Using a second audio interface (DAC) in real time with the Quad Cortex?

Pardon me if this question as already been asked here!

One of the big downside of the quad cortex for me was not being not having any digital output in the form of SPDIF.

I already have my high end audio setup as so (PC → DAC → Headphone amp → Headphones).
With the FM3, I was able to connect the unit to my DAC via SPDIF and I could benefit my high end headphones through my whole setup without having to re-plug anything.

So, my question here is : is it possible to have two audio interface on my computer (One being the Quad Cortex, the second being my DAC).

The Quad acting as the input and my DAC as the output…

The caveat is I need to be able to jam/track/hear my playing through the quad cortex through the second interface (My DAC)

FYI : Yes, I could just plug my headphones in the Quad and swap when I need… but I’d like to have one nice “flow”, plus my headphones are particularly hard to drive, hence the need for the amp.

On Mac you can with this Rogue Amoeba | Loopback: Cable-Free Audio Routing but introduces a little bit of latency. I don’t think there’s a latency free solution to your problem but I’ll be happy to be proven wrong.

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This is what I feared…

So if I really want to use my high end headphones with headphone amp with the Quad Cortex in real time, it means I need to unplug the headphone amps from my external DAC to the Quad Cortex, so the Quad Cortex becomes the the DAC in this setup.

When I tried running the digital out from my Axe II through my prior DAC/headphone amp setup, Chord Hugo I, the latency on the playing part was so bad it was a deal killer (and I am not overly sensitive to latency). I am a bit surprised with the implication that you did not have latency issues running your FM3 digitally through your DAC.

What I found in my own experiences is the potential differences between the DAC from a modeler vs. dedicated audiophile systems while playing is not possible to notice when my mind is preoccupied with its concentration on playing. On the other hand, I did find that a good pairing of a headphone amp and headphones is a much more noticeable component of a rig as I was able to get noticeably more punch and depth, and was especially necessary until I switched to cans that were easier to drive.

Like you, I did not want to have to redo my cabling for different uses, so I switched to a Topping A90 amp that also doubles as a preamp with 2 sets of inputs and outputs. I also upgraded to the Axe III for its improved I/O and mixