HP AF filter ISO

Discussion in 'General Electronics Chat' started by Karl, Apr 20, 2009.

  1. Karl

    Thread Starter New Member

    Apr 20, 2009
    I was wondering if anyone knows of a simple, slick H.P audio filter circuit? I’ve messed around with twin Tees however looking for a cutoff frequency around 100 Hz. It’s for my (audio) repeater and wish to cut off anything below that point. Comm Spec makes a tone decoder with a built-in circuit however the cutoff is 300 Hz.

    Now, having said that, this active circuit would have to have an extremely high “Q” because of the percentages involved. Perhaps something out of the “Stereo” cross over thinking process?

    Karl in Spokane
  2. beenthere

    Retired Moderator

    Apr 20, 2004
  3. Darren Holdstock

    Active Member

    Feb 10, 2009
    High-Q filters can sound nasty in audio applications due to the vicious phase shifts near the rolloff frequency and the ringing transient response. A good old Sallen and Key with a Bessel response (ζ=0.8659) will give a nice sound; cascade* two or more filters for a steeper rolloff.

    * Use filter tables for the RC values for each individual stage, don't cascade several identical filters.