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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! wink

Download of the firmware update files (original update thread):

https://www.forum.rme-audio.de/viewtopic.php?id=27280

Regards
Matthias Carstens
RME

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Re: ADI-2 Pro Firmware Update DSP 87 (details)

Here are some pictures to illustrate the changes. All AD filters, SD Sharp/Sharp and SD Slow/Slow have been optimized, individually in all sample rates from 44.1 up to 192 kHz. These measurements are loopback setups, therefore include the error of the ADI-2 Pro's DAC chip. We verified with other references that we did not optimize for DA-errors. We only compensated the ADC part, which still makes the loopback application much better than before.

Please also note the extreme zoom to show the ripple. Usually you would use at least 5 dB as vertical resolution (instead of the 1 dB used here), or even more to see the behavior at lowest and highest frequency. In such cases there is no ripple visible anymore.

 
https://www.rme-audio.de/images/adi2pro_sharp_441.png

https://www.rme-audio.de/images/adi2pro_sharp_96.png

https://www.rme-audio.de/images/adi2pro_sharp_192.png

https://www.rme-audio.de/images/adi2pro_slow_441.png

https://www.rme-audio.de/images/adi2pro_slow_96.png

https://www.rme-audio.de/images/adi2pro_slow_192.png

Regards
Matthias Carstens
RME

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Re: ADI-2 Pro Firmware Update DSP 87 (details)

This measurement demonstrates the achieved improvement although at 44.1 Sharp it is not the highest one. I scaled the diagram area to be identical to one you can find online, where the reviewer used an Audio Precision Audio Analyzer  to measure the ADI-2 Pro's frequency response. Pixel area, vertical and horizontal settings are all identical. Finding the ripple (red line) the reviewer commented:

I was a bit disappointed to see the ringing (up and down swings) which I assume it is due to the anti-aliasing filter. While the variations are small, it starts ringing at around 1 kHz! Will have to analyze this further in the future.


https://www.rme-audio.de/images/adi2pro_asr_comparison.png


Now with the new firmware (blue line) I am sure the remaining ringing would not have provoked any comment.

Please note that in said review measurement the AP has been set to measure the frequency response in a very coarse way. It can do much better, though. HpW shows all details correctly, there are 7 dips, not 5 as seen in the review measurement.

Regards
Matthias Carstens
RME