Thanks for the math lesson @atomicbob. Makes sense now why my amplitudes are lower than yours with my Realtek codec. I'll make one last feeble attempt to plea my case. The four sine waves hidden in the noise of my -90dB trace, and the lack of clear "spikes" at each zero crossing of my -70dB trace aren't evidence of v2? Or I guess I'm just seeing what I hope to see. SPDIF Input - 1kHz @ -70dBFS (v1) I promise, this is the last time I'll ask about my firmware. I'm gonna follow @Skyline's sage advice.