Apple MA261Z/A User Manual - Page 644

Unlike a compressor, which affects the loud parts of a signal, expansion affects the quiet parts of the signal:  Threshold: This slider defines how low the lowest portion of the clip can be before expansion is applied. This is the first setting you'll adjust.  Ratio: This affects how much expansion is applied to boost the signal.  Attack Time: This defines how quickly the filter reacts to changes in volume (the default is usually fine, but you may want to experiment).  Release Time: This defines how slowly the filter lets go of the change in volume it made (the default is usually fine, but you may want to experiment). Noise Reduction Filters Final Cut Express HD has three noise reduction filters for use in specific situations:  Hum Remover  Vocal DeEsser  Vocal DePopper Hum Remover The Hum Remover lets you get rid of "cycle hum" that may have been introduced into your audio recording by power lines crossing your cables, or by a shorted ground wire in your setup. Hum from power sources generally sounds like a low buzzing and has a frequency that corresponds to the electrical power in your country (for example, countries in North America use 60 Hz AC power, while most countries in Europe use 50 Hz power).  Frequency: This slider lets you select the frequency of hum that this filter will attempt to remove. Different countries use different power frequencies, so you need to specify exactly what frequency to tune out. In general, most AC (alternating current) operates at either 50 or 60 Hz.  Q: This slider allows you to select a range of frequencies to filter. If the important elements of your recording overlap into the frequencies that are being filtered out, you might want to narrow this value somewhat. 644 Part VIII Audio Mixing