Swing Hacks

Show Audio Information While Playing Sound #77

Chapter 10, Audio

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395

HACK

Testing It Out

Launch the DataLineGUI application and you’ll get a file-selection dialog.

Choose a suitable AIFF or WAV, and you’ll see the GUI shown in

Figure 10-8.

This is all well and good for a simple GUI, but there’s one problem: where

the heck is our level meter?! It should be between the filename and the text

area, but it’s totally not there!

Initially, I suspected my repaint code was hosed, but it all seemed correct.

So, right after figuring out the meter width, I added a sanity-check debug

line:

System.out.println ("level = " + level);

And when I ran it, I got a result that I really didn’t want to see:

[aeris:HacksBook/Media/x11] cadamson% java DataLineInfoGUI

got PCM format

got info

got line

opened line

level = 0.0

level = 0.0

level = 0.0

level = 0.0

level = 0.0

And that was on a really loud song, so it wasn’t just a slow fade in. I looked

around to see if there was something special you have to do for

getLevel( )

to work, but there wasn’t.

Figure 10-8. Audio player display with format information

396

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Chapter 10, Audio

#77 Show Audio Information While Playing Sound

HACK

Then I Googled, and found this post to the javasound-interest mailing list

from February 2003:

Date: Mon, 17 Feb 2003 22:31:21 -0800

Reply-To: Discussion list for JavaSound API

<[e-mail]>

Sender: Discussion list for JavaSound API

<[e-mail]>

From: Florian Bomers <[e-mail]>

Organization: Sun Microsystems Inc.

Subject: Re: DataLine.getLevel( )?

Comments: To: [e-mail]

Content-Type: text/plain; charset=us-ascii

Unfortunately, it is not implemented. (actually, in my private opinion, it

is a questionable method anyway: usually soundcard drivers do not provide

such a primitive, so the Java Sound implementation has to calculate this

"level" on its own. But there are many different algorithms to do so, suited

depending for what the "level" is needed for, and it would possibly eat

unnecessarily processor resources. So I guess it's best if everybody does

the calculation of the "level" on his own on the buffers received by the TDL

or written to the SDL, respectively. Easy and fast algorithms are maximum,

moving average,block average, power).

sorry...

Florian

Knute Johnson wrote:

>

> Anybody know if DataLine.getLevel( ) is implemented? All I get is 0.0

> on SourceDataLines and -1.0 on TargetDataLines.

>

> Thanks,

>

> Knute Johnson

In fact, a little further research shows that the fact that DataLine.getLevel( )

always returns UNKNOWN_LEVEL was filed as bug 4297101 in the Java Bug

Parade on December 6, 1999. Five years later, it’s still not fixed, though it

looks like there was at least an attempt to fix it for Tiger (J2SE 5.0)—a fix

that was abandoned in August 2003.

By the way, wouldn’t it have saved a lot of people a lot of

time if they disclosed in the Javadoc that this method is a no-

op? But I digress….

So, the level meter is not going to work—not because of the graphics, but

because there’s no way to get an accurate level. Or is there?