That classic 70's EQ, now in API 500 format for your studio!
OPERATING THE EQUALISER
Begin with all boost/cut controls - those with centre detents, set to their mid way ('0') positions. Adjust the low and high mid frequency sweep controls to their minimum positions (fully anticlockwise). The 50Hz high pass 'Filter' switch should be in the out position. Set the frequency select switches controlling the high and low shelving sections, to 120Hz and 12kHz respectively. Lastly, set the 'EQ' switch to the 'in' position (the associated LED will illuminate).
Rotation of the high frequency shelving control in a clockwise direction emphasises high frequencies, while turning the control in an anti-clockwise direction from centre attenuates high frequencies.
Operating the 'frequency select' switch in the high frequency section introduces a subtle change of emphasis to the affected high frequencies, as the shelving 'knee' is changed from 12kHz to 8kHz. Likewise, rotating the low frequency shelving control in a clockwise direction will emphasise low frequencies, while turning the control in an anti-clockwise direction from centre attenuates low frequencies. Adjusting the 'frequency select' switch in the low section introduces
a subtle change of emphasis on the affected low frequencies by altering the shelving point from 120Hz down to 60Hz.
The 'low mid' and 'high mid' equaliser sections are peaking filters. Adjustment of their parameters is achieved by use of the boost/cut knob and its associated frequency sweep knob. Boost or cut of a given frequency is performed by moving that control from its centre detent position: clockwise for boost, anti-clockwise to cut. The frequency to be boosted or cut is selected by the frequency sweep control knob. The range of frequencies of the 'low mid' control extends from 100Hz up to 1.5kHz.
For the 'high mid' sweep, the frequency range begins at 1kHz (overlapping with the low mid section) and continues up to 15kHz.
The Series 80B 500 Series EQ incorporates a classic four band equaliser which is identicalto that employed in the Trident Series 80 console. It consists of frequency switchable high and low pass shelving sections, coupled with two swept low and high mid range bands and a switchable 50Hz, 12dB per octave filter. Both swept midranges have been carefully chosen for maximum effect on music programme and a good degree of overlap is provided.
Finally, selecting the 'Filter' switch introduces a smooth, 50Hz, 12dB/octave roll-off to effectively eliminate 'rumble' caused by, among other things, someone's feet moving about near a microphone stand, nearby traffic noise and AC systems. The amount of boost (accentuation) or cut (attenuation) that is applied to the audio signal is entirely dependent on the programme content and it is not our intention to advise on this. Application of equalisation is a very subjective matter and is best learned by experiment. The equaliser bypass switch 'EQ' is a useful facility for comparing the signal before and after the application of equalization.