What determines the steepness?

Filter order determines roll-off steepness. First-order (RC, RL) gives -20 dB/decade. Second-order (LC) gives -40 dB/decade. Higher orders require cascading or active filter designs.

How do I choose component values?

Start with the desired fc. Choose a convenient R (typically 1k-100k for signal filters), then C = 1/(2πRfc). Or choose C first and calculate R. Standard component values may shift fc slightly.

Does a high pass filter affect DC?

No. A high pass filter blocks DC completely. Only frequencies above fc pass through. This is why high pass filters are used for audio coupling and DC blocking.

High Pass Filter Calculator

Passes high frequencies

Attenuates low frequencies

−3 dB at f_c

RC High Pass Filter

Ω Resistance

C Capacitance

Enter component values

High Pass Filter Results

Cutoff fc
—
Hz

ω_c

—

rad/s

Roll-off

—

Gain at 10×f_c

—

Gain at 100×f_c

—

Time Constant

—

Figure 1: A high pass filter passes frequencies above f_c and progressively attenuates frequencies below it. The transition steepness depends on filter order.

Table of Contents

Fundamentals

What Is a High Pass Filter?
How It Works

Worked Examples

Audio AC Coupling
Removing 50Hz Hum

Deep Dive

DC Blocking Applications
Phase Response

Reference

Frequently Asked Questions
Related Filter Calculators

What Is a High Pass Filter?

A high pass filter passes frequencies above its cutoff frequency and attenuates frequencies below it. It is used for DC blocking, bass removal, AC coupling between amplifier stages, and removing low-frequency noise. The Filter Cutoff Frequency Calculator covers the fundamental cutoff frequency calculation that defines every high pass filter.

How It Works

High Pass Filter: f_c = −3 dB point where output power drops to 50%.
Below f_c: stopband | Above f_c: passband

The filter response is determined by the component values and circuit topology. First-order filters (single RC or RL) give −20 dB/decade roll-off. Second-order (LC or cascaded) give −40 dB/decade. The RC Filter Calculator shows how different component combinations affect the response.

Worked Example — Audio AC Coupling

Given: R = 10 kΩ, C = 100 nF

f_c = 1/(2π × 10000 × 100×10⁻⁹) = 159.2 Hz

Frequencies above 159 Hz pass; below are attenuated.

The RL Filter Calculator designs the complementary response.

Worked Example — Removing 50Hz Hum

Given: R = 1 kΩ, C = 1 µF

f_c = 1/(2π × 1000 × 10⁻⁶) = 159.2 Hz

DC Blocking Applications

High-pass filters block DC while passing AC — essential for coupling between amplifier stages and removing offset voltages. The LC Filter Calculator handles the complementary filter type.

Phase Response

Phase response matters in audio and control systems. A first-order filter shifts phase by 45° at fc and approaches 90° at high frequencies. The Low Pass Filter Calculator covers the active version with op-amp gain.

Capacitor Impedance Calculator: At low frequencies capacitors have high impedance and block the signal — the Capacitor Impedance Calculator explores this.

Frequently Asked Questions

What is the −3 dB point?

−3 dB is where the output power is half the input power (voltage is 70.7% of input). This is the universally agreed definition of cutoff frequency for all filter types.

Can I use this for audio?

Yes. Audio frequencies range from 20 Hz to 20 kHz. Choose component values that place f_c within this range for audio filtering applications.

What order filter do I need?

First-order (−20 dB/dec) is adequate for gentle roll-off. For sharper transitions, use second-order (−40 dB/dec) or higher. The Butterworth Filter Calculator designs multi-order responses.

Does the filter introduce delay?

Yes. All filters introduce phase shift and group delay. First-order filters have constant group delay (linear phase approximation). Higher-order filters can have significant group delay variation near fc.

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Last updated: March 2026