User Manual

User’s Guide ADI-2 Pro - v 1.91

One should not underestimate the effect on higher sample rates with PCM and DSD, though.

Those require to transfer data of multiples of the amount typical for a channel at 48 kHz:

Base 48 kHz 96 kHz 192 kHz/DSD64 384 kHz/DSD128 768 kHz/DSD256

Channels 2 4 8 16 32

Now it should be clear why the above advice can be quite important even for an ADI-2 Pro. In

Multi-channel mode the numbers are even higher:

Base 48 kHz 96 kHz 192 kHz/DSD64 384 kHz/DSD128 768 kHz/DSD256

Channels 8 16 32 64 128

Although on the edge, 384 kHz would work. But 768 kHz - no way. As the ADI-2 Pro should

work under iOS as well, which has a system limit in transfer bandwidth, its USB transfer mode

is limited to 192 kHz in Multi-channel mode. Fortunately that is no real limitation. The additional

digital I/Os activated then do not support higher sample rates than 192 kHz anyway.

But once again it must be noted: at 192 kHz the USB interface is challenged with data amounts

equalling 32 audio channels transfer, although only 8 are in use.

34.18 ADI-2 Pro as Hardware I/O for Measurements

Audio measurement systems have been (and still are) quite expensive. Several years ago

much cheaper software based solutions started to replace the expensive references, whenever

the measurements did not require absolute accuracy. Although the software itself might be

100% accurate, the hardware used as generator and analyzer is often just a consumer sound-

card. That limits signal to noise ratio, frequency response and distortion values to the ones of

said soundcard.

At RME not only the well-known references Audio Precision and Rohde&Schwarz are used, but

also simpler, sometimes even more flexible or unusual solutions. A long-time favourite is HpW

Works, a software analyzer and generator program that has been in use by RME developers for

more than 20 years. Most measurement diagrams shown in this manual were done with it

(thank you Hans-Peter Widmer to provide us with this superb tool over all those years!). In

many cases we only use the expensive systems for verification. Not because HpW would

measure wrong, but because of the limited hardware that serves as I/O.

That leads us straight to the ADI-2 Pro. One of its development goals was to make it so good

that it can serve as hardware frontend for audio measurement software. Accepting a few limita-

tions the hardware should be capable to easily measure most of the audio interfaces, DACs,

ADCs and analog equipment that is in daily use by many. In fact the ADI-2 Pro was designed to

outperform any previous RME device.

The superior real-world specs listed and shown throughout this manual make the ADI-2 Pro one

of the best hardware frontends available. 120 dB dynamic range (RMS unweighted), zero hum,

support for different reference levels, super low-noise outputs, very low THD values, galvani-

cally isolated operation through battery power, special 384 kHz SPDIF mode via optical connec-

tion, and level tolerances that are just mind blowingly small - this little box will rock your desk!

As most current devices support sample rates up to 192 kHz, a hardware frontend must be

capable of 384 kHz, or it cannot fully measure the frequency response of a 192 kHz device. But

even then the result might not be what one expects. In fact at 384 kHz the DAC used in the ADI-

2 Pro uses a fixed slow filter which causes an early drop at higher frequencies than when meas-

uring at 192 kHz sample rate with Sharp filter selected. Being keen to measure deviations in the

range of ± 0.1 dB with stellar accuracy it doesn't help that at a drop of -1.5 dB the 384 kHz filter

slowly starts to outperform the 192 kHz one.