If a vocal recording has a combination of loud and quiet voices, use the Compressor effect to even out the levels before making major adjustments to the overall volume. Compression reduces the loud sections so that they can match more closely with the quieter ones. After Compressor is applied, the volume of the clips can be increased with Amplify.

1. Playback the quiet portion of the clip, such as a presenter with a quieter voice, to determine the average volume level decibel. Keep this level in mind for step 4a.
2. Select the desired clip(s) for the Compressor effect.
   

• For a single clip, click the top of the clip (near the clip name).

• For multiple clips, click-and-drag to highlight the desired clips with the Selection Tool.

Navigate to Effect > Compressor. A new window will appear.

Adjust the Compressor settings.

• Threshold: The level above which compression is applied. Set the threshold properly to compress loud parts of the audio in order to even-out the levels.
• Noise Floor: Sounds under the Noise Floor limit are considered background, and are not amplified. Something around -50dB is sufficient, but may vary depending on how loud the recording environment was.
• Ratio: Relative amount of compression, compared to the threshold. A 6:1 ratio is the recommended ratio to start with.
• Attack Time: How soon the compressor starts to compress a volume change. .5 seconds is recommended.
• Release Time: How soon the compressor releases the volume change. 1.0 seconds is recommended.
• Make-up gain for 0db after compressing and Compress based on Peaks: Both options should be un-checked. Selecting these options will cause the track to be too loud. To increase overall volume, use the Amplify effect instead.
  
  

Click the "Preview" button to listen to a preview of the effect.

Click "OK."

The waveform should now look mostly even (no really tall sections). If not, undo the effect (Edit > Undo), re-open Compressor, and adjust the settings. After Compressor has been applied, increase the volume of the overall track with Amplify (see Audacity: Increasing Clip Volume (Amplify) for more details).