我想要从任何Android设备获取超声波,例如频率在18KHz和19KHz之间的超声波。从Android获取超声波使用频率
我使用下面的代码来计算频率,但它似乎并没有得到我正确的频率。我得到的频率停留在11 KHz和13KHz之间。
private void calculateFrequency()
{
// 1 - Initialize audio
int channel_config = AudioFormat.CHANNEL_CONFIGURATION_MONO;
int format = AudioFormat.ENCODING_PCM_16BIT;
int sampleRate = 8000;
int bufferSize = 2048;
if (bufferSize < AudioRecord.getMinBufferSize(sampleRate, channel_config, format))
bufferSize = AudioRecord.getMinBufferSize(sampleRate, channel_config, format);
AudioRecord audioInput = new AudioRecord(AudioSource.MIC, sampleRate, channel_config, format, bufferSize);
// 2 - Get sound
byte[] audioBuffer = new byte[bufferSize];
audioInput.startRecording();
int nbRead = audioInput.read(audioBuffer, 0, bufferSize);
audioInput.stop();
audioInput.release();
// 3 - Transform to double array
double[] micBufferData = new double[bufferSize];
final int bytesPerSample = 2; // As it is 16bit PCM
final double amplification = 100.0; // choose a number as you like
for (int index = 0, floatIndex = 0; index < nbRead - bytesPerSample + 1; index += bytesPerSample, floatIndex++) {
double sample = 0;
for (int b = 0; b < bytesPerSample; b++) {
int v = audioBuffer[index + b];
if (b < bytesPerSample - 1 || bytesPerSample == 1) {
v &= 0xFF;
}
sample += v << (b * 8);
}
double sample32 = amplification * (sample/32768.0);
micBufferData[floatIndex] = sample32;
}
// 4 - Create complex array
Complex[] fftTempArray = new Complex[bufferSize];
for (int i=0; i<bufferSize; i++)
{
fftTempArray[i] = new Complex(micBufferData[i], 0);
}
// 5 - Calculate FFT
Complex[] fftArray = FFT.fft(fftTempArray);
// 6 - Calculate magnitude
double[] magnitude = new double[bufferSize/2];
for (int i = 0; i < (bufferSize/2); i++)
{
magnitude[i] = Math.sqrt(fftArray[i*2].re() * fftArray[i*2].re() + fftArray[i*2].im() * fftArray[i*2].im());
}
// 7 - Get maximum magnitude
double max_magnitude = -1;
for (int i = 0; i < bufferSize/2; i++)
{
if (magnitude[i] > max_magnitude)
{
max_magnitude = magnitude[i];
}
}
// 8 - Calculate frequency
int freq = (int)(max_magnitude * sampleRate/bufferSize);
((TextView) findViewById(R.id.textView1)).setText("FREQUENCY = " + freq + "Hz");
}
我使用两部手机:一个发送超声波与this app,另一个得到这个超声波。 我用这个question作为起始点,我接受了FFT和复杂类。
我的代码有什么问题?
不错的主意。你能否为我解释一下:'int freq =(int)(max_magnitude * sampleRate/bufferSize);'。 – FelixMarcus 2014-10-31 15:59:12
我用这个答案[链接](http://stackoverflow.com/a/7675171/1770833):请参阅代码的最后一行 – Drakkin 2014-10-31 16:02:35
错误在步骤7和8 - 您需要最大量级的*索引*以确定频率,而不是幅度本身。更仔细地看链接答案中的伪代码。 – 2014-11-01 08:37:54