User's Manual

User’s Guide ADI-2 Pro FS – v 2.5

An effective fix can be provided by a digital compensation filter, put into the DA path of the ADI-

2 Pro, always and only active at 384 kHz sample rate. This filter is fine-tuned to achieve a near

perfect frequency response when self-measuring from DA to AD (loop) at 384 kHz.

The picture below shows the ADI-2 Pro in loopback mode, XLR Out to In, at 384 kHz sample

rate. The red curve is the DAC's original frequency response, starting at 10 kHz (everything

below is straighter than a line), showing its early decline with -0.5 dB already at 70 kHz. The

black line shows the available frequency response at 192 kHz sample rate with Sharp filters

selected. It gives an idea which area a frontend should be able to measure accurately (and that

frequency response is already the most extended one can find, as RME modified the DAC's

analog output filters for improved linearity).

The blue curve shows the effect of RME's digital compensation filter at 384 kHz sample rate.

The frequency response is now ruler flat up to 90 kHz, with no noticeable decrease in the area

of the 192 kHz sample. With this filter the ADI-2 Pro can perfectly measure any 192 kHz (and

lower, of course) operated device with highest accuracy at fractions of a dB!

Naturally the added digital filter compensation will cause distortion whenever a signal is applied

whose level exceeds the gain of the filter at the respective frequency. For example at 100 kHz,

the maximum undistorted digital level is no longer 0 dBFS, but -2 dBFS. Astonishingly this tech-

nical limitation has only a small negative impact in real-world operation, for several reasons.

For all users:

• The correction is only applied to the DAC at 384 kHz. The ADC's frequency response

reaches far higher, no correction is necessary or applied to it.

• The additional filter only affects 384 kHz PCM operation. In DSD mode (here DSD128) the

filter is automatically deactivated.

• The additional filter has no meaning for normal music reproduction/playback of 384 kHz

PCM material, as that one does not include such high frequencies at nearly full scale level.