java - 频率音调发生器播放错误的声音

Question

我在生成特定频率的声音时遇到了一些问题。我已经设置了我的应用程序，因此您可以在搜索栏上来回滑动以选择特定频率，然后该应用程序应使用该频率来生成音调。

我目前听到的音调很好，但它的频率与您设置的频率完全不同。 (而且我知道问题不在于将值从搜索栏传递到“音调生成过程”，所以它一定是我生成音调的方式。)

这段代码有什么问题？谢谢

private final int duration = 3; // seconds
 private final int sampleRate = 8000;
 private final int numSamples = duration * sampleRate;
 private final double sample[] = new double[numSamples];
 double dbFreq = 0; // I assign the frequency to this double
 private final byte generatedSnd[] = new byte[2 * numSamples];

 ...


    void genTone(double dbFreq){

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

        // convert to 16 bit pcm sound array
        // assumes the sample buffer is normalised.
        int idx = 0;
        for (final double dVal : sample) {
            // scale to maximum amplitude
            final short val = (short) ((dVal * 32767));
            // 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_CONFIGURATION_MONO,
                AudioFormat.ENCODING_PCM_16BIT, numSamples,
                AudioTrack.MODE_STATIC);
        audioTrack.write(generatedSnd, 0, generatedSnd.length);
        audioTrack.play();
   }

Answer 1

您的代码实际上是正确的但是看看Sampling theorem .

简而言之:您必须将采样率设置为高于 2*max_frequency。因此，设置 sampleRate = 44000，您应该可以正确听到更高的频率。