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Originally Posted by PaRaNoId  I did it! Yeah me! 
I bought two polypropelyne .15 microfarad caps and soldered them b/w pins 2 and 3 with the ground going straight trough. On my DAW, i ran pink noise out and back in through my patch bay. Then using a freq analyzer (Voxengo SPAN) i measured the result- a very flat line. Then i patched into the cicuit i made (very crude TRS to TRS thing) and tested it again. My analyzer showed a very steady dip starting at about 250 hz and sounded relatively uncolored. So now, im guessing if i want to force the corner freq down, i should install a shunt resistor of a value of 20k or greater? Or is that because i should have used .16 micro farad caps? This is really fun! |
Glad you're learning and even gladder you're having a good time doing it.
Adding a shunt resistor (to the downstream side of the capacitors) will RAISE the corner frequency, not lower it. The C and the R are both in the denominator of our equation
f = 1/2πRC
which means that making R or C higher will make f lower, and vice versa. Your shunt resistor will be in parallel with the actual load impedance, and serve to lower the effective load impedance seen by the capacitors.
By the way, the reason this equation works is because you're finding the frequency at which the impedance of the capacitor is equal to the resistance of the load. Resistors, in theory, have the same impedance at every frequency. It's not dynamic or "reactive". Capacitors, in theory, have an impedance that continuously declines as frequency increases. This is called Capacitive Reactance because the impedance changes (reacts) based on the frequency in question. The 3rd component in this train of thought is an inductor, whose impedance (again, in theory) continuously increases with frequency, just the opposite of a capacitor. Its impedance is called Inductive Reactance.
So, if you have a series impedance and a shunt impedance, you get a voltage divider. If one or both of the impedances is reactive, it will be a voltage divider whose attenuation is frequency-dependent. In the case of your hi-pass filter, the series element decreases with frequency while the shunt is fixed. If you swapped them (series resistor with a shunt capacitor), you'd get a low-pass filter instead. Or, if you replaced the series capacitor with an inductor, you would also get a low-pass filter. These building blocks let you build many different kinds of filters.