Android -录制音频时的音频剪辑(波峰/峰值剪辑和介于两者之间的周期性0比特值)

在 Android 上录制音频时，音频剪辑（Clipping）是一个常见的问题。音频剪辑通常发生在音频信号的振幅超过了录音设备的最大可处理范围，导致信号被截断。这会导致音频失真，产生不愉快的声音。

1. 检测音频剪辑

要检测音频剪辑，可以分析录制的音频数据，寻找波峰（Peak Clipping）和周期性 0 比特值（Periodic Zero Bit Values）。以下是一些步骤和代码示例，展示如何在 Android 上检测和处理音频剪辑。

1.1 设置音频录制

首先，设置音频录制器：

import android.media.AudioFormat;
import android.media.AudioRecord;
import android.media.MediaRecorder;

public class AudioClipDetector {
    private static final int SAMPLE_RATE = 44100;
    private static final int BUFFER_SIZE = AudioRecord.getMinBufferSize(SAMPLE_RATE,
            AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT);

    private AudioRecord audioRecord;
    private boolean isRecording = false;

    public void startRecording() {
        audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, SAMPLE_RATE,
                AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT, BUFFER_SIZE);

        audioRecord.startRecording();
        isRecording = true;

        new Thread(new AudioClipDetectionRunnable()).start();
    }

    public void stopRecording() {
        if (audioRecord != null) {
            isRecording = false;
            audioRecord.stop();
            audioRecord.release();
            audioRecord = null;
        }
    }

    private class AudioClipDetectionRunnable implements Runnable {
        @Override
        public void run() {
            short[] buffer = new short[BUFFER_SIZE];
            while (isRecording) {
                int read = audioRecord.read(buffer, 0, BUFFER_SIZE);
                if (read > 0) {
                    detectClipping(buffer, read);
                }
            }
        }
    }

    private void detectClipping(short[] buffer, int read) {
        // 检测音频剪辑的逻辑
    }
}

1.2 检测波峰剪辑

波峰剪辑发生在音频信号的振幅超过了录音设备的最大可处理范围。对于 16 位 PCM 音频，最大振幅为 32767，最小振幅为 -32768。

private void detectClipping(short[] buffer, int read) {
    for (int i = 0; i < read; i++) {
        if (buffer[i] >= 32767 || buffer[i] <= -32768) {
            // 检测到波峰剪辑
            System.out.println("Clipping detected at sample " + i);
        }
    }
}

1.3 检测周期性 0 比特值

周期性 0 比特值通常表示音频信号中存在静音或信号丢失。可以通过检测连续的 0 值来识别这种情况。

private void detectClipping(short[] buffer, int read) {
    int zeroCount = 0;
    for (int i = 0; i < read; i++) {
        if (buffer[i] == 0) {
            zeroCount++;
        } else {
            zeroCount = 0;
        }

        if (zeroCount > SOME_THRESHOLD) {
            // 检测到周期性 0 比特值
            System.out.println("Periodic zero bit values detected at sample " + i);
        }
    }
}

2. 处理音频剪辑

检测到音频剪辑后，可以采取一些措施来处理它，例如：

降低录音增益：如果录音设备支持，可以降低录音增益以减少剪辑。
应用动态范围压缩：在录音过程中应用动态范围压缩（Dynamic Range Compression, DRC）以减少信号的动态范围。
通知用户：通知用户音频剪辑问题，并建议他们调整录音环境或设备设置。

3. 完整示例

以下是一个完整的示例，展示如何在 Android 上检测和处理音频剪辑：

import android.media.AudioFormat;
import android.media.AudioRecord;
import android.media.MediaRecorder;

public class AudioClipDetector {
    private static final int SAMPLE_RATE = 44100;
    private static final int BUFFER_SIZE = AudioRecord.getMinBufferSize(SAMPLE_RATE,
            AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT);
    private static final int CLIPPING_THRESHOLD = 32767;
    private static final int ZERO_THRESHOLD = 100; // 根据需要调整

    private AudioRecord audioRecord;
    private boolean isRecording = false;

    public void startRecording() {
        audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, SAMPLE_RATE,
                AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT, BUFFER_SIZE);

        audioRecord.startRecording();
        isRecording = true;

        new Thread(new AudioClipDetectionRunnable()).start();
    }

    public void stopRecording() {
        if (audioRecord != null) {
            isRecording = false;
            audioRecord.stop();
            audioRecord.release();
            audioRecord = null;
        }
    }

    private class AudioClipDetectionRunnable implements Runnable {
        @Override
        public void run() {
            short[] buffer = new short[BUFFER_SIZE];
            while (isRecording) {
                int read = audioRecord.read(buffer, 0, BUFFER_SIZE);
                if (read > 0) {
                    detectClipping(buffer, read);
                }
            }
        }
    }

    private void detectClipping(short[] buffer, int read) {
        int zeroCount = 0;
        for (int i = 0; i < read; i++) {
            if (buffer[i] >= CLIPPING_THRESHOLD || buffer[i] <= -CLIPPING_THRESHOLD) {
                // 检测到波峰剪辑
                System.out.println("Clipping detected at sample " + i);
            }

            if (buffer[i] == 0) {
                zeroCount++;
            } else {
                zeroCount = 0;
            }

            if (zeroCount > ZERO_THRESHOLD) {
                // 检测到周期性 0 比特值
                System.out.println("Periodic zero bit values detected at sample " + i);
            }
        }
    }
}

通过这种方式，你可以在 Android 上检测和处理音频剪辑问题，确保录制的音频质量。