Final Cut Pro: What is a Compressor or Limiter Filter

The compressor or limited filter decreases the sound volume above amplitude entry point. This is extremely useful, as it minimizes the difference in volumes of two or more subjects talking. It also ensures that the audio clips fit within playback device limits.

What Is the Compressor or Limited Filter?

The compressor filter is extremely important, as most environments such as movie theaters, televisions and home stereo systems must compete with different levels of ambient noise. This must be conquered by using the absolute quietest sounds within the mix. This filter, when used in Final Cut Pro, allows for the adjustment of the audio clip range so the loudest sections of the audio clip are reduced, while the quietest sections are left the same.

Controls of the Compressor/Limited Filter

The compressor or limited filter has four different controls that can be used to optimize noise level in audio tracks.

  • Ratio Control: This function determines how much compression must be applied to the audio clip. Too much compression gives the audio clip an unvarying, flat signal; less can be more.
  • Threshold Control: This function identifies how loud a signal must be before applying the compression filter; this control is the most important of the five that need to be adjusted.
  • Attack Time: This function identifies how quickly the compression filter responds to the changes in audio volume.
  • Release Time: This function identifies how slowly the compression filter releases the volume change.

The Function of the Compressor/Limited Filter

This process significantly reduces the overall audio volume.  The "Preserve Volume" function takes care of this problem, although the end result is the audio itself being too loud. The "attack time" refers to the timeframe in which this filter decreases the audio volume once it detects an amplitude frequency above its ceiling. The "release time" describes the actual time it takes for the filter to increase audio volume when the high amplitude frequency is done playing. The higher the value, a less noticeable and smoother response is produced. If they are set too high the compressor will not respond as quickly as it should. Unfortunately, this has been adapted from the concept of mixing live audio. One never knows what will come next. By setting the threshold slightly under the preferred limit, the compressor is given more time to decrease the volume in preparation for loud volumes once its threshold has been reached.

A ratio setting indicates to the compressor how much the volume should be reduced when sound goes above and beyond the threshold. For example, if a ratio setting is at a 2:1 ratio, then the volume will only increase by half the dB above the threshold. Also, the compressor filter will lower the sound volume beyond the threshold although this does not necessarily reduce it to a set value below or at its threshold. Take heed that extremely loud sounds could essentially peak.

The compressor also reduces the difference in volume between any background noise and the subject. Therefore, background noise will be essentially more noticeable when increasing the audio once the compressor is applied to the audio tracks.

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