Topic: Firmware Update ADI-2 DAC 66 / 41 - Loopback
Since about one month the ADI-2 DAC ships with an ES9028Q2M as DAC chip. This is our first unit with ESS. In the transition process we had to learn a lot, about the chip itself, how it behaves, how to best use it, what influence the clocking has, what tech specs are missing in the 'secret' data sheet (tons of..), and how to make the DAC operate and behave as similar as possible to the former AKM chip.
The result was the shipping version FPGA 60 and DSP 39. This is a big step up from the former 35 / 35, the numbers indeed equal many steps of development. And we aren’t finished, some fine-tuning is always possible and will be done.
Such fine-tuning is the main reason for the new version FPGA 66 DSP 41. We managed to get the THD+N performance identical between asynchronous and quasi-synchronous mode, so the new option Varipitch has been removed. That mode (DAC fully synchronous to the incoming SteadyClock) is now always active. Its big advantage (and the reason to add it in the first place) was that in this mode the chip does not perform a random, short mute state after sample rate change with audio already playing. So we can now offer the performance of the ESS chip with the better behavior of the AKM chip.
But this update is also useful for older DACs, as it officially adds the new option Loopback to USB. It is described in text and block diagram of the updated manual 2.8:
This feature is mostly useful for Mac users. Under Windows anyone can use DIGICheck to visualize and analyze the current playback data, as our special ASIO support allows to read back that playback data. Under Mac OS this is not possible, and without analog input and digital output the obvious workaround (loopback) is not possible.
Now it is. All ADI-2 DACs have a record path for the digital SPDIF input. The new option simply puts the current playback data there, so instead of the digital input data DigiCheck will see the playback data. You even have the option to send back the pre FX data (pure playback) or post FX data (including EQ etc. and volume control). Finally DigiCheck can be fully used with the ADI-2 DAC on the Mac.
Edit: Another change was missing in the readme (added just now). CC mode: at sample rate mismatch USB record data will be muted, the USB sample rate shown red in the Status Overview screen. To explain: if you feed SPDIF at 44.1 kHz and connect an iPhone via USB (Class Compliant mode), then want to record this SPDIF signal with an app that only supports and works at 48 kHz, the 48 in the USB column will be shown in red color and the USB record data will be muted. Otherwise - as the unit does not include sample rate conversion - the recording is quite distorted.