSample	Data Type of y	Data Range of y
  WAVE (.wav)	8	uint8	0 ≤ y ≤ 255
  	16	int16	-32768 ≤ y ≤ +32767
  	24	int32	-2^32 ≤ y ≤ 2^32–1
  	32	int32	-2^32 ≤ y ≤ 2^32–1
  	32	single	-1.0 ≤ y ≤ +1.0
  	64	double	-1.0 ≤ y ≤ +1.0
  FLAC (.flac)	8	uint8	0 ≤ y ≤ 255
  	16	int16	-32768 ≤ y ≤ +32767
  	24	int32	-2^32 ≤ y ≤ 2^32–1
  MP3 (.mp3), MPEG-4 AAC (.m4a, .mp4), OGG (.ogg), and certain compressed WAVE files	N/A	single	-1.0 ≤ y ≤ +1.0

Note:   Where y is single or double and the BitsPerSample is 32 or 64, values in y might exceed −1.0 or +1.0.

Fs — Sample ratepositive scalar

Sample rate, in hertz, of audio data y, returned as a positive scalar.

Limitations

• For MP3, MPEG-4 AAC, and AVI audio files on Windows 7 or later and Linux platforms, audioread might read fewer samples than expected. On Windows 7 platforms, this is due to a limitation in the underlying Media Foundation framework. On Linux platforms, this is due to a limitation in the underlying GStreamer framework. If you require sample-accurate reading, work with WAV or FLAC files.

• On Linux platforms, audioread reads MPEG-4 AAC files that contain single-channel data as stereo data.

翻譯

調用結構&描述

　　[y, Fs] =audioread(filename)

　　從以「filename」爲文件名的文件中讀取數據，並返回抽樣數據y和此數據的抽樣率Fs 。

　　[y, Fs] =audioread(filename， samples)

　　以選定範圍從文件中讀取音頻樣本，其中 samples 是具備[start， finish]形式的向量。

　　[y, Fs] =audioread( ____， dataType)

　　返回數據域中與 dataType 相對應的採樣數據，dataType 可選「native（本地類型）」或「double（雙精度型）」。

例子

　　能夠本身從本地音樂裏面選擇音樂來測試。可是建議適當縮減音頻長度，否則計算量會比較大，有可能卡死電腦。剪輯音頻可使用「格式工廠」，它也能用來轉換文件格式。

輸入　　一、對於輸入文件，表中給的信息已經很詳細了，".wav"格式的音頻是必定支持的，通用的".mp3"格式在win7以上及Linux系統上都是能夠讀取的。

　　二、 對於輸入參數 samples ，在第一種調用結構中實際上是隱藏了 [1, inf] 的默認samples參數，意思是從文件頭讀到文件尾。在第二種調用格式裏面咱們能夠指定讀取的參數範圍。要注意 start, finish 兩個參數都是正整數，並且他們的大小不能超出抽樣個數。這個很容易理解，超出了源文件的抽樣範圍就不可能有數據。在使用中，能夠用 [start, inf] 表示從 start 讀到文件尾。

　　注意：當在win7平臺上讀取MP3以及在Linux上讀取MP3&M4A格式文件時，可能會出現讀取範圍轉移的現象，這是因爲底層Windows Media Foundation框架的侷限性形成的。

　　三、dataType有兩種取值，native 或 double 。默認狀況下，native 爲單精度類型 single 。

輸出

　　y 爲音頻數據，是一個mxn 的矩陣，m是讀取文件的抽樣個數，n是讀取文件的音頻信道個數。

　　　　· 在未明確 dataType 和 dataType 取 double 時，y 的類型也是 double。y 的元素爲值介於-1.0和1.0之間的規範化值。

　　　　· 若是 dataType 取 native，y 能夠爲matlab所容許的幾種數據類型之一。至於爲哪種類型取決於輸入文件的類型，這種對應關係在上面給出的表中。

　　注意：當 y 爲單精度或雙精度數， 且 BitPerSample 爲32或64時，y 的值有可能超出 -1.0~1.0。

侷限

　　· 對於 MP3, MPEG-4 AAC, AVI音頻文件，在win7及更高版本和Linux平臺上，有可能會出現抽樣個數比預期要少的現象。

　　· 在Linux上讀取MPEG-4 AAC文件時，即便是單聲道數據文件，也會當成立體聲文件來讀。