Front Panel Controls Input; Front Panel Controls 8.1 Input; Limiter - RME Audio ADI-8 QS User Manual

8. Front Panel Controls
8.1 Input
In the INPUT area, the select key causes a change of the analog input
sensitivity, referenced to digital full scale level (0 dBFS) of the AD-
converters. The choices are: +4.2 dBu (-10 dBV compatible), +13 dBu,
+19 dBu and +24 dBu. As the adaptation is performed in the analog do-
main, the ADI-8 QS achieves the highest possible values for Signal to
Noise ratio and distortion in any setting.
After selecting DIG, the digital input signal is routed to the digital outputs, with the AD-
conversion being deactivated. The level meters now show the level of the digital input signal.

8.2 Limiter

The LIMITER is available as analog function (MODE ANA), digital function (MODE DIG), or
combined (both LEDs lit).
Analog Limiter
For the ADI-8 QS, RME developed a new fully symmetrical circuit design with
digitally controlled release time. While the analog limiter is constantly within
the signal path, it operates fully transparent as long as there is no control sig-
nal generated, so does not cause noise or distortion. This special feature
made it possible to define a threshold of +3 dB in deactivated mode, prevent-
ing an overload of more than 3 dB of the AD-converters. This avoids not only
extreme overload effects, but also prevents the AD-converters from being
damaged.
Both the fully symmetrical design and the digitally controlled release time contribute to the re-
duction of the unavoidable distortion of a peak limiter (linearity errors of the control elements,
generation of the control voltage). The distortion value of about 0.3% stays the same at any
level and any frequency.
Another exceptional feature is the ability to handle extremely high levels. At the level references
+24 dBu, +19 dBu and +13 dBu up to +30 dBu can be fed, the signal is still limited correctly (-3
dBFS), THD is still 0.3%. At the setting +4.2 dBu the maximum unclipped input level is +24 dBu.
So there is more than 20 dB overload possible!
Note: As with all such basic designs, increasing dynamic ratio and gain reduction causes audi-
ble pumping effects.
Digital Limiter
The digital limiter is a non linear compressor. The input signal is processed with a special ampli-
tude function. The resulting third order harmonics are widely masked by the original signal.
The digital limiter allows for additional headroom of up to 5 dB without audible clipping (clipping:
brickwall limiting leading to high distortion). It also allows for an increase of the loudness without
increasing the maximum peak level, similar to the effect known as Maximizer. Unlike the analog
limiter there is no attack and release time and therefore no pumping effects.
The strength of the limiter effect can be adjusted in the Setup menu in steps of 1.5, 3, 4 and 5
dB, indicating the maximum level or loudness gain (chapter 9.14).
User's Guide ADI-8 QS © RME
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