Do we need to add output low-pass filter to SigmaDSP chips?
The SigmaDSP DACs are sigma-delta and work at a higher frequency than the typical 48KHz sample rate, so you won't need a "brick wall" reconstruction filter afterward. For example, page 21 of the ADAU1701 data sheet shows that only a simple RC, or for better performance a one op-amp. filter will do:
The cap shown as C8 in the active filter should be 470pF, not 470uF as shown.
Thanks Bob. Yes, the out-of-band noise is much higher than the audio band, which is why we have a filter with a corner of 50 kHz, slightly above the sample rate.
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