我正在编写一个媒体播放器Android应用程序。
我想使用AudioTrack类，因为我想使用一个超过5个波段的均衡器。
我的问题是，我解码.mp3文件并使用AudioTrack播放示例。这很好用，但是当我使用BiQuad peakEq滤波器时，我的轨道在我想要提升的频率处噼啪作响。
这是我的代码：
Player.java:
public class Player {
private static final String TAG = Player.class.getSimpleName();
public short[] buffer;
public boolean firstStart = false;
public static volatile int position = 0;
public static short[] decode(String path, int startMs, int maxMs)
throws IOException, DecoderException {
short[] pcm = new short[16070400];
int position = 0;
float totalMs = 0;
boolean seeking = true;
File file = new File(path);
InputStream inputStream = new BufferedInputStream(new FileInputStream(
file), (8 * 1024));
try {
Bitstream bitstream = new Bitstream(inputStream);
Decoder decoder = new Decoder();
boolean done = false;
while (!done) {
Header frameHeader = bitstream.readFrame();
if (frameHeader == null) {
done = true;
} else {
totalMs += frameHeader.ms_per_frame();
if (totalMs >= startMs) {
seeking = false;
}
if (!seeking) {
SampleBuffer output = (SampleBuffer) decoder
.decodeFrame(frameHeader, bitstream);
if (output.getSampleFrequency() != 44100
|| output.getChannelCount() != 2) {
throw new DecoderException(
"mono or non-44100 MP3 not supported", null);
}
short[] buffer = output.getBuffer();
for (int i = 0; i < buffer.length; i++) {
pcm[position] = buffer[i];
position++;
}
}
if (totalMs >= (startMs + maxMs)) {
done = true;
}
}
bitstream.closeFrame();
}
Log.i(TAG, "position " + position);
return pcm;
} catch (BitstreamException e) {
throw new IOException("Bitstream error: " + e);
} catch (DecoderException e) {
Log.w(TAG, "Decoder error", e);
throw new DecoderException(maxMs, e);
} finally {
}
}
private void fillBuffer(short[] samples) {
BiQuad filter = new BiQuad(FilterType.PEAK, (63.0 / 44100.0), 0.707, 5.0);
for (int i = 0; i < buffer.length; i++) {
buffer[i] = (short) filter.process(buffer[i]);
}
}
public void playWithAudioTrack() throws IllegalArgumentException,
SecurityException, IllegalStateException, IOException,
DecoderException {
new Thread(new Runnable() {
@Override
public void run() {
try {
String path = "/storage/sdcard0/Music/lordi.mp3";
MediaPlayer mPlayer = new MediaPlayer();
mPlayer.setDataSource(path);
mPlayer.prepare();
int durationMs = mPlayer.getDuration();
if (!firstStart) {
buffer = decode(path, 0, durationMs);
}
fillBuffer(buffer);
int minSize = AudioTrack.getMinBufferSize(44100,
AudioFormat.CHANNEL_OUT_STEREO,
AudioFormat.ENCODING_PCM_16BIT);
AudioTrack track = new AudioTrack(
AudioManager.STREAM_MUSIC, 44100,
AudioFormat.CHANNEL_OUT_STEREO,
AudioFormat.ENCODING_PCM_16BIT, minSize,
AudioTrack.MODE_STREAM);
track.play();
for (int i = 0; i < buffer.length; i++) {
track.write(buffer, i, buffer.length);
}
track.release();
firstStart = true;
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalStateException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// TODO Auto-generated method stub
catch (DecoderException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
}
}
}).start();
}
}
这里是BuQuad.java：
public class BiQuad
{
FilterType filterType;
double a0, a1, a2, b1, b2;
double Fc, Q, peakGain;
double z1, z2;
public enum FilterType
{
LOWPASS,
HIGHPASS,
BANDPASS,
NOTCH,
PEAK,
LOWSHELF,
HIGHSHELF;
};
public float process(float in)
{
double out = in * a0 + z1;
