Why does my ad sound different after compressor changes while the curve graph stays the same?

Understand What the Static Curve Represents

Audacity's Compressor reduces dynamic range by controlling the relationship between input and output levels. The compression curve graph represents that level mapping, with input level on the horizontal axis and output level on the vertical axis.

The Development Manual says the graph responds to Threshold, Ratio, Make-Up Gain and Knee Width. Threshold anchors the transition; a wider knee can begin compression before it. Ratio controls the mapping above the threshold. Make-Up Gain applies a shared gain after compression. These curve controls are distinct from timing controls.

The graph does not display every behavior of the compressor. In particular, it does not change when only the smoothing controls are adjusted, even though those controls affect the resulting sound.

A calculated example makes the static mapping concrete: with Threshold -18 dB, Ratio 3:1, Knee Width 0 dB and Make-Up Gain 0 dB, an input at -12 dB is 6 dB above the threshold. The ratio reduces that excess to 2 dB, giving a static mapped output of -16 dB. This is arithmetic for the transfer curve, not a measured output or a prediction of its time-dependent response.

The Development Manual's Compressor description distinguishes the static curve controls from smoothing.

Separate Lookahead, Attack, and Release

The smoothing controls describe how compression develops over time. Lookahead allows compression to begin gradually before the signal crosses the threshold. Attack governs the gradual response after the signal crosses that threshold. Release governs how compression relaxes after the signal falls below it.

These timing behaviors can change the sound of consonants, sudden emphasis, percussion, and the transition between loud and quiet passages without changing the static input-output mapping.

The manual explains that Attack can temporarily allow the output to exceed the target compression mapping, while Release can temporarily produce more compression than the static mapping calls for. These are time-dependent responses, not necessarily errors in the curve.

Decision branch: If the static level relationship is wrong, investigate Threshold, Ratio, Knee Width, or Make-Up Gain. If the static curve is acceptable but transients or transitions sound wrong, investigate Lookahead, Attack, and Release instead.

Illustrative Exercise: Two Inputs, One Curve

Illustrative exercise — hypothetical material, not a product test. Use emphasized narration for A and percussive music for B. On separate copies, hold Threshold, Ratio, Make-Up Gain and Knee Width fixed, then change one smoothing control at a time.

Record the actual parameter values and listening observations in the worksheet. Compare Attack on A and Release or Lookahead on B; listen for consonant clarity, pumping and recovery after transients. No preferred settings or listening results are supplied here.

Validate the Processed Audio, Not Just the Diagram

Version note: the current Compressor manual describes an input-output curve and a realtime metering panel with Input, Output and Compression toggles. The development-manual actual-versus-target display below is not a promise of identical labels in your installed interface. Check the actual version and use the controls it provides.

The Development Manual describes an additional graph in realtime Compressor use. Unlike the static curve, this display can show input, output, actual compression, and target compression. Comparing actual and target compression can help reveal smoothing behavior.

When available in your installed version, use that realtime view as a diagnostic aid. Otherwise, compare processed duplicates while changing only one parameter at a time.

Listen to the complete advertisement at a consistent monitoring level. Check product names, numerical claims, breath sounds, music transients, and the closing call to action. Make-Up Gain can alter output level, so avoid confusing a louder comparison with an automatically better result.

No single Attack, Release, or Lookahead value is appropriate for every advertisement. The cited development documentation establishes control behavior, not universal presets or verified results for a particular commercial recording.

The current Compressor manual describes Input, Output and Compression toggles when Compressor is used as a track effect.

Illustrative Exercise — Static Curve Versus Time-Dependent Response

These are illustrative exercise rows. Save a copy and record your own observations; the example is not an executed acceptance test.

Download review worksheet (CSV)