Analyse the amplitude while recording a sound


S

Sélénissime

Hello
I would like to record a sound (from the microphone) and, at the same
time, be able to analyse the sound amplitude.
For example, I want to be able to display (in real time) a number
indicating how high is the volume recorded from microphone.

I've looked at javax.sound.sampled API. I could read bytes from the
input Stream, by the method TargetDataLine.read, but I don't how I
could analyse these bytes.
I've looked at JMF API, but it doesn't seem to do what I want.

Thank you in advance for your help
 
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K

Knute Johnson

Hello
I would like to record a sound (from the microphone) and, at the same
time, be able to analyse the sound amplitude.
For example, I want to be able to display (in real time) a number
indicating how high is the volume recorded from microphone.

I've looked at javax.sound.sampled API. I could read bytes from the
input Stream, by the method TargetDataLine.read, but I don't how I
could analyse these bytes.
I've looked at JMF API, but it doesn't seem to do what I want.

Thank you in advance for your help

Cedric:

That's actually pretty easy if you know the format of the audio data.
If the data for example were encoded PCM_UNSIGNED in 8 bit you could
just use the 8 bit value directly. If it is 16 bit signed you would
need to read two bytes and convert it to a short or int value. With PCM
encoding the value of the data is the volume.

Here are the beginnings of some code I wrote to display the peak values.
It is configured for PCM_SIGNED 16 bit audio data. Pass it the byte
buffer that you used to read the data from the TargetDataLine and the
number of bytes of data in the buffer.

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;

public class PeakMeter extends JPanel {
volatile int peak;
volatile double previousLevel;

public void draw(byte[] b, int len) {
int n = 0;

peak = 0;
for (int i=0; i<len; i+=2) {
n = Math.abs((b << 8) | b[i+1]);
if (n > peak)
peak = n;
}
repaint();
}

public void paintComponent(Graphics g2d) {
Graphics2D g = (Graphics2D)g2d;
g.rotate(Math.PI,getWidth()/2,getHeight()/2);

double level = peak / 32768.0;
if (level < previousLevel)
level = previousLevel * 0.80;
previousLevel = level;

g.setColor(Color.WHITE);
g.fillRect(0,0,getWidth(),getHeight());

g.setColor(Color.GREEN);
int h = Math.min((int)(level * getHeight()),(int)(0.70 *
getHeight()));
g.fillRect(0,0,getWidth(),h);

if (level > 0.70) {
g.setColor(Color.YELLOW);
h = Math.min((int)((level - 0.70) * getHeight()),
(int)(0.20 * getHeight()));
g.fillRect(0,(int)(0.70 * getHeight()),getWidth(),h);
}

if (level > 0.90) {
g.setColor(Color.RED);
h = (int)((level - 0.90) * getHeight());
g.fillRect(0,(int)(0.90 * getHeight()),getWidth(),h);
}
}
}
 
A

Andrew Thompson

...I want to be able to display (in real time) a number
indicating how high is the volume recorded from microphone.

I think that what you are asking for is the RMS volume.

I implement an RMS volume for Tracker. E.G.
<http://pscode.org/tracker/applet.html?media.url=/media
%2FDead_End.mp3&media.load=on&media.play=on>

You can 'cancel' the digitally signed code and it
will work equally well (or poorly, depending on
how you look at it).

Note that an RMS volume can only be calculated for
a group of signal samples, so there is always some
lag. The amplitude is calculated for the group of
samples currently plotted. The group of samples,
in turn, is obtained half from the sound just played,
and half from sound about to be played. Of course
that is not an option for analysing sound coming from
a microphone.

In any case, the method I use presumes the signal
has been resolved to a doubles ranging from -1 to 1
(see Knute's code for converting samples to numbers)
and can be seen here
<http://pscode.org/javadoc/src-html/org/pscode/ui/audiotrace/
AudioPlotPanel.html#line.996>
 
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S

Sélénissime

Thank you very much! It is exactly what I wanted.
I didn't think that it would so easy to analyse the volume from an
array of bytes.
 

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