我如何生成Java（Android版）正弦扫频 [英] How do I generate a Sine Sweep in Java (Android)

问题描述

我发现播放与Android 任意色调是有帮助的，当我产生频率音。现在我想的频率，而音播放改变。

I found Playing an arbitrary tone with Android to be helpful when I was generating a frequency tone. Now I want the frequency to change while the tone is playing.

我修改了genTone是类似这样的：

I modified the genTone to be similar to this:

private void genTone(double startFreq, double endFreq, int dur) {
    int numSamples = dur * sampleRate;
    sample = new double[numSamples];
    double currentFreq = 0, numerator;
    for (int i = 0; i < numSamples; ++i) {
        numerator = (double) i / (double) numSamples;
        currentFreq = startFreq + (numerator * (endFreq - startFreq));
        if ((i % 1000) == 0) {
            Log.e("Current Freq:", String.format("Freq is:  %f at loop %d of %d", currentFreq, i, numSamples));
        }
        sample[i] = Math.sin(2 * Math.PI * i / (sampleRate / currentFreq));
    }
    convertToPCM(numSamples);
}

private void convertToPCM(int numSamples) {
    // convert to 16 bit pcm sound array
    // assumes the sample buffer is normalised.
    int idx = 0;
    generatedSnd = new byte[2 * numSamples];
    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);

    }
}

日志显示这似乎是为currentFreq正确的值，但是，听语气当归变太高了，太快了。例如，如果我开始在400Hz的去到800HZ，示波器显示它是真正从400Hz的要在同一时间1200Z。

The log shows what appears to be the correct value for currentFreq, however, when listening to the tone the sweep goes too high, and too fast. For example if I start at 400hz and go to 800hz, an oscilloscope shows that it is really going from 400hz to 1200z in the same time.

我不知道我做错了，谁能帮助？

I am not sure what I am doing wrong, can anyone help?

推荐答案

哪个效果没有改变的采样率已经在频率示波器测量的？我会尝试增加采样率到如果可能的话较高的值，因为较高的采样率，越准确所产生的信号就可以了。

Which effect does changing the the samplerate has in the frequency measured by the oscilloscope? I would try to increase the samplerate to higher values if possible, because the higher the samplerate is, the more accurate the generated signal can be.

反正如果开不帮助，请从调整公式：

Anyways if that does't help, please tweak the formula from:

currentFreq = startFreq +（分子*（endFreq - startFreq））;

currentFreq = startFreq + (numerator * (endFreq - startFreq));

到

currentFreq = startFreq +（分子*（endFreq - startFreq）） / 2

currentFreq = startFreq + (numerator * (endFreq - startFreq))/2;

和告诉我们你的信号变化的新的测量间隔了。

and tell us the new measured interval of variation of your signal now.

祝你好运。

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