How to Calculate a Filter for Audio Frequencies

A low-pass audio filter will filter out all audio signals above a specific frequency, known as the cutoff frequency. Such a filter will help reduce high-pitched noise in your recordings. Designing the low-pass filter requires that you calculate the resistor and the capacitor for a specific cutoff frequency The calculation requires that you first determine the cutoff frequency, which is the highest frequency you will permit through your filter. Once you choose the cutoff frequency, you choose a capacitor value and then calculate the value of the resistor.

Things You'll Need

  • Resistor
  • Capacitor
  • Calculator
  • AC voltmeter
  • Ohmmeter
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Instructions

    • 1

      Select a frequency of 10,000 Hertz as your audio cutoff frequency. Choose a capacitor value that is readily available at the electronic store or in your electronic hobby kit. Choose 1 microFarad (0.000001 Farads) as the value for the capacitor.

    • 2

      Divide 0.159 by the product of the cutoff frequency (10,000) and the capacitor value (0.000001) to obtain 15.9 ohms.

    • 3

      Refine your calculation to take into account variations in actual resistor and capacitor values. Use a 10-ohm variable resistor and a 10-ohm fixed resistor for your actual circuit design. Adjust the 10-ohm variable resistor in your design such that audio frequencies above 10,000 Hertz will be attenuated. Measure the value of the variable resistor that gives optimum results and add it to the measured value of the 10-ohm resistor to determine the final resistance value.

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