Along with the Fairchild 670, the most hallowed of all studio equipment. Apparently, if you have an original one of these a holy presence descends upon your board. Scroll down for a look at how the attenuation/boost trick works. I divinely put it as a hint.
Attenuation + boost!
Here is an example of how that ‘trick’ works. In the chart below, the low frequency is set to 100; Low boost is set to 4, low attenuation is set to 9. Pretty cool. No wonder people have loved this for decades. By why not just use a “real” EQ and do it straight you may ask. Because this is great fun, and sounds SOOO smooth, and don’t be such a sourpuss.
Change the low frequency setting and the curve will move lower. For instance, at 30 the dip is around 200hZ. Changing the attenuation not only changes the amount of eq, it slightly slips the frequency around as well.