A) philtre that passes frequencies below a specific frequency.

b) A philtre 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 philtre 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 philtres on consoles, and of course, this type of philtre is found on many synthesizers.