Sound recorded under 0 dB

Special Interest Groups Audio Processing
1

Hi,
As far as I remember, the internal microphone of my laptop never worked. But I gave it a test again earlier today, and it seems to be now working!
However, when I record it with Audacity, the waveforms are centred around a negative number, and not around zero, as you can see here:
underzero.png
If I use the “Amplify” effect, the sound is naturally scaled using zero as reference and the sound is moved even more to the bottom.
Is there a way to shift a track vertically in order to centre it? (or to get my mic to work properly?)

Thank you! :slight_smile:
~ nicolas

2

You have significant DC offset on your signal

Use Normalize rather than Amplify as it has an option to remove the DC offset - see: http://manual.audacityteam.org/o/man/normalize.html

WC

3

The internal mics of most laptops cost a few pennies to make.

If you have a problem it is better to post to the Windows, Mac or Linux forum so we know what operating system you have (see the pink panel at the top of this page).

If you are on Windows Vista or later, there is usually a DC offset cancellation control that might help. To check for or enable this:

  • Right-click over the speaker icon in the System Tray > Recording Devices, or click Start > Control Panel > Hardware and Sound > Sound, then the “Recording” tab
  • Right-click over empty space, show disabled and disconnected devices, then right-click over each device and enable it
  • Right-click or select each device, choose “Properties” then look in the “Enhancements” tab
  • If there is no “Enhancements” tab, look in the sound device’s own control panel in “Hardware and Sound”.

Gale

4

Thank you, Normalise was exactly what I was looking for! :slight_smile:
I’ll be using this for future recordings with this mic.

(I’m using Linux, but didn’t though that was OS-related.
Maybe it’s even electrical?)