Low/Highpass

Menu Command: Effect | Filter | Low/Highpass

Lowpass filters block high pitched frequencies (treble), but allow low pitched frequencies (bass) to pass. They can be used to reduce high end hiss noise or remove unwanted sounds above the given cutoff frequency. If you were to apply a lowpass filter with a cutoff frequency of 1000Hz on speech, it would make it sound mumbled and deep. Lowpass filters can also be used to eliminate aliasing when used before downsampling.

Highpass filters block low pitched frequencies, but allow high pitched frequencies to pass. They can remove deep rumbling noise or remove unwanted sounds below the given cutoff frequency. If you were to apply a highpass filter with a cutoff frequency of 1000Hz on speech, it would make it sound thin and hollow.

Cutoff frequency
The Initial cutoff box specifies the constant cutoff frequency for static filtering or the initial cutoff frequency for dynamic filtering. If the Dynamic option is selected (see below), then a final cutoff frequency must be given in the Final cutoff box.


Select Lowpass if you want to keep only the frequencies below the cutoff frequency. Select Highpass if you want to keep only the frequencies above the cutoff frequency.

If you want the cutoff frequency to remain constant throughout the selection during processing, select the Static option. If you want the cutoff frequency to change from the initial value to the final value, select the Dynamic option. Note that dynamic filtering will take more processing time.

The Steepness value specifies how sharply the filter cuts off frequencies outside the cutoff frequency. A higher steepness makes the filter sharper, but it also increases processing time. In technical terms, the steepness specifies the number of second order cascade filters used.

Examples
To make speech gradually become more hollow and thin:

  1. Enter 60 in the Initial cutoff box.
  2. Choose Dynamic.
  3. Enter 1000 in the Final cutoff box.
  4. Choose Highpass.
  5. Choose OK.

Filtering before downsampling from 44100Hz to 22050Hz:

  1. Enter 11025 in the Initial cutoff box.
  2. Choose Lowpass.
  3. Choose Static.
  4. Enter 20 in the Steepness box.
  5. Choose OK.

See Also