Question

我正在为大学项目创建一个小型听力测试应用程序。我一直在使用以下代码： Playing an arbitrary tone with Android

到目前为止，我有一个带有switch语句的按钮，因此每次单击它时，它都会播放频率增加的音调。然而，当它达到4000Hz时声音将不再播放，有没有人有任何想法？谢谢！

公共类AutoTest扩展了MainActivity {

private final int duration = 5; // seconds
private final int sampleRate = 8000;
private final int numSamples = duration * sampleRate;
private final double sample[] = new double[numSamples];
private  double freqOfTone = 250; // hz
private int inc=0;
int count = 0;

private final byte generatedSnd[] = new byte[2 * numSamples];

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.content_auto_test);
}


 void genTone(){
    // fill out the array
    for (int i = 0; i < numSamples; ++i) {
      //  sample[i] = Math.sin(2 * Math.PI * i / (sampleRate/(freqOfTone+inc)));
        sample[i] = Math.sin((freqOfTone+inc) * 2 * Math.PI * i / (sampleRate));
    }

    // convert to 16 bit pcm sound array
    // assumes the sample buffer is normalised.
    int idx = 0;
    int ramp = numSamples / 20;

    for (int i = 0; i < ramp; i++) {
        // scale to maximum amplitude
        final short val = (short) ((sample[i] * 32767) * i / ramp);
        // in 16 bit wav PCM, first byte is the low order byte
        generatedSnd[idx++] = (byte) (val & 0x00ff);
        generatedSnd[idx++] = (byte) ((val & 0xff00) >>> 8);
    }

    for (int i = ramp; i < numSamples - ramp; i++) {
        // scale to maximum amplitude
        final short val = (short) ((sample[i] * 32767));
        // in 16 bit wav PCM, first byte is the low order byte
        generatedSnd[idx++] = (byte) (val & 0x00ff);
        generatedSnd[idx++] = (byte) ((val & 0xff00) >>> 8);
    }

    for (int i = numSamples - ramp; i < numSamples; i++) {
        // scale to maximum amplitude
        final short val = (short) ((sample[i] * 32767) * (numSamples - i) / ramp);
        // in 16 bit wav PCM, first byte is the low order byte
        generatedSnd[idx++] = (byte) (val & 0x00ff);
        generatedSnd[idx++] = (byte) ((val & 0xff00) >>> 8);

    }
}

void playSound(){
    final AudioTrack audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC,
            sampleRate, AudioFormat.CHANNEL_OUT_MONO,
            AudioFormat.ENCODING_PCM_16BIT, generatedSnd.length,
            AudioTrack.MODE_STREAM);
    audioTrack.write(generatedSnd, 0, generatedSnd.length);
    audioTrack.play();
}

public void playTone(View view)

{

    //switch statement - auto - increment
    switch(count) {
        case 0:
            break;
        case 1:
            inc+=250;
            break;
        case 2:
            inc+=500;
            break;
        case 3:
            inc+=1000;
            break;

        case 4:
            inc+=2000;
            break;
        case 5:
            inc+=2000;
            break;
        case 6:
            inc+=2000;
            break;


        default:
            Log.d("Values","error message");
            break;
    }
    genTone();
    playSound();
    Log.d("Values","This is the value of count"+ count);
    count++;

这是我的代码，我非常感谢任何帮助！

Answer 1

您的采样率为8 kHz -

private final int sampleRate = 8000;

由于采样定理，sample-rate/2以上的所有频率都将开始混叠。这意味着在4000赫兹时你实际听到0赫兹。在4001赫兹，你听到1赫兹。等等。如果您对将来学习更多信号处理感兴趣，请访问维基页面： Wikipedia - Aliasing

尝试将采样率更改为更高的采样率（标准44.1 kHz），这应该可以解决它！

创建听力通过音调生成测试Android应用程序

1 个答案: