a) Filter that passes frequencies below a specific frequency.

b) A filter specifically designed to remove frequencies above the cutoff frequency, and allow those below to pass unprocessed is called a lowpass filter. The effect of a lowpass filter is to reduce the amplitude of high frequencies. Common examples include the “treble” controls on many lower end radios and stereos, the passive “tone” controls often found on electric guitars and basses, hi-cut filters on consoles, and of course, this type of filter is found on many synthesizers.