Re: Java silence detection

From:
miraglia.c@gmail.com
Newsgroups:
comp.lang.java.help
Date:
19 Oct 2006 13:41:45 -0700
Message-ID:
<1161290505.079927.169350@m7g2000cwm.googlegroups.com>
Andrew Thompson ha scritto:

miraglia.c@gmail.com wrote:
....

I used a simple mathematic average like this:

if((numBytesRead= targetLine.read(data, 0, bufferLengthInBytes)) ==-1)
{break;}
                    somma=0;
                    for(int i = 800; i<20000; i+=1 ){
                        somma += Math.abs ( data [i]);
                    }

I had been meaning to ask if you had taken the format
of the data line into account. I was surprised to see that
all lines on my PC were stereo 44.1KHz - 16 bit (signed
or something).

When plotting the data, it was apparent I was making
some fundamental mistake in converting the bytes to
numbers, and my traces* 'looked like your description'.

* <http://www.physci.org/test/oscilloscope/screenshots/>
Note particularly the images prefixed with 'sinetone' -
I wanted the simplest of input signals.

Go to the parent directory for the 'audiotraces' Jar file,
the source I of it, and the small 'tone.jar' which I found
handy for testing..

BTW - please remove tab's from source before posting.
2 or four space characters is best.

Andrew T.


No, I hadn't taken in account the format of the data line.

I just read the sound data from the targetDataLine and

converted every single byte (they are 44100) from the line

in a number. I suppose that when this number was near to

0...it was silence. But I discovered that these values are,

in a lot of cases, very far from 0. This is why I introduced

the average.

All lines on my PC are 44.1 KHz 16 bit PCM_SIGNED too (I

found out these infos from your "audiotraces.jar").

I executed your application and I can't understand why

did you write "I was making some fundamental mistake in converting

the bytes to numbers". I think your traces are good. I just

understood that reading from the line produces an array of

byte of 44100 elements. Every one of them is a frequency.

But I am not able to understand nothing about the number of

channels (stereo).

Fortunately for me, I'm not interested in distinguish the

actual signal from noise. I just want to detect silence

to stop recording (acquiring sound data).

I hope my post will be useful for you.

Kar

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