RME Audio ADI-2 Pro, User Manual

Page: 17 / 114

User’s Guide ADI-2/4 Pro SE – v 1.0
17
8.8 DSP Limitations
There is never enough DSP power
– no matter how much you add (frustrated developer).
That is true even for the ADI-2/4 Pro SE. Although being equipped with a quite capable 2.17 Giga
FLOPS
DSP chip, plus using the FPGA to perform further calculations (RME’s virtual DSP for
mixing/routing, level meters, filtering, Crossfeed), 768 kHz sample rate takes its toll. The calcula-
tion power available at 48 kHz is divided by 16 (!) then. Even at 384 kHz it is just 1/8 of that at 48
kHz. The DSP in the ADI- 2 Pro performs:
Bass/Treble and Loudness for 6 channels
5-band parametric EQ for 6 channels
Standard phase functions for 6 channels
Crossfeed for 4 channels
30-Band bi-quad bandpass filter spectral analyzer
Peak Level meters for all channels
Display rendering
Volume control on 4 channels
Several controller-like functions, like volume ramp-up, mute, signal routing control etc.
Configuration of the ASP (Audio Signal Proce3ssor) inside the ADC
DSD to PCM conversion (for level meters)
At 48 kHz that is no big deal, at 192 kHz it already needs efficient coding and a better DSP chip.
But at 768 kHz you need a DSP with 4 times the power of the ‘better’ one. Therefore there is no
way around disabling some functions at higher sample rates. Fortunately those limitations have
only small impact in real-world usage:

At sample rates 352.8 kHz and up the Bass, Treble and Loudness function is deactivated.

At sample rates 705.6 kHz and 768 kHz the number of available EQ channels is reduced to
2 (1 x stereo). EQ can still be used with Analog Input, Line Out 1/2 or Phones Out 3/4, but
only one of these.
The high sample rates available in the ADI-2/4 Pro SE also exceed the capabilities of the digital
I/Os. Both AES and SPDIF are limited to 192 kHz. Therefore all higher sample rates are only
usable analog and in USB mode, but also in iOS mode when using an iPad/iPhone with an app
that supports such high sample rates (Neutron, Onkyo HF-Player etc.).
DSD can not be processed digitally. Therefore DSP functions like Bass, Treble, Loudness, EQ
etc. are disabled in DSD mode. The volume control is no longer done by the DSP, but the DAC
chip. You won’t notice that, volume operation at the ADI-2/4 Pro SE is seamless and behaves
identical in any mode. In DSD mode the DSP performs an additional DSD to PCM conversion, to
be able to show the audio signal on the level meters and for the Analyzer
– another unique feature
of the ADI-2 series.