Does anyone have a circuit for a low pass audio filter with variable cut-off frequency? An added nice feature would be a way of varying the damping ratio of the filter - i.e. being able to select any extra boost at the cut-off.
Similarly an audio high pass filter with variable cut-off and or damping.
Thanks
Chris snipped-for-privacy@pobox.com
Chris, this filter allows independent fg and Q control, the output is chosen not to have a Q dependent gain. The ganged pot for the frequency has resistors in series according to the desired range and minimum input impedance.
|| +--------||--------+ | ||C | IN Rv_ | Rv_ |\ | o-+-|___|-+-|___|-+-----|+\ | | A | A |C | >-+ | |...|...| --- +-|-/ | +---+ +---+ --- | |/ | | | .-. | +---->| |10k === | | | GND | '-' | | OP2134 | .-. /| | | |5k6 OUT /+|--+ | | o---+-< | '-' | \-|-+ | | \| | === +------+ GND (created by AACircuit v1.28 beta 10/06/04
Hi Chris,
Check out switched-capacitor filters (MF or LMF series). These are really nice when a variable cut-off is required while mostly preserving the filter characteristics. The cut-off is simply moved around by changing the clock frequency. A great part to start experimenting with is the LMF100 from National Semiconductor. Linear Technology also has a variety of such filter chips.
I had used this filter type in a Doppler receiver design and switched-capacitor was the only economical way to go for that application.
Regards, Joerg
Many thanks to everyone who replied. There are some great ideas there that I'll take on board.
Chris
Look here: "Filter Design in Thirty Seconds"
Hope that helps
cut-off
ratio
"Dr Chris Andrews"
** A pot and a cap in series will do that.** " any " ????
Care to define your terms and goal ???
** We talking active ?Passive ??
Variable slope ??
Speaker x-over ??
.................. Phil
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