Dual Phones Outputs; 5-Band Parametric Eq - RME Audio ADI-2 Pro User Manual

8.2 Dual Phones Outputs

Many features and design decisions on the ADI-2 Pro come from personal usage and experi-
ence. 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 un-
plug 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 interfaces 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 vol-
ume 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 Pro has two stereo DA-converters to similarly provide two independent and individual
phones outputs. Adding a third DAC for the line outputs would raise cost, space and effort tre-
mendously, 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 main (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 out-
put 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)
Comparing headphones with the Fireface UFX and 802 comes with another, big advantage:
TotalMix 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 frequen-
cies so the phones become more similar. This makes it much easier to hear the basic, but finer
differences in the phones sound signature.
Having worked extensively with this luxurious double output solution, there is no question why
the ADI-2 Pro got two fully independent, identical 'Extreme Power' headphone outputs, and
individual equalizers for both outputs. This is indeed the premium way to compare headphones
seriously 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 disadvan-
tages - 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 ex-
act 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 2 or below, the 5 band parametric EQ turns into a very efficient tool
even for problematic phones.
User's Guide ADI-2 Pro © RME
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