I have a Cirrus Logic CS4334 audio DAC chip working (datasheet here). One thing that confuses me is the "typical connection diagram" circuitry from the datasheet shown below.
In my experience with audio DACs, the R and C values on the output lines are for a typical resistor/capacitor (RC) low pass filter where part of the calculation is the cutoff frequency (F sub S). However, I'm used to the circuit and calculation used for the RC filter being different than what is used in the circuit diagram below.
I'm used to an RC low pass filter circuit being like this where the signal being filtered first goes through a resistor and then there is a capacitor to ground following the resistor. However, in the circuit below the signal first has the capacitor to ground then the resistor to ground (???). Maybe this is a different kind of low pass filter I'm not aware of?
Also, note the equation for the C value in the diagram below. Say I was a low pass filter with frequency cutoff of 20KHz and I'm going to use a 22 ohm resistor. I take it I should use a capacitor around 188 nanofarads as shown in my math below, agree?
C = (22 + 560) / (4π * 20000 * 22 * 560) = 1.879e-7 = 188nF
Any insights anyone might have to help me understand this better would be much appreciated. Thank you.