Cutoff

• The cutoff point of a filter determines the frequency at which the filter starts to reduce the volume of the sound. If, for example, you set a low pass filter's cutoff point to 500 Hertz, the equalizer reduces the volume of all the frequencies above 500 Hertz. Raising the cutoff control lets more high-frequency sound through the EQ; lowering the cutoff control lets less high-frequency sound through, making the audio sound bassier.
  
  

Slope

• The slope of a filter determines how sharply it reduces the volume of the frequencies above the cutoff point. A low slope setting makes the filter gradually reduce the volume, while a high slope setting makes it quickly bring the volume down. If, for example, the cutoff point is set to 500 Hertz, a gentle slope setting would mean that the volume of the 1,000 Hertz point on the frequency spectrum is only somewhat lowered. A steep slope, on the other hand, would reduce the volume of this frequency point drastically. Some equalizers have a dedicated slope control marked in decibels; others use the "Q" control to set the slope.
  
  

Use in Mixing

• When you're mixing the different tracks of a song together, use a low pass filter to eliminate unwanted high frequencies from a track. Applying a low pass filter to a screechy violin, for example, can mellow its sound. If a recorded audio track contains static or other high-frequency interference, use a low pass filter to remove it from the recording. You can also apply a low pass filter to the bass or kick drum track to ensure that any high frequencies on these track don't conflict with the rest of the production.
  
  

Use in Synthesis

• Use the low pass filter on a synthesizer to create bass sounds. Set the cutoff point on the filter fairly low, then increase the slope to add presence and punch. The slope control on a synthesizer's low pass filter is usually marked "Resonance" or "Res." To create a more interesting bass sound, use the synthesizer's envelope or low frequency oscillator to modify the filter's cutoff point, thereby creating a pulsing sense of movement within the sound.