如何生成具有正弦波和用户定义的持续时间和频率的.wav文件

Question

下面的代码应该创建一个包含正弦波的文件。在典型的频率(220Hz, 440Hz, 880Hz)下，它表现得很好，但在许多其他频率下，它就不那么好了，比如225Hz, 883Hz等等。我该怎么做才能得到任意频率的正弦波?

import java.lang.Math;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
public class CreateSine 
{
    static String fileNameString = "Sine.wav";
    static File file = new File(fileNameString);
    static String filePath = file.getAbsolutePath();
    static RandomAccessFile raw;
    static int byteCount = 0;
    static double pow215 = Math.pow(2, 15);
    static float freq = 440.0f;
    static int sRate = 44100;
    static int bitDepth = 16;
    static int nChannels = 1;
    static int dur = 1;
    static float changeRate = (float)((2.0 * Math.PI * freq) / sRate);
    public static void main(String[] args)
    {
        try
        {
            raw = new RandomAccessFile(filePath, "rw");
            raw.setLength(0); // Set file length to 0, to prevent unexpected behavior in case the file already existed
            raw.writeBytes("RIFF");
            raw.writeInt(0); // Final file size not known yet, write 0. This is = sample count + 36 bytes from header.
            raw.writeBytes("WAVE");
            raw.writeBytes("fmt ");
            raw.writeInt(Integer.reverseBytes(16)); // Sub-chunk size, 16 for PCM
            raw.writeShort(Short.reverseBytes((short) 1)); // AudioFormat, 1 for PCM
            raw.writeShort(Short.reverseBytes((short)nChannels));// Number of channels, 1 for mono, 2 for stereo
            raw.writeInt(Integer.reverseBytes(sRate)); // Sample rate
            raw.writeInt(Integer.reverseBytes(sRate*bitDepth*nChannels/8)); // Byte rate, SampleRate*NumberOfChannels*bitDepth/8
            raw.writeShort(Short.reverseBytes((short)(nChannels*bitDepth/8))); // Block align, NumberOfChannels*bitDepth/8
            raw.writeShort(Short.reverseBytes((short)bitDepth)); // Bit Depth
            raw.writeBytes("data");
            raw.writeInt(0); // Data chunk size not known yet, write 0. This is = sample count.
        }
        catch(IOException e)
        {
            System.out.println("I/O exception occured while writing data");
        }
        for (int i = 0; i < sRate*dur; i++)
        {
            writeSample( (float)Math.sin( i * changeRate ) );
        }
        closeFile();
        System.out.print("Finished");
    }
    static void writeSample(float floatValue)
    {
        try 
        {
            short hexSample = (short)((floatValue * pow215));
            raw.writeShort(Short.reverseBytes(hexSample));
            byteCount += 2;
        }
        catch(IOException e)
        {
            System.out.println("I/O exception occured while writing data");
        }
    }
    static void closeFile() 
    {
        try 
        {
            raw.seek(4); // Write size to RIFF header
            raw.writeInt(Integer.reverseBytes(byteCount + 36));
            raw.seek(40); // Write size to Subchunk2Size field
            raw.writeInt(Integer.reverseBytes(byteCount));
            raw.close();
        }
        catch(IOException e)
        {
            System.out.println("I/O exception occured while closing output file");
        }
    }
}

谢谢你的帮助。

Answer 1

你的问题并没有真正描述问题是什么，只是说它不好。我要大胆猜测，你在从float到int的转换中得到了剪辑。

• sin函数能输出的最大值为1.0。
• 将输出乘以2^15，即32768。
• 最大正号短码是32767。

您在不同频率下经历剪切的原因是正弦函数在sin(1+4k*pi/2)处仅达到1.0，其中k是任意正整数。某些频率(例如441Hz)会经常达到1.0，而其他频率则不会。

解决方法是将浮点数乘以((2^15)-1)

Answer 2

更正后的代码如下，而不是乘以每个float: float * 2^15，我正在做:float * 0x7FFF，正如夹克所指出的，变成:float * ((2^15)-1):

import java.lang.Math;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
public class CreateSine 
{
    static String fileNameString;
    static File file;
    static String filePath;
    static RandomAccessFile raw;
    static int byteCount = 0;
    static float freq;
    static int sRate = 44100;
    static int bitDepth = 16;
    static int nChannels = 1;
    static int dur;
    static float changeRate;
    public static void main(String[] args)
    {
        freq = Float.parseFloat(args[0]);
        changeRate = (float)((2.0 * Math.PI * freq) / sRate);
        dur = Integer.parseInt(args[1]);
        fileNameString = (String)args[2] + ".wav";
        file = new File(fileNameString);
        filePath = file.getAbsolutePath();
        try
        {
            raw = new RandomAccessFile(filePath, "rw");
            raw.setLength(0); // Set file length to 0, to prevent unexpected behavior in case the file already existed
            raw.writeBytes("RIFF");
            raw.writeInt(0); // Final file size not known yet, write 0. This is = sample count + 36 bytes from header.
            raw.writeBytes("WAVE");
            raw.writeBytes("fmt ");
            raw.writeInt(Integer.reverseBytes(16)); // Sub-chunk size, 16 for PCM
            raw.writeShort(Short.reverseBytes((short) 1)); // AudioFormat, 1 for PCM
            raw.writeShort(Short.reverseBytes((short)nChannels));// Number of channels, 1 for mono, 2 for stereo
            raw.writeInt(Integer.reverseBytes(sRate)); // Sample rate
            raw.writeInt(Integer.reverseBytes(sRate*bitDepth*nChannels/8)); // Byte rate, SampleRate*NumberOfChannels*bitDepth/8
            raw.writeShort(Short.reverseBytes((short)(nChannels*bitDepth/8))); // Block align, NumberOfChannels*bitDepth/8
            raw.writeShort(Short.reverseBytes((short)bitDepth)); // Bit Depth
            raw.writeBytes("data");
            raw.writeInt(0); // Data chunk size not known yet, write 0. This is = sample count.
        }
        catch(IOException e)
        {
            System.out.println("I/O exception occured while writing data");
        }
        for (int i = 0; i < sRate*dur; i++)
        {
            writeSample( (float)Math.sin( i * changeRate ) );
        }
        closeFile();
        System.out.print("Finished");
    }
    static void writeSample(float floatValue)
    {
        try 
        {
            char shortSample = (char)( (floatValue)*0x7FFF );
            raw.writeShort(Character.reverseBytes(shortSample));
            byteCount += 2;
        }
        catch(IOException e)
        {
            System.out.println("I/O exception occured while writing data");
        }
    }
    static void closeFile() 
    {
        try 
        {
            raw.seek(4); // Write size to RIFF header
            raw.writeInt(Integer.reverseBytes(byteCount + 36));
            raw.seek(40); // Write size to Subchunk2Size field
            raw.writeInt(Integer.reverseBytes(byteCount));
            raw.close();
        }
        catch(IOException e)
        {
            System.out.println("I/O exception occured while closing output file");
        }
    }
}