Basic Low-Pass RC Filters

A low-pass filter passes low frequencies and blocks high frequencies.

The filter only allows low frequency signals from 0Hz to its cut-off frequency, ƒc point to pass while blocking those any higher.

Examples of low-pass filters occur in acoustics, optics and electronics.

In an electronic low-pass RC filter for voltage signals, high frequencies in the input signal are attenuated, but the filter has little attenuation below the cutoff frequency 

Electronic low-pass filters are used on inputs to subwoofers and other types of loudspeakers, to block high pitches that they cannot efficiently reproduce. 

Radio transmitters use low-pass filters to block harmonic emissions that might interfere with other communications. 

The tone knob on many electric guitars is a low-pass filter used to reduce the amount of treble in the sound.

Low-pass filters also play a significant role in the sculpting of sound created by analogue and virtual analogue synthesisers

Passive filters are made up of passive components such as resistors, capacitors and inductors and have no amplifying elements (transistors, op-amps, etc) so have no signal gain, therefore their output level is always less than the input.

To create a passive low-pass filter, we need a circuit that consists of a resistor and either a capacitor or an inductor. 

• The cutoff frequency of a low-pass filter indicates the frequency region in which the filter is transitioning from low attenuation to significant attenuation.

The upper cutoff frequency for an RC low pass filter is determined by the circuit resistor and capacitor values. By using the Formula,

ƒc = Cutoff frequency

R = Resistance in Ohms

C= Capacitance in Farads