Audacity Forum

Hallo everybody,
i need to change the amplitude of small parts of the signal. I'd like to define the resulting amplitude, say, changing from 85 to 78 dB.
Now, I can't figure out what exactly the figures in Effects... Amplify... stand for. If i increase the numbers, clipping is needed (signal is too loud). if i SLIGHTLY decrease the numbers, the signal gets LOUDER. If i further decrease the numbers i get a softer sound. Why is that?
How can i define the end result exactly? I can't rely on the slider.

Thank you.
keter

We should probably change your timeline from the default into dB, so all the tools match. Black down arrow on the left > Waveform (dB). Stretch your waveform taller to get better accuracy.

It's optional to detach the meters, but that can help, too. View > Float Meter Toolbar.

You should have something that looks like this:

http://kozco.com/tech/audacity/AudacityPanelFull.jpg

Now, if you magnify and select a small portion of the blue waveform, you can apply Effect > Amplify > Amplification dB to cause the waveforms to increase or decrease by the number you type in. -6dB, +10dB, whatever. Plus goes up, minus goes down, and the effect will match the numbers on the left of the waveform.

There are a couple of magic numbers. -6dB or +6dB is half and double the sound signal, but to your ear, it only sounds like a very small change. Your ear hears roughly half-volume at -18dB. This is one reason why percentages don't work well for sound.

Any signal that touches 0dB on either the waveform or the audio meters however briefly, gets damaged. That's called clipping for what it makes the blue waveform look like--tops or bottoms clipped off.

OK, now we're all singing from the same hymnal, what's the question again?

Koz

if i SLIGHTLY decrease the numbers, the signal gets LOUDER. If i further decrease the numbers i get a softer sound. Why is that?

When you first open the "amplify" effect, it analyzes the signal and gives you a default value that will amplify the signal as much as possible without clipping. If you adjust this value slightly down from where it starts, the signal will still be louder in the end since you're starting from the highest possible value.

If you want your signal to peak at a specific value, then set the value you want in the other box labeled "New Peak Amplitude."