J2ME/Blackberry - 获取音频信号幅度级别？

Question

j2me中可以测量JSR-135播放器录制的音频信号幅度吗？
我知道我可以访问缓冲区，但那又怎样呢？

目标型号 Bold 9000，支持格式 PCM 和 AMR。我应该使用哪种格式？

参见 Blackberry 录音示例代码
如何 - 在 BlackBerry 智能手机上录制音频

谢谢！

Answer 1

获取原始 PCM 信号电平

• 使用菜单和拨轮在图表中放大/缩小以及左/右移动。
• 音频格式：原始 8000 Hz 16 位单声道 PCM。
• 在 Bold 9000 RIM OS 4.6 上进行测试
• 算法应该适用于任何支持 j2me 和 pcm 的移动设备，当然实现可能需要更改。

使用线程进行录音：

class VoiceNotesRecorderThread extends Thread {

    private Player _player;
    private RecordControl _rcontrol;
    private ByteArrayOutputStream _output;
    private byte _data[];

    VoiceNotesRecorderThread() {
    }

    public void run() {
        try {
            _player = Manager
                .createPlayer("capture://audio?encoding=audio/basic");
            _player.realize();
            _rcontrol = (RecordControl) _player
                .getControl("RecordControl");
            _output = new ByteArrayOutputStream();
            _rcontrol.setRecordStream(_output);
            _rcontrol.startRecord();
            _player.start();
        } catch (final Exception e) {
            UiApplication.getUiApplication().invokeAndWait(new Runnable() {
                public void run() {
                    Dialog.inform(e.toString());
                }
            });
        }
    }

    public void stop() {
        try {
            _rcontrol.commit();
            _data = _output.toByteArray();
            _output.close();
            _player.close();
        } catch (Exception e) {
            synchronized (UiApplication.getEventLock()) {
                Dialog.inform(e.toString());
            }
        }
    }

    byte[] getData() {
        return _data;
    }
}

以及使用 byte[] 缓冲区绘制图形的方法：

private Bitmap getGraph(byte[] buffer, int zoom, int startFrom) {
    Bitmap result = new Bitmap(Display.getWidth(), Display.getHeight());
    Graphics g = new Graphics(result);
    g.setColor(Color.BLACK);
    int xPos = 0;
    int yPos = Display.getHeight() >> 1;
    for (int i = startFrom; i < buffer.length; i += 2 * zoom) {
        byte[] b = new byte[] { buffer[i], buffer[i + 1] };
        int level = (signedShortToInt(b) * 100 / 32767);
        if (100 < level) {
            level -= 200;
        }

        g.drawPoint(xPos, yPos - level);
        xPos++;
    }
    return result;
}

public static final int signedShortToInt(byte[] b) {
    int result = (b[0] & 0xff) | (b[1] & 0xff) << 8;
    return result;
}

屏幕类：

class Scr extends MainScreen {
    BitmapField mGraphField = new BitmapField(new Bitmap(Display.getWidth(),
            Display.getHeight()));

    private VoiceNotesRecorderThread m_thread;

    public Scr() {
        add(mGraphField);
        add(new NullField(FOCUSABLE));
    }

    boolean mRecording = false;
    private int mZoom = 1;
    private int mStartFrom = 0;

    byte[] mAudioData = null;

    protected void makeMenu(Menu menu, int instance) {
        super.makeMenu(menu, instance);
        menu.add(mRecordStopMenuItem);

        menu.add(mPaintZoomIn);
        menu.add(mPaintZoomOut);
        menu.add(mPaintZoomToFitScreen);

        menu.add(mPaintMoveRight);
        menu.add(mPaintMoveLeft);
        menu.add(mPaintMoveToBegin);
    }

    MenuItem mRecordStopMenuItem = new MenuItem("Record", 0, 0) {
        public void run() {
            if (!mRecording) {
                m_thread = new VoiceNotesRecorderThread();
                m_thread.start();
                mRecording = true;
                this.setText("Stop");
            } else {
                m_thread.stop();
                mAudioData = m_thread.getData();
                zoomToFitScreen();
                mRecording = false;
                this.setText("Record");
            }
        }
    };

    MenuItem mPaintZoomIn = new MenuItem("Zoom In", 0, 0) {
        public void run() {
            zoomIn();
        }
    };

    MenuItem mPaintZoomOut = new MenuItem("Zoom Out", 0, 0) {
        public void run() {
            zoomOut();
        }
    };

    MenuItem mPaintZoomToFitScreen = new MenuItem("Fit Screen", 0, 0) {
        public void run() {
            zoomToFitScreen();
        }
    };

    MenuItem mPaintMoveLeft = new MenuItem("Left", 0, 0) {
        public void run() {
            moveLeft();
        }
    };

    MenuItem mPaintMoveRight = new MenuItem("Right", 0, 0) {
        public void run() {
            moveRight();
        }
    };

    MenuItem mPaintMoveToBegin = new MenuItem("To Begin", 0, 0) {
        public void run() {
            moveToBegin();
        }
    };

    private void zoomOut() {
        if (mZoom < 200)
            mZoom++;
        mGraphField.setBitmap(getGraph(mAudioData, mZoom, mStartFrom));
    }

    private void zoomIn() {
        if (mZoom > 1)
            mZoom--;
        mGraphField.setBitmap(getGraph(mAudioData, mZoom, mStartFrom));
    }

    private void zoomToFitScreen() {
        int lenght = mAudioData.length;
        mZoom = (lenght / 2) / Display.getWidth();
        mGraphField.setBitmap(getGraph(mAudioData, mZoom, mStartFrom));
    }

    private void moveRight() {
        if (mStartFrom < mAudioData.length - 30)
            mStartFrom += 30;
        mGraphField.setBitmap(getGraph(mAudioData, mZoom, mStartFrom));
    }

    private void moveLeft() {
        if (mStartFrom > 30)
            mStartFrom -= 30;
        mGraphField.setBitmap(getGraph(mAudioData, mZoom, mStartFrom));
    }

    private void moveToBegin() {
        mStartFrom = 0;
        mGraphField.setBitmap(getGraph(mAudioData, mZoom, mStartFrom));
    }

    protected boolean navigationMovement(int dx, int dy, int status, 
        int time) {

        if (dx < 0) {
            moveLeft();
        } else if (dx > 0) {
            moveRight();
        }
        if (dy < 0) {
            zoomIn();
        } else if (dy > 0) {
            zoomOut();
        }
        return super.navigationMovement(dx, dy, status, time);
    }
}

很有帮助：
ADC ->整数 PCM 文件 ->信号处理
SO - 音频如何用数字表示？
将字节数组转换为整数

Answer 2

在大多数设备中，仅支持单轨 MID 格式。这是 mid0 格式，支持单个轨道中的多种乐器。我不确定 api 是否提供了测量信号幅度的功能。要将 mid 文件转换为您可以使用 Anvil Studio，它有免费版和专业版

要录制音频，您需要使用 Manager.createPlayer("capture://audio")。还将编码（PCM 或 AMR）留给设备实现，因为有些手机不支持 PCM/AMR

希望这会有所帮助！