Audacity Forum

Some audio clips have too-loud signal level so green bars in the playback Meter bounce into red while playing, cause clipping. Is there any difference when adjust the audio track's gain: as the 1st step of editing, via reducing the track's volume by adjusting gain control slider in the track Control Panel, or I can do this this via Normalize effect(the last step of audio editing), which normalize the maximum amplitude to -3dB when applied, then green bar does not exceed 0 dB anymore.

Once a track has been recorded too loud and distorts, that's it, there is a "Clip Fix" effect that may help a little but it is unlikely that there is anything that can be done to fully repair the damage. It is essential that you avoid recording too loud as it can't be fixed later.

sure, but I can no control how the track has been recorded, I just work with ready mp3.
Just want to clarify is there any difference how to adjust the audio track's gain.

You can use the Amplify Effect, or the Normalize effect (from the effects menu) or you can use the track volume slider. All of these will change the track playback level, but if the audio is already clipped they will not "un-distort" the audio, they will just make it play distorted more quietly.

If the MP3 is only slightly clipped, you may be able to recover the track without distortion if you have the Audacity "Quality" settings set to "32 bit" (Edit menu > Preferences > Quality) and then use the "Amplify" effect to lower the volume a little. This will sometimes work due to an anomaly in some MP3 files where the signal goes over 0dB but is not clipped.