Which of the following is NOT a source that can be assigned to the Grand Master Fader?

The Grand Master Fader is a control element typically used in audio mixing to adjust the overall volume of all channels in a mix. In many audio mixing systems, certain sources can be assigned to the Grand Master Fader to ensure they are included in the overall volume control.

The reason option D is correct is that "ST C and D" suggests a specific combination of sources that may not be eligible for assignment to the Grand Master Fader. When certain sources such as stereo channels (like ST C and D) are not designed to be controlled collectively through the Grand Master Fader, they stand apart from other sources that can.

In contrast, other options, such as the individual sources ST A, GM AUX, and AUX 11 and 12, are typically designed for inclusion in the Grand Master Fader's control structure. This makes them valid choices for assignment, as they contribute to the overall balance of the audio mix.

Thus, the correct choice highlights a specific grouping of sources that do not align with the intended functionality of the Grand Master Fader, emphasizing the importance of understanding which audio sources are compatible with this overall control mechanism.