Teensy 3.2 - I2s object - CS4334 DAC - Aliasing

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hallmar

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Hey!

Ok so I've made an 8 voice poly synth with four choosable waveforms, 2 operator FM and a selectable 8 voice karplus strong synth.
I've implemented Cirrus Logic's CS4334 16-bit DAC and everything works fine for sine and triangle waveforms.
But there's a problem for square and sawtooth waveforms, I can clearly hear aliasing artifacts that get worse the higher the frequency(normal for aliasing) and it's annoying the hell out of me. I can hear the aliasing at around 200hz and up with the square wave.

How do I deal with this?
Is there anything in the I2s object that could be improved or is it in the Waveform modulated object?

I've included my circuit schematic, CS4334 datasheet and a node diagram of my audio system.

View attachment CS4334-5-8-9_F7-1142050.pdf
View attachment node.ino
View attachment schem.pdf
 
Your schematic shows C4 at 4.7 uF.

But the equation on page 4 in the CS4334 datasheet seems to say that capacitor ought to be in the 4 to 6 nF range. Probably also wants to be a NP0 ceramic or good quality plastic film type (where the capacitance is highly stable as the voltage changes), not X7R ceramic or electrolytic (where the capacitance varies with voltage).
 
Oh yeah, i forgot to update the schematic, messed up the calculations when i designed it at first :)
Right now i have a 100nF capacitor for C4, because it's all i had laying around.

The capacitor alongside R14+input impedance of the op amp(R7 or 1k ohm) should form a low pass.
(I got a capacitance of 5nF for an RL of 1k ohm).
 
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