А сам ЦАП работает с дискретизированным сигналом, любой ЦАП, не только сигма-дельта. Поэтому все составляющие, которые попадают в нечетные зоны Найквиста, будут прямо перенесены в 1-ю зону, а из четных - зеркально (с инверсией фазы).
"A DAC's quantization noise and distortion determine its SNR. ... Real DACs also have nonlinearities due to process mismatches and imperfect bit-weight scaling. Nonideal switching characteristics also add distortion and nonlinearity. The most prominent DAC spurs are usually due to nonideal switching characteristics, which, along with any nonlinearity in the transfer function, appear as lower order harmonics of the fundamental. Both quantization noise and the nonideal DAC properties produce a response that consists of harmonically related spurs of the fundamental. This relationship is the key to understanding how to predict the frequency location of the prominent spurs. --! Harmonics alias because the DAC is a time-sampled system. !-- As a result, the carrier's harmonics, the reference clock, and the reference clock's harmonics create numerous sum- and difference-mixing products. The well-defined mathematical relationship of these products makes predicting the spur locations possible. Harmonics beyond the first Nyquist zone are mapped back to the first Nyquist zone (Figure 11)."