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8.2 Dual Phones Outputs
Many features and design decisions on the ADI-2/4 Pro SE come from personal usage and ex-
perience. For example when comparing headphones: it turns out to be very difficult when having
just one headphone output. Changing the phones on the head is already a disrupting process
which hinders easy comparison, but without proper level adjustment first, and the need to unplug
one and to plug the other, comparisons are only possible for coarse differences. At RME we are
used to compare headphones connected to a Fireface UFX or 802. These exceptional audio in-
terfaces have two independent phones outputs. The included TotalMix FX, a DSP based mixing
engine, allows to route the same audio signal to both outputs, with individual volume settings, and
no need to unplug / plug anything. So if one phone is too low in volume it is simple to raise it, or
lower the other one, to get them on the same volume, making a comparison much easier.
The ADI-2/4 Pro SE has two stereo DA-converters to similarly provide two independent and indi-
vidual phones outputs. Adding a third DAC for the line outputs would raise cost, space and effort
tremendously, while listening on two phones at the same time or comparing phones this way is a
seldom task. Therefore one phones output, labelled PH 1/2 on the front, shares the Line (rear)
output signal. Although this phones output reaches the same technical specs as PH 3/4, and also
has the exact same Extreme Power output stage, it is considered the 'spare' Phones output for
comparing phones, dual phones usage, and balanced phones operation – or just use it as another
unbalanced line output. The main Phones output, which is independent from the rear outputs, is
PH 3/4. For most users it will be the only output ever needed and used. And because it is the
most often used one it was intentionally moved away from the Volume knob to ease operation,
resulting in an unusual arrangement with PH 3/4 left and PH 1/2 right.
As explained a major reason to have not only two, but two independent phones outputs is that it
offers a much better way to compare headphones. But there is more to it, see next chapter.
8.3 5-band Parametric EQ (PEQ), 7-band with Bass/Treble
Comparing headphones with the Fireface UFX and 802 comes with another, big advantage: To-
talMix FX controls a 3-band parametric equalizer (PEQ), again independent for both outputs. So
if one phone has too much or too little bass, it's easy to reduce or increase lower frequencies so
the phones become more similar. This makes it much easier to hear the basic, but finer differ-
ences in the phones sound signature.
Having worked extensively with this luxurious double output solution, there is no question why the
ADI-2/4 Pro SE got two fully independent, identical Extreme Power headphone outputs, and indi-
vidual equalizers for both outputs. This is indeed the premium way to compare headphones seri-
ously as well as efficiently.
While no equalization as well as listening only straight linear has been a mantra for many years,
research has proven that no ears are identical, and that especially in near-field listening (with
phones) the biological differences alone make individual equalization mandatory. No two pairs of
ears hear the same thing, that's a fact. Additionally personal taste makes people like different
sound signatures, which can easily be copied or made more similar (equalized...) on different
headphones using a good EQ. The advantages of using an EQ outweigh any alleged disad-
vantages - which so often turn out to be wrong at closer inspection.
Having used PEQ to linearize as well as to better meet personal taste with a variety of head-
phones, RME found 5 bands of parametric EQ to be the best balance between occupied DSP
resources and efficient sound treatment. While it is true that on some phones rebuilding an exact
response curve needs more than 5 bands, one quickly realizes that very narrow peaks and
notches make no audible difference when compensating them. Their acoustical energy is too low
to get audible. Ignoring those narrow peaks/notches and only taking care of deviations that require
a quality factor of 3 or below, the 5 band parametric EQ turns into a very efficient tool even for
problematic phones.
User's Guide ADI-2/4 Pro SE – v 1.0
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