java - 如何计算java中音频信号的电平/幅度/分贝？

Question

我想在 java 中为麦克风创建一个音频电平表来检查输入的音量。它应该看起来像操作系统之一。我不是在问 gui。它只是计算

产生的字节流中的音频电平

n = targetDataLine.read( tempBuffer , 0 , tempBuffer.length );

所以我已经有一些正在运行的东西，但它甚至离我的操作系统 (windows) 的电平表还差得很远，它卡在中间。我的值介于 0 和 100 之间，这很好，但在中间音量中，无论输入有多大声，它都会停留在 60 左右。

我现在是这样计算的:

            amplitude = 0;
        for (int j = 0; j < tempBuffer.length; j = j +2 ){
            if (tempBuffer[j] > tempBuffer[j+1])
                amplitude = amplitude + tempBuffer[j] - tempBuffer[j+1];
            else amplitude = amplitude + tempBuffer[j + 1] - tempBuffer[j];
        }
        amplitude = amplitude / tempBuffer.length * 2;

是否有更好/更精确的方法来计算音频电平以进行监控？还是我可能犯了一个重大错误？

这是我的音频格式:

public static AudioFormat getAudioFormat(){
    float sampleRate = 20000.0F;
    //8000,11025,16000,22050,44100
    int sampleSizeInBits = 16;
    //8,16
    int channels = 1;
    //1,2
    boolean signed = true;
    //true,false
    boolean bigEndian = false;
    //true,false
    return new AudioFormat( sampleRate, sampleSizeInBits, channels, signed, bigEndian );
    //return new AudioFormat(AudioFormat.Encoding.PCM_SIGNED, 8000.0F, 8, 1, 1, 8000.0F, false);
}

Answer 1

主要问题似乎是您读取的音频数据不正确。

具体来说，我不太确定这段摘录是什么意思:

if (tempBuffer[j] > tempBuffer[j+1])
    ... tempBuffer[j] - tempBuffer[j+1];
else
    ... tempBuffer[j + 1] - tempBuffer[j];

但是无论如何，由于您正在记录 16 位数据，因此字节数组中的字节本身没有意义。每个字节仅代表每个样本中 1/2 的位。在对它们进行任何操作之前，您需要将它们“解包”为 int、float 等。对于原始 LPCM，连接字节是通过移动它们并将它们组合在一起来完成的。

这是一个 MCVE，用于演示 Java 中的基本电平表(RMS 和简单峰值保持)。

import javax.swing.SwingUtilities;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JComponent;

import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Color;
import java.awt.Dimension;
import javax.swing.border.EmptyBorder;

import javax.sound.sampled.AudioFormat;
import javax.sound.sampled.TargetDataLine;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.LineUnavailableException;

public class LevelMeter extends JComponent {
    private int meterWidth = 10;

    private float amp = 0f;
    private float peak = 0f;

    public void setAmplitude(float amp) {
        this.amp = Math.abs(amp);
        repaint();
    }

    public void setPeak(float peak) {
        this.peak = Math.abs(peak);
        repaint();
    }

    public void setMeterWidth(int meterWidth) {
        this.meterWidth = meterWidth;
    }

    @Override
    protected void paintComponent(Graphics g) {
        int w = Math.min(meterWidth, getWidth());
        int h = getHeight();
        int x = getWidth() / 2 - w / 2;
        int y = 0;

        g.setColor(Color.LIGHT_GRAY);
        g.fillRect(x, y, w, h);

        g.setColor(Color.BLACK);
        g.drawRect(x, y, w - 1, h - 1);

        int a = Math.round(amp * (h - 2));
        g.setColor(Color.GREEN);
        g.fillRect(x + 1, y + h - 1 - a, w - 2, a);

        int p = Math.round(peak * (h - 2));
        g.setColor(Color.RED);
        g.drawLine(x + 1, y + h - 1 - p, x + w - 1, y + h - 1 - p);
    }

    @Override
    public Dimension getMinimumSize() {
        Dimension min = super.getMinimumSize();
        if(min.width < meterWidth)
            min.width = meterWidth;
        if(min.height < meterWidth)
            min.height = meterWidth;
        return min;
    }

    @Override
    public Dimension getPreferredSize() {
        Dimension pref = super.getPreferredSize();
        pref.width = meterWidth;
        return pref;
    }

    @Override
    public void setPreferredSize(Dimension pref) {
        super.setPreferredSize(pref);
        setMeterWidth(pref.width);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame("Meter");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

                JPanel content = new JPanel(new BorderLayout());
                content.setBorder(new EmptyBorder(25, 50, 25, 50));

                LevelMeter meter = new LevelMeter();
                meter.setPreferredSize(new Dimension(9, 100));
                content.add(meter, BorderLayout.CENTER);

                frame.setContentPane(content);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                new Thread(new Recorder(meter)).start();
            }
        });
    }

    static class Recorder implements Runnable {
        final LevelMeter meter;

        Recorder(final LevelMeter meter) {
            this.meter = meter;
        }

        @Override
        public void run() {
            AudioFormat fmt = new AudioFormat(44100f, 16, 1, true, false);
            final int bufferByteSize = 2048;

            TargetDataLine line;
            try {
                line = AudioSystem.getTargetDataLine(fmt);
                line.open(fmt, bufferByteSize);
            } catch(LineUnavailableException e) {
                System.err.println(e);
                return;
            }

            byte[] buf = new byte[bufferByteSize];
            float[] samples = new float[bufferByteSize / 2];

            float lastPeak = 0f;

            line.start();
            for(int b; (b = line.read(buf, 0, buf.length)) > -1;) {

                // convert bytes to samples here
                for(int i = 0, s = 0; i < b;) {
                    int sample = 0;

                    sample |= buf[i++] & 0xFF; // (reverse these two lines
                    sample |= buf[i++] << 8;   //  if the format is big endian)

                    // normalize to range of +/-1.0f
                    samples[s++] = sample / 32768f;
                }

                float rms = 0f;
                float peak = 0f;
                for(float sample : samples) {

                    float abs = Math.abs(sample);
                    if(abs > peak) {
                        peak = abs;
                    }

                    rms += sample * sample;
                }

                rms = (float)Math.sqrt(rms / samples.length);

                if(lastPeak > peak) {
                    peak = lastPeak * 0.875f;
                }

                lastPeak = peak;

                setMeterOnEDT(rms, peak);
            }
        }

        void setMeterOnEDT(final float rms, final float peak) {
            SwingUtilities.invokeLater(new Runnable() {
                @Override
                public void run() {
                    meter.setAmplitude(rms);
                    meter.setPeak(peak);
                }
            });
        }
    }
}

注意格式转换是硬编码的。

您还可以看到 "How do I use audio sample data from Java Sound?"我详细解释了如何从原始字节中解压音频数据。

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