Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Controls
Bass, Treble and Frequency-select controls
The equali sati on controls on the PHILTER ar e si mple and i ntui ti ve to operate. Remem ber, these
ci rcui ts w ere i nvented w ell befor e the complex, analogue equali sers of the ni neteen-sev enti es.
When the mi ddle fr equency-control i s turned to the tw o most anti -clockwi se posi ti ons, the bass
and treble controls (marked w i th the appropri ate musi c clefs) act as they do on a hi -fi ; as a boos t
and cut control: clockw i se to boos t (i n 2dB s teps); ani t-clockwi se to cut (i n 2dB steps). The central
control may be used to modi fy the character of the treble-frequency boost. Dependi ng on the
frequency setti ng: 2.5kHz; 3.5kH z; 5kH z; 8kH z; 10kH z; 12kH z, w hen the trebl e control i s rotated
clockwi se beyond the central posi ti on, boos t i s appli ed wi th a broad peak i n the response at the
i ndi cated frequency. Note that thi s control i s NOT acti ve w hen treble-fr equency cut i s appli ed;
thi s alw ays remai ns as a shelvi ng response. The graph below i llustrates the 121 separate response
curves w hi ch result form the 121 com bi nati ons of treble and bass control w hen the central swi tch
selects the 5kH z, peaki ng-respons e. Note that the cut curves do not ex hi bi t a complementary
notch to the boos t peak.