@Cuthbert 80: true, what you said. the truth is in the listening, but like many have said before:
measure twice, cut once!
anyway, there is some info on iFi's site for their older and more costly iFi Pro iDSD device's MQA decoder. rather convoluted and difficult to understand by me, a mere amateur hobbyist, but maybe some of the good folks here with more knowledge might be able to decipher this information:
"
GTO TRICKLE-DOWN
Unlike the xCore-200 series which include built-in DSP capabilities, implementing MQA on xCore-100 required the ground-up design of a DSP engine. With the DSP engine now available, our natural inclination was to have our new filter baked onto the XMOS Firmware.
Technical assistance came from an unexpected source; MQA. Using very different filter parameters as part of a more complex system including the decoder section requires serious DSP chops. The implementation of MQA rendering on the original xCore-100 series XMOS processors widely used in the iFi products required extensive DSP work.
This took some extra work, and some fine-tuning of resource allocation, however with the version 5.3C of our XMOS firmware we now offer this new, Global Transient Optimised digital filter to all our customers, including just about all our legacy products, as an alternate option to the filters implemented in the DAC chip that apply for version 5.30 and before.
TECHNICAL BACKDROP
The ‘Gibbs Transient Optimised’ filter was developed by iFi according to our specifications in conjunction with the MQA team. We must make clear that GTO is not directly related to filter types used by MQA, it is not “MQA through the backdoor”, but instead what we feel is the optimum solution for the playback of digital audio that has not undergone the MQA process. We would like to thank MQA for their technical assistance in integrating this into our firmware."
This is copied and pasted from iFi's document here:
https://ifi-audio.com/wp-content/uploads/2019/04/iFi-audio-Tech-Note-The-GTO-Filter.pdf