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tegleg
Joined: Feb 07, 2014 Posts: 3 Location: 0,0,0
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Posted: Fri Feb 07, 2014 5:30 pm Post subject:
help demistify vcf's please Subject description: having trouble getting my head round a few things |
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hello
sorry for the vague title.
i can make a basic hi or lo pass filter with a resistor and a capacitor, the resistor of course controls the cutoff.
i can make for example a 'decay' circuit that smoothly drops from +9v to 0 that is triggered from a sequencer.
how would i (in as few analog parts as possible) make that voltage controll the filter cutoff?
i can't get my head round how to replace a resistor with a voltage in a circuit like that. i can add some pictures is somethings not clear.
thanks for any help |
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JovianPyx
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
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Posted: Fri Feb 07, 2014 5:48 pm Post subject:
Re: help demistify vcf's please Subject description: having trouble getting my head round a few things |
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tegleg wrote: | hello
sorry for the vague title.
i can make a basic hi or lo pass filter with a resistor and a capacitor, the resistor of course controls the cutoff. |
Both the resistor and the capacitor control cutoff.
tegleg wrote: | i can make for example a 'decay' circuit that smoothly drops from +9v to 0 that is triggered from a sequencer.
how would i (in as few analog parts as possible) make that voltage controll the filter cutoff?
i can't get my head round how to replace a resistor with a voltage in a circuit like that. i can add some pictures is somethings not clear.
thanks for any help |
First, the filter you described above is the simplest and least interesting of all filters. It is a single pole filter. If you want the kind of sounds you hear from modular synthesizer filters, then you want a filter with more poles - at least 2. There are many types. It depends on what you're after as to which filter is best. An easy to build filter that has the control aspects you described (voltage control over cutoff) would be the state variable filter. This can be done with an LM13700 IC - there are many many schematics for this filter type on the web. Just google "analog state variable filter" as a starting point. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
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tegleg
Joined: Feb 07, 2014 Posts: 3 Location: 0,0,0
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Posted: Sat Feb 08, 2014 1:51 pm Post subject:
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thats exactly what i needed thank you
its sometimes difficult to find something if you dont know what its called.
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