z1 = in * a1 + z2 - b1 * out;
z2 = in * a2 - b2 * out;
return (float)out;
}
public BiQuad()
{
filterType = FilterType.LOWPASS;
a0 = 1.0f;
a1 = a2 = b1 = b2 = 0.0f;
Fc = 0.50f;
Q = 0.707f;
peakGain = 0.0f;
z1 = z2 = 0.0f;
}
public BiQuad(FilterType filterType, double Fc, double Q, double peakGainDB)
{
setBiquad(filterType, Fc, Q, peakGainDB);
z1 = z2 = 0.0f;
}
public void setType(FilterType filterType) {
this.filterType = filterType;
calcBiquad();
}
public void setQ(double Q) {
this.Q = Q;
calcBiquad();
}
public void setFc(double Fc) {
this.Fc = Fc;
calcBiquad();
}
public void setPeakGain(double peakGainDB) {
this.peakGain = peakGainDB;
calcBiquad();
}
public void setBiquad(FilterType filterType, double Fc, double Q, double peakGainDB) {
this.filterType = filterType;
this.Q = Q;
this.Fc = Fc;
setPeakGain(peakGainDB);
}
public void calcBiquad() {
double norm;
double V = Math.pow(10, Math.abs(peakGain) / 20.0);
double K = Math.tan(Math.PI * Fc);
switch (this.filterType) {
case LOWPASS:
norm = 1 / (1 + K / Q + K * K);
a0 = K * K * norm;
a1 = 2 * a0;
a2 = a0;
b1 = 2 * (K * K - 1) * norm;
b2 = (1 - K / Q + K * K) * norm;
break;
case HIGHPASS:
norm = 1 / (1 + K / Q + K * K);
a0 = 1 * norm;
a1 = -2 * a0;
a2 = a0;
b1 = 2 * (K * K - 1) * norm;
b2 = (1 - K / Q + K * K) * norm;
break;
case BANDPASS:
norm = 1 / (1 + K / Q + K * K);
a0 = K / Q * norm;
a1 = 0;
a2 = -a0;
b1 = 2 * (K * K - 1) * norm;
b2 = (1 - K / Q + K * K) * norm;
break;
case NOTCH:
norm = 1 / (1 + K / Q + K * K);
a0 = (1 + K * K) * norm;
a1 = 2 * (K * K - 1) * norm;
a2 = a0;
b1 = a1;
b2 = (1 - K / Q + K * K) * norm;
break;
case PEAK:
if (peakGain >= 0) { // boost
norm = 1 / (1 + 1/Q * K + K * K);
a0 = (1 + V/Q * K + K * K) * norm;
a1 = 2 * (K * K - 1) * norm;
a2 = (1 - V/Q * K + K * K) * norm;
b1 = a1;
b2 = (1 - 1/Q * K + K * K) * norm;
}
else { // cut
norm = 1 / (1 + V/Q * K + K * K);
a0 = (1 + 1/Q * K + K * K) * norm;
a1 = 2 * (K * K - 1) * norm;
a2 = (1 - 1/Q * K + K * K) * norm;
b1 = a1;
b2 = (1 - V/Q * K + K * K) * norm;
}
break;
case LOWSHELF:
if (peakGain >= 0) { // boost
norm = 1 / (1 + Math.sqrt(2.0) * K + K * K);
a0 = (1 + Math.sqrt(2.0*V) * K + V * K * K) * norm;
a1 = 2 * (V * K * K - 1) * norm;
a2 = (1 - Math.sqrt(2.0*V) * K + V * K * K) * norm;
b1 = 2 * (K * K - 1) * norm;
b2 = (1 - Math.sqrt(2.0) * K + K * K) * norm;
}
else { // cut
norm = 1 / (1 + Math.sqrt(2.0*V) * K + V * K * K);
a0 = (1 + Math.sqrt(2.0) * K + K * K) * norm;
a1 = 2 * (K * K - 1) * norm;
a2 = (1 - Math.sqrt(2.0) * K + K * K) * norm;
b1 = 2 * (V * K * K - 1) * norm;
b2 = (1 - Math.sqrt(2.0*V) * K + V * K * K) * norm;
}
break;
case HIGHSHELF:
if (peakGain >= 0) { // boost
norm = 1 / (1 + Math.sqrt(2.0) * K + K * K);
a0 = (V + Math.sqrt(2.0*V) * K + K * K) * norm;
a1 = 2 * (K * K - V) * norm;
a2 = (V - Math.sqrt(2.0*V) * K + K * K) * norm;
b1 = 2 * (K * K - 1) * norm;
b2 = (1 - Math.sqrt(2.0) * K + K * K) * norm;
}
else { // cut
norm = 1 / (V + Math.sqrt(2.0*V) * K + K * K);
a0 = (1 + Math.sqrt(2.0) * K + K * K) * norm;
a1 = 2 * (K * K - 1) * norm;
a2 = (1 - Math.sqrt(2.0) * K + K * K) * norm;
b1 = 2 * (K * K - V) * norm;
b2 = (V - Math.sqrt(2.0*V) * K + K * K) * norm;
}
break;
}
}
}
我不知道问题出在哪里......
我希望有人可以帮助我！
答案 0 :(得分：0)
我没有真正检查后面的数学计算（只是对这个主题不太了解）。我刚刚认识到的是，大多数计算都没有检查值的溢出。 这将以某种方式与你的解释相匹配，它适用于0dB设置和降低放大率。