I performed a full set of measurements on the Moon 891 using my Audio Precision SYS2722 system,1 repeating some of the testing with the magazine’s higher-performance APx555 analyzer. For logistic reasons, I measured a different sample from that reviewed by JVS; mine had the serial number 310A22426340. Before I lifted the Moon onto the test bench, I unfastened the three transit bolts on its base—a good thing I read the startup guide before starting the testing! I installed Moon’s MiND app on my iPad mini, which allows the 891’s volume to be controlled but doesn’t allow settings to be adjusted.
As JVS only auditioned the Moon 891’s digital inputs in his review—I understand that another reviewer will be reporting on the sound of the 891 as an analog preamplifier in a follow-up—I looked first at the performance of the Moon’s DAC. I used the AES3 and coaxial and optical S/PDIF inputs, all of which accepted data sampled at rates up to 192kHz, as well as USB data sourced from my MacBook Pro. Apple’s USB Prober utility identified the Moon as “USB HD Audio” from “MOON,” with the serial number string “2 (None),” and indicated that the USB port operated in the optimal isochronous asynchronous mode. The AudioMIDI utility
