The presence of this ultrasonic noise with SACD can also be seen in fig.5, which shows wideband spectral analyses of both SACD and external 24-bit sources with a dithered 1kHz tone that is actually below the Omega's noise floor. (I usually use "digital black" for this test, but the Omega appears to shut off its analog output when it detects this signal.) The LPCM data results in a "white" noise floor that starts to rise above 50kHz, presumably due to the sigma-delta DAC's own noise-shaping. However, the DSD data result in a noise floor that peaks at -42dB around 120kHz, before rolling off at higher frequencies due to the SACD license's mandated low-pass filter.

Fig.5 Classé Omega, 1/3-octave spectrum of 10Hz at -120dBFS, with noise and spuriae (from top to bottom above 10kHz): DSD SACD data, 24-bit LPCM data (right channel dashed).

As implied earlier by the fig.4 spectral analyses, the Omega's linearity error was very low down to -100dBFS, though with a little more noise than normal (fig.6). This graph was taken from the balanced outputs using CD data; spot-checking the linearity using SACD data gave the same result. The waveform of an undithered 1kHz tone at -90.31dBFS was essentially perfect (fig.7).

Fig.6 Classé Omega, balanced left-channel departure from linearity, 16-bit CD data (2dB/vertical div.).

Fig.7 Classé Omega, waveform of undithered 1kHz sinewave at -90.31dBFS, 16-bit CD data.

Distortion was a little higher than I expected, and, unusually, worse from the balanced outputs than from the unbalanced. Fig.8, for example, shows an FFT-derived spectrum of the unbalanced output while the player decoded CD data representing a full-scale 50Hz tone. The second (100Hz), third (150Hz), fourth (200Hz), and fifth (250Hz) harmonics can all be seen. Though the third harmonic is the highest in level, this is still negligible at -74dB (0.02%).

Fig.8 Classé Omega, unbalanced spectrum of 50Hz sinewave, DC-1kHz, at 0dBFS into 100k ohms (linear frequency scale).