Ver. 2.0 - ©Phædrus Audio Ltd. 2015 All rights reserved.
Architecture of the PHILTER equaliser
Controls
Bass, Treble and Frequency-select controls
The equalisation controls on the PHILTER are simple and intuitive to operate. Remember, these circuits were
invented well before the complex, analogue equalisers of the nineteen-seventies. When the middle frequency-
control is turned to the two most anti-clockwise positions, the bass and treble controls (marked with the
appropriate music clefs) act as they do on a hi-fi; as a boost and cut control: clockwise to boost (in 2dB steps);
anti-clockwise to cut (in 2dB steps). The central control may be used to modify the character of the treble-
frequency boost. Depending on the frequency setting: 2.5kHz; 3.5kHz; 5kHz; 8kHz; 10kHz; 12kHz, when the treble
control is rotated clockwise beyond the central position, boost is applied with a broad peak in the response at the
indicated frequency. Note that this control is NOT active when treble-frequency cut is applied; this always
remains as a shelving response. The graph below illustrates the 121 separate response curves which result form
the 121 combinations of treble and bass control when the central switch selects the 5kHz, peaking-response.
Note that the cut curves do not exhibit a complementary notch to the boost peak.
