Compression, Limiting, and Dynamic Range Processing

What You’ll Learn

You’ll learn to use Audacity’s compression and limiting tools to control audio dynamics, reduce volume fluctuations, and create professional-sounding, polished mixes. Compression is fundamental to modern audio production, enabling you to keep quiet sections audible and loud sections controlled without manual volume adjustments.

Key Concepts

Compression reduces the volume of audio when it exceeds a set threshold, with the reduction ratio determining how much the signal is squeezed. The key parameters in Audacity’s Compressor effect are threshold (the level above which compression starts), ratio (how much reduction occurs), attack time (how quickly compression engages), release time (how quickly compression stops), and makeup gain (automatically restoring overall volume after compression). A limiter is a specialized compressor with a very high ratio (typically 10:1 or higher) that acts as a safety ceiling, preventing audio from exceeding a maximum level. Understanding these parameters allows you to transparently tighten sloppy vocals, add cohesion to drums, and protect against digital clipping while maintaining natural-sounding audio.

• Setting the Threshold and Ratio: The Threshold setting (measured in dB) determines at what point compression begins—set it where only the peaks you want to control exceed this level. The Ratio (e.g., 2:1, 4:1, 8:1) defines how much compression occurs; a 4:1 ratio means for every 4 dB above the threshold, only 1 dB comes out, making it ideal for vocal compression without obvious artifacts.
• Attack and Release Timing: Attack time (5-100 milliseconds for vocals, 0-5 milliseconds for drums) controls how fast compression responds to peaks—slower attacks let transients through for natural punch, while fast attacks control peaks immediately. Release time (typically 50-300 milliseconds) determines how quickly compression stops after the signal falls below the threshold; longer releases create smoother, more transparent compression.
• Limiter as a Safety Tool: Set the Compressor to a 10:1 or higher ratio with a fast attack (0-5 ms) to create a limiter that prevents audio from exceeding your threshold level, protecting against unexpected clipping peaks while allowing normal audio to pass through unaffected when it stays below the threshold.
• Makeup Gain for Level Compensation: After compression reduces peak levels, enable and adjust the makeup gain setting to restore the overall output level of your compressed audio, ensuring the signal remains at consistent loudness with your uncompressed tracks for seamless integration into your mix.

Practical Application

Load a vocal track that has inconsistent volume levels, then apply the Compressor effect with a threshold of -20 dB, a ratio of 4:1, attack of 10 ms, and release of 100 ms to even out the dynamics. Listen to the result and adjust the makeup gain so the compressed vocal sits at the same perceived volume as before, creating a controlled, professional sound without obvious “pumping.”