CCIF and DIM30 measurements added to Engine-400 specification sheet
Measuring amplifier THD at 1kHz and 6,67kHz does not reveal all non linearities. Depending on how the structure has been designed there could be other artefacts that can only be revealed with more advanced test signals. CCIF is a twin tone measurement where the difference is measured, usually between 18kHz and 19kHz i.e. at 1kHz. This reveals how good the linearity is at high frequencies. Since Engine-400 has the same loop gain in the entire audio band this measurement looks similar to the THD-measurement i.e. nothing new is revealed.
DIM30 is a way of trying to reveal if there are internal saturations in cascaded gain stages when exposed to high slew rate signals. It is tested by generating a large slew limited 3,15kHz square wave and then adding a smaller 15kHz sine wave on top (pretty much like music can be when a drum is hit at the same time as a trumpet is playing).
Engine-400 shows good behaviour with this challenging signal and it actually again reminds you about the THD vs power graph.