AP2700 Digital options, the second life.

Today I want to tell you about how to make useful the DIO part of an old but well old AP SYS2722/2522, which has only SPDIF I/O and quite useless nowadays. I have to use my AP with my USB DACs and SPDIF/TOSLINK I/O no use, hence, I losing convenient features of the AP2700 software(don't tell me that external sweep is ok too!). To make my AP "great again" I made a simple USB "SPDIF" optical bridge with 24/192 IN/OUT at CM6631A and default FW. See the attached schematic. Now I can make a fast and precise frequency response or THD+N vs frequency etc. After the external sweep, which drives me crazy, now I feel much better.


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E.g. all Envy24HT-based with SPDIF input (ESI Juli, Audiotrak Prodigy 192, Infrasonic Quartet,M-Audio Audiophile192,...), PCI-e ESI Juli Xt, CMI8788-based cards with SPDIF input (PCI Xonar D2, PCI-e Xonar D2X), any USB card with CM6331A and SPDIF input, like your device. Some motherboards have SPDIF-in header to their Intel HDA codec, e.g. Gigabyte GA-Z87X-OC, easy to google out.
CM6631A is a USB-audio device controller with SPDIF in/out. IMO any soundcard with SPDIF inputs/outputs could be used.

I do have some familiarity with CM6631(A) and I know it's used in quite a few USB audio interfaces. Hence being surprised by what seemed to be a USB-host type of usage as I had imagined this was a stand-alone direct SPDIF to USB conversion... I now get it that what IVX described involves the use of a computer and re-routing of audio streams. Still neat although indeed there are quite many audio interfaces offering this already (granted, for a higher cost).

@IVX - any limitations due to re-routing, have you noticed any performance degradation compared to SPDIF? Any timing or synch issues restricting some measurements? I have a SYS-2722 on its way and being able to use it directly with USB-only DACs is something that I am highly interested in. As a dScope owner I am looking forward for the few extra dB of SINAD (not that many actually, approx. 5dB on the input side, probably a bit more for the generator) but upfront I am not sure whether the AP will end up replacing my trusted dScope. dScope is very versatile, has extremely capable software and among many others allows direct use of sound interfaces for both input and output (ASAPI or WDM) - and this since many years ago, way before AP implemented this with their current series on analyzers.
axismundi, how do you can use 2722 digital generator with USB DAC test if 2722 has SPDIF digital outputs only? I didn't find the way to use it and made that USB/SPDIF 24/192 interface device for that.
Absolutely, there is no way unless you improvise. Which is what you did.

On paper one could imagine a SPDIF to USB-host converter, removing the need of routing through a PC. One could connect the USB DAC to this host rather than through a computer. I guess doable but compatibility will be the key limitation, USB audio is not quite the best of the standards around.

You did not mention whether you encounter any limitations, would you mind commenting on that? Thanks
axismundi, how do you can use 2722 digital generator with USB DAC test if 2722 has SPDIF digital outputs only? I didn't find the way to use it and made that USB/SPDIF 24/192 interface device for that.

So to make sure I understand it correctly: you take S/PDIF output from the 2722, convert that to USB, send that USB signal to the DAC and analyze the DAC output with the 2722?

OK, thanks. Then I have some more questions if I may.

IIRC the 2722 can insert specific values of jitter or missing bits etc in the S/PDIF stream, and can then measure how the DAC handles that.
When you use an S/PDIF converter, I guess you lose that test possibility.

And assuming a perfect jitterless S/PDIF, what is the 'quality' of whatever comes out of the USB side of the adapter?



2011-02-10 6:40 pm
I still do not uderstand the routing. AP -> SPDIF -> USB device -> USB host = computer -> DAC -> analog -> AP? Then why not directly AP -> SPDIF -> DAC with SPDIF input?
Not all DACs have SPDIF input. I for one use the ASIO/USB testing functionality in my dScope mostly when testing portable players. Quite a few of them can be used as USB DACs when connected to a computer but do not have SPDIF input.
right, many DACs have USB only and AP2700 simply can't test such stuff comfortably. APx5** SW may test USB DACs but if you buy special option for >$3000 and if your DAC supports ASIO only! That's why Amir's tests often limited at 16 bits. I sent him free my SPDIF/USB interface to solve that issue but he still didn't reply me about it. The same situation with WolfX700 tester from china(Page Redirection one more tester), I sent him my board free too, and he didn't reply.