Adjustable analog filter

[m98]

Hi,

I need a notch filter for audio signals at line level. It should have an adjustable center frequency of 800-8000 Hz with 1 Hz steps.
Thought that I could build the filter with discrete components and adjust it with digital potentiometers, but that seems to get big, costly and difficult to calibrate.
Could a switched capacitor filter ic be an alternative? I've found this application note, featuring the MAX7410. But it only has a Q of 1.7, which is too low. I need something about 10.
Any suggestions?

Thanks for your help

m98

[T3sl4co1l]

If you need it so precisely, you should probably just do it with a DSP.  Switched capacitor might be okay (if you don't mind that it's Maxim), but mind the other aspects of them as well (reduced high frequency bandwidth, switching noise).

If you don't need exact steps, but rather a tolerance range is acceptable, then a number of methods might be applicable.  See also OTA filter circuits.

Tim

[Circlotron]

Do you need to do the filtering in real time? If not, maybe record it then play back and notch it with Audacity or something similar.

[m98]

Yes, filtering needs to be real-time. Didn't want to use a DSP, as I don't have any experience with them. Also that would be a bit overkill.
After reading some application notes and datasheets of switched capacitor ics, I found that the "newer" generations have only a negligible clock feedthrough and switching noise. I think that the LTC1067 fits my application.