Filter Configuration
Calculated Components
Enter parameters and click Calculate.
Circuit Diagram
Frequency Response
Learn More About Notch Filters
A notch filter, also known as a band-stop or band-reject filter, is an electronic filter that passes most frequencies unaltered but attenuates a very specific, narrow frequency range to very low levels. It is the opposite of a band-pass filter. The "notch" in the frequency response graph gives it its name.
This type of filter is highly selective, meaning it affects only a small band of frequencies. This makes it ideal for removing a single, unwanted interfering frequency from a signal, such as the 50Hz or 60Hz "hum" from AC power lines that can contaminate audio or sensor readings.
Center Frequency ($f_c$): This is the frequency at which the filter provides the maximum attenuation. It is the center of the "notch".
Q Factor (Quality Factor): The Q factor is a dimensionless parameter that describes how narrow the notch is. A higher Q factor corresponds to a narrower and deeper notch, making the filter more selective. A lower Q means a wider notch.
Bandwidth (BW): The range of frequencies that are attenuated. It's related to the center frequency and Q factor by the formula: $BW = f_c / Q$.
Passive Twin-T Notch Formula: For a standard Twin-T circuit, the center frequency is determined by the resistors (R) and capacitors (C):
$$f_c = \frac{1}{2 \cdot \pi \cdot R \cdot C}$$
- Audio Engineering: Removing power-line hum (50/60 Hz) from audio signals, eliminating feedback frequencies in live sound systems, and for creative sound shaping.
- Instrumentation & Control: Filtering out known interference frequencies in sensitive measurement equipment (like ECG/EEG machines).
- Radio Communications: Rejecting strong, interfering signals from nearby transmitters to improve reception of a desired signal.
- Speaker Crossovers: Used to flatten the impedance curve of a speaker driver at its resonant frequency, allowing for a more effective crossover design.
Notch Filter Calculator Setup Guide
A notch filter calculator becomes more useful when you define the interference source, target rejection frequency, and acceptable Q before selecting components. Engineers often compare a parallel notch filter calculator and an RLC notch filter calculator to decide whether the design needs a simple passive trap, a higher-Q network, or easier PCB tuning during validation.
Filter Tuning Checklist
- Set the reject frequency from the measured noise peak, not from a nominal guess.
- Check source impedance, load impedance, and component tolerance before fixing R, L, and C values.
- Re-measure bandwidth and insertion loss after layout, because parasitics shift the real notch depth.
FAQ
When is a parallel notch filter the better choice? A parallel notch filter is useful when the circuit needs a straightforward shunt path at one interference frequency and the surrounding impedance is well controlled.
Why compare an RLC notch filter calculator with test data? Real ESR, inductor resistance, and PCB parasitics move the center frequency, so calculator output should be checked against bench measurements.
Notch Filter Calculator Setup Guide
A notch filter calculator becomes more useful when you define the interference source, target rejection frequency, and acceptable Q before selecting components. Engineers often compare a parallel notch filter calculator and an RLC notch filter calculator to decide whether the design needs a simple passive trap, a higher-Q network, or easier PCB tuning during validation.
Filter Tuning Checklist
- Set the reject frequency from the measured noise peak, not from a nominal guess.
- Check source impedance, load impedance, and component tolerance before fixing R, L, and C values.
- Re-measure bandwidth and insertion loss after layout, because parasitics shift the real notch depth.
FAQ
When is a parallel notch filter the better choice? A parallel notch filter is useful when the circuit needs a straightforward shunt path at one interference frequency and the surrounding impedance is well controlled.
Why compare an RLC notch filter calculator with test data? Real ESR, inductor resistance, and PCB parasitics move the center frequency, so calculator output should be checked against bench measurements.
Notch Filter Calculator Setup Guide
A notch filter calculator becomes more useful when you define the interference source, target rejection frequency, and acceptable Q before selecting components. Engineers often compare a parallel notch filter calculator and an RLC notch filter calculator to decide whether the design needs a simple passive trap, a higher-Q network, or easier PCB tuning during validation.
Filter Tuning Checklist
- Set the reject frequency from the measured noise peak, not from a nominal guess.
- Check source impedance, load impedance, and component tolerance before fixing R, L, and C values.
- Re-measure bandwidth and insertion loss after layout, because parasitics shift the real notch depth.
FAQ
When is a parallel notch filter the better choice? A parallel notch filter is useful when the circuit needs a straightforward shunt path at one interference frequency and the surrounding impedance is well controlled.
Why compare an RLC notch filter calculator with test data? Real ESR, inductor resistance, and PCB parasitics move the center frequency, so calculator output should be checked against bench measurements.
Notch Filter Calculator Setup Guide
A notch filter calculator becomes more useful when you define the interference source, target rejection frequency, and acceptable Q before selecting components. Engineers often compare a parallel notch filter calculator and an RLC notch filter calculator to decide whether the design needs a simple passive trap, a higher-Q network, or easier PCB tuning during validation.
Filter Tuning Checklist
- Set the reject frequency from the measured noise peak, not from a nominal guess.
- Check source impedance, load impedance, and component tolerance before fixing R, L, and C values.
- Re-measure bandwidth and insertion loss after layout, because parasitics shift the real notch depth.
FAQ
When is a parallel notch filter the better choice? A parallel notch filter is useful when the circuit needs a straightforward shunt path at one interference frequency and the surrounding impedance is well controlled.
Why compare an RLC notch filter calculator with test data? Real ESR, inductor resistance, and PCB parasitics move the center frequency, so calculator output should be checked against bench measurements.
Notch Filter Calculator Setup Guide
A notch filter calculator becomes more useful when you define the interference source, target rejection frequency, and acceptable Q before selecting components. Engineers often compare a parallel notch filter calculator and an RLC notch filter calculator to decide whether the design needs a simple passive trap, a higher-Q network, or easier PCB tuning during validation.
Filter Tuning Checklist
- Set the reject frequency from the measured noise peak, not from a nominal guess.
- Check source impedance, load impedance, and component tolerance before fixing R, L, and C values.
- Re-measure bandwidth and insertion loss after layout, because parasitics shift the real notch depth.
FAQ
When is a parallel notch filter the better choice? A parallel notch filter is useful when the circuit needs a straightforward shunt path at one interference frequency and the surrounding impedance is well controlled.
Why compare an RLC notch filter calculator with test data? Real ESR, inductor resistance, and PCB parasitics move the center frequency, so calculator output should be checked against bench measurements.
Notch Filter Calculator Setup Guide
A notch filter calculator becomes more useful when you define the interference source, target rejection frequency, and acceptable Q before selecting components. Engineers often compare a parallel notch filter calculator and an RLC notch filter calculator to decide whether the design needs a simple passive trap, a higher-Q network, or easier PCB tuning during validation.
Filter Tuning Checklist
- Set the reject frequency from the measured noise peak, not from a nominal guess.
- Check source impedance, load impedance, and component tolerance before fixing R, L, and C values.
- Re-measure bandwidth and insertion loss after layout, because parasitics shift the real notch depth.
FAQ
When is a parallel notch filter the better choice? A parallel notch filter is useful when the circuit needs a straightforward shunt path at one interference frequency and the surrounding impedance is well controlled.
Why compare an RLC notch filter calculator with test data? Real ESR, inductor resistance, and PCB parasitics move the center frequency, so calculator output should be checked against bench measurements.
