Dumb question

tvz · Post by **tvz** » Wed Sep 12, 2007 9:47 pm

Here's the dumbest question ever--What does the vertical axis in the basic screen indicate? It doesn't seem to be volume, is it?

DougDbug · Post by **DougDbug** » Thu Sep 13, 2007 2:29 pm

Well... it's sort-of volume....

It's shows the amplitude* of the waveform. If you zoom-in, you can see the actual waveform... In the default view, the waves are too squished-together to see the individual waves.

Waves go positive and negative. Big waves are loud, small waves are quiet. Silence is a straight line down the center. The loudest sounds go all the way positive and all the way negative.

Here's something you can try -
- Open a WAV file
- Select the entire file
- Click Effect -> Volume -> Change
- Change the volume by -12dB and observe the display.
- (Undo the change, if you want...)

If you really zoom-in you will see that the waveform is made-up of small straight lines. The digital wave form is made-up of individual samples. In the case of CD audio, there are 44,000 samples per second. (That's why you have to zoom-in so far to see the wave.) When you "connect the dots" (connect the samples) you get a waveform.

Note that decibels are usually referenced to the maximum level. Zero dB represents the maximum level, and this is 100% on the GoldWave default display -6dB is half of full-scale. The smallest wave you can make with 16-bits is something like -93dB or -96dB ... I can't remember exactly... Absolute silence is "minus infinity" dB. You can put absolute silence into a 16-bit file, but you can't represent anything in-between... You can't have -100dB in a 16-bit file...

* Sometimes this type of (zoomed-out) display is called the waveform envelope. It's like an outline around the waveform... The waveform fits (tightly) inside the envelope... Sort-of like a rubber envelope, I guess.

tvz · Post by **tvz** » Fri Sep 14, 2007 8:32 am

Wow, that was quite an explanation, Doug. Thanks.

What puzzles me is the fact that when I maximize volume, I've noticed that the "current maximum" given does not appear to correspond to the longest verical lines on the graph. Shouldn't it?

DougDbug · Post by **DougDbug** » Fri Sep 14, 2007 3:21 pm

Yeah, I would think so... Did you zoom in at the reported maximum?

The same maximum level might exist more at than one place in the file... This is very likly to be the case with a file ripped from a CD, because it might have already been maximized (and compressed & peak-limited).

I assume the reported current maximum point is the first one. ... Maybe it's very brief and it doesn't show-up 'till you zoom????

...I just took a look at a short WAV file on my system. The current maximum point did seem to be where the biggest waves are, in this particular file.

donrandall · Post by **donrandall** » Tue Sep 18, 2007 1:00 am

I've noticed that when zoomed out to look at the entire track, it often occurs that there does not appear to be any instance of the wav reaching (or exceeding) 0db. Running "Maximize Volume" may reveal that 0db has been reached (or exceeded) and if so, it tells the precise point(s) at which this occurred. Upon zooming in to inspect the wav at the indicated point, I may discover that it most certainly is maxed out - even thought it did not appear so while viewing the entire file or even a very large portion of the file.

Because of that, I ALWAYS make it a point to run "Maximize Volume" before saving to be sure just exactly what's going on.