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Voltage controlled filter

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Does anyone know how to make a voltage controlled filter?  I am making a guitar effect called the auto-wah which in theory uses an envelope follower to supply the voltage to a VCF [(Voltage Controlled Filter) bandpass/lowpass/highpass filter].  The filter will change it's cutoff frequency or Q due to the change in voltage from the envelope follower which in turn gets it's voltage from the guitar signal.  Every guitar note will give a different sound, seeing as the envelope of every note is different.  The only piece I need to finish this thing is how to control the filter with a voltage.  Any ideas?  Thanks in advance!

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Yes. There are several ways to do this. Voltage control has to be built in as part of the circuit. It is rarely an add-on. In the most basic type of this design, you can use the bandpass section of a state variable filter and use a voltage variable resistance instead of a pot. Can you post the circuit that you are currently using? Voltage Controlled filters can be made in a very wide variety of types. The auto-wah is also known as an envelope filter.


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