Re: Question about SNR
The SNR=6.02Nb+1.76 formula appears when you consider the quantization noise introduced by an IDEAL DAC (or ADC for that matter).
Therefore, in this calculation it is considered the output signal of the DAC directly (no LPF). Note also that an ideal DAC does not have generate distortion. The output spectrum of this ideal DAC is composed by the sinewave and the quatization noise.
In reality you have more noise (thermal, ...) and also distortion.
Rgds