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 Pro. 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 calculation 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. Balanced Phones mode control 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. The number of available EQ channels is reduced to 2 (1 x stereo). EQ can still be used with Analog Input, Main Output 1/2 or Phones Out 3/4, but only one of these.
• At sample rates 705.6 kHz and up Crossfeed or EQ (1 x stereo) can be active, not both at the same time.
The high sample rates available in the ADI-2 Pro also exceed the capabilities of the digital I/Os. Both AES and SPDIF are limited to 192 kHz, and there is no way around it (except a special, one channel SMUX mode, see chapter 14.1.2, Setup Clock). Therefore all higher sample rates are only usable analog and in USB mode. And in iOS mode when using an iPad/iPhone with an app that supports such high sample rates (Neutron, Onkyo HF-Player etc.).
