RME Audio ADI-2 Pro, User Manual

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User’s Guide ADI-2/4 Pro SE - v 1.0
34.9 ADI-2/4 Pro SE 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 soundcard. That
limits signal to noise ratio, frequency response and distortion values to the ones of said sound-
card.
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 25 years.
One of the ADI-2/4 Pro SE development goals was to make it so good that it can serve as hard-
ware frontend for audio measurement software. Accepting a few limitations the hardware should
be capable to measure most of the audio interfaces, DACs, ADCs and analog equipment that is
in daily use by many. To achieve this the ADI-2/4 Pro SE must have superior tech specs.
The superior real-world specs listed and shown throughout this manual make the ADI-2/4 Pro SE
one of the best hardware frontends available. 120 dB dynamic range (RMS unweighted), zero
hum, support for different reference levels, super low-noise inputs and outputs, very low THD
values, galvanically isolated operation through battery power, very small level tolerances, versa-
tile handling and configuration
– the ADI shines on both desk as well as in the measurement lab!
Tips for optimal measurement results
Improve the signal-to-noise ratio (and thus THD+N) at the analog input by mono operation
To do this, place the source on both inputs simultaneously using a split cable, and activate M/S
processing in the analog input. The left channel now has an SNR of 124 dB (AES17) instead of
121 dB at unchanged level.
Improve signal-to-noise ratio (and thus THD+N) at the analog output by mono operation
To do this, use a split cable to connect both outputs, which must output the same signal, to one
cable. This 'short circuit' uses internal resistors of the ADI to improve the SNR by 2.5 dB.
THD /THD+N Measurement
Measurements of THD
and THD+N often don’t require an active notch filter in front of the analog
input. However, using one improves the measurement accuracy of high-quality DUTs, so it can
be quite useful.
Maximum resolution at the analog input
Whenever possible, the analog input should be set to the lowest Ref Level. While the SNR hardly
changes from +24 dBu to +1 dBu (120 to 119 dB), the noise level changes with the Ref Level.
This means: with +24 dBu set the noise floor is at -96 dBu, at +1 dBu it is at -118 dBu. So for low-
level signals, changing the Ref Level can make 23 dB lower signals be detected.
Measuring Frequency Response
As most current devices support sample rates up to 192 kHz, a hardware frontend must be capa-
ble of 384 kHz, or it cannot fully measure the frequency response of a 192 kHz device.
Single Sample Impuls
Playback of a real single sample impulse can be achieved with the filter selection NOS, without
any pre- and post ringing.