Src (Sample Rate Conversion); Crossfeed - RME Audio ADI-2 Pro SE User Manual

Here is an example on how it works: the user's typical lowest level listening volume is at -35 dB
at the unit. This value is now set by the user as Low Vol Ref in the Loudness menu. Then Bass
and Treble Gain can be set between 0 and +10 dB. Default is +7 dB for both. Increasing the
volume by turning the Volume knob causes the gain in Bass and Treble to be lowered smoothly
over a range of 20 dB. So when Volume is set to -15 dB, the music is not only quite loud, but
Loudness' Bass and Treble are then at 0 dB gain. See chapter 34.15 for graphs.
No matter how sensitive the connected phones or speakers are, no matter how much increase in
Bass and Treble are desired – with the ADI-2/4 Pro SE one can finally adjust it to meet the per-
sonal hearing and taste. Loudness finally works as it should have worked from the start - another
unique feature in the ADI-2/4 Pro SE.

8.6 SRC (Sample Rate Conversion)

The ADI-2/4 Pro SE includes an asynchronous stereo sample rate converter (SRC). A SRC allows
a conversion of the sample rate in real-time. The converter used in the ADI-2/4 Pro SE operates
practically without loss of signal quality, so no audible artefacts or noise is added. It also handles
intersample peaks (ISP) up to +3 dBFS without added distortion. In fact, the SRC works so well
that we could recommend to just leave it on at all times, thus eliminating all clock problems right
from the start. Which is the case for the SPDIF input in Auto mode.
The SRC offers a maximum conversion rate of 1:7 or 7:1, respectively. Thus, 192 kHz can be
converted to any sample rate down to 44.1 kHz, and 32 kHz can be converted to any frequency
up to 192 kHz. Higher sample rates than 192 kHz are not supported.
An SRC not only converts sample rates, it also serves as a clock decoupler. With SRC active,
even non-synchronizable devices (CD-players, DAT machines, etc.) can be used in a setup of
digital devices, just as if they were externally synchronized. The SRC decouples input and output
clock and sets the output clock to the common reference, thus allowing the combination of differ-
ent clock-sources. For example having the ADI-2/4 Pro SE synchronized to an AES signal, a CD
player connected to SPDIF input can only be used when the SRC is set to SPDIF. It then decou-
ples the clock of the non-synchronizable CD player, preventing clock problems and drop outs. As
the incoming clock phase is no longer fixed when the SRC is activated, the SPDIF Sync state in
the State Overview screen will always show lock.
When using the internal clock, every SRC also works as a jitter killer. However, the ADI-2/4 Pro
SE is equipped with SteadyClock FS, thus operating as perfect jitter killer with any clock source.
However again, a jittery input signal might degrade the quality of the sample rate conversion. The
ADI-2/4 Pro SE therefore has a second SteadyClock exclusively for the current SRC input signal
to make the sample rate conversion process as reliable and transparent as possible.
A SRC can also be used to upsample audio. A 44.1 kHz source can be converted to 192 kHz in
real-time and thus played back with the DAC set to 192 kHz. The usefulness of this process is
questionable. There is zero content added, so the exact same audio is played back. The only
change is that the DAC's oversampling filters are moved far out of the audible range. But even at
44.1 kHz the ADI-2/4 Pro SE's filters are inaudibly high, and the process of sample rate conver-
sion also uses those lower filters during its first conversion process.

8.7 Crossfeed

While headphones open the sound stage and make everything easier to hear and to locate by
spreading the narrow sound field of stereo speakers to the left/right extreme, some people would
like to have a listening situation that is more comparable to a standard speaker setup. The ADI-
2/4 Pro SE includes Crossfeed to address this wish. Crossfeed reduces the artificial surround
ambience that some productions have to make them sound better on speakers, but which sounds
unnatural on a headphone. It uses the Bauer Binaural method, with five selectable strengths of
narrowing the upper frequencies. This advanced method, which also includes a small delay and
correction of the frequency response, works quite well, and is another useful addition as well as
a unique feature on a device like the ADI-2/4 Pro SE.
User's Guide ADI-2/4 Pro SE – v 1.0
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