Topic: ADI-2 Pro Firmware Update DSP 87 (details)
To ripple or not...
Firmware DSP 87 brings an interesting new feature - well, interesting for geeks and nerds (like us). It addresses the ripple seen from the AD converter chip with frequency response measurements at higher resolution, at sample rates 44.1 up to 192 kHz. While this is nowhere near audible, the ADI-2 Pro is also used as measurement front-end. With today's high quality devices and measurements using a very high resolution, that ripple becomes visible, and is both distracting as well as a problem for documentation.
Other ADC chips typically have only a fourth of that ripple, which is why it mostly stays invisible. Firmware version DSP21 now adds a unique, phase-linear compensation filter, that reduces the ripple significantly. Not completely, but enough that in normal measurements the ripple is no longer visually obvious. The filter has zero effect on the audio performance. No phase shift, no change in SNR, THD or bandwidth, not in impulse response and not in latency. It just reduces the ripple by up to 86% (depends on mode and sample rate). That's why it is not an option but always on, and only switched off automatically with DSD recording.
The compensation filter also works on the already quite linear 176/192 kHz sample rates, improving linearity to a fabulous level. Note that 352.8 kHz and up do not have any (!) ripple, which is one of the reasons the manual recommends 384 kHz for audio measurements.
So you can shrug your shoulders and continue using the ADI-2 Pro as it is, or add a small pristine improvement on top of the jewel that the ADI-2 Pro already is. Your choice!
Download of the firmware update files (original update thread):