Input filter for recording

I’ve noticed on at least a couple computers (with onboard sound, not better sound cards) that when the waveform view goes down to -36dB or lower (-48, -60, etc.), I’m seeing a DC offset on the quiet portions (the louder parts make it invisible). Unplugging the source from the line-in makes no difference on this offset, so the DC is internal to the board.

Is there any input filter plugin available for Audacity to get rid of this offset between the sound card and the program? All I need is a subsonic filter, though I suppose some might want more bands of equalization. I know I can apply a filter after recording but I was hoping to filter first.

input filter plugin

No. Audacity doesn’t do anything in real time.
This is a feature request.

If you’re on Vista or Windows 7:
Right-click over the Speaker icon by the system clock then choose Recording Devices to open the Recording tab of “Sound”.
Right-click over Microphone and choose Properties.
There will probably be an Enhancements tab.
If there is, look for an option for “DC offset correction” (or something along those lines. If this option exists, select it. Note that all other Enhancements should be switched of for recording.

No, I’m still using XP. And I said line-in, not mic-in.

Using a new computer (Win 10) and USB sound card, I’m seeing the same (worse) DC offset, this time not affected by the input volume control like the old one was. Is there any change in the availability of input filters? All I should need is a subsonic filter.

Check the settings for the recording device in the Windows Sound control panel. Windows often provides a DC blocking / subsonic filter.

And I said line-in, not mic-in.

Windows treats everything as a microphone. They probably thought that was easier than trying to explain the difference.

Is there any change in the availability of input filters?

It’s not an “input filter” problem. Audacity, by conscious design doesn’t do anything to the sound on recording. In general rule, Macs don’t either. Windows is the one that can apply filters, effects and corrections.

I once got a Windows machine from the Systems people and it wouldn’t pass sound tests. Somebody left Windows “Cathedral Effects” running by accident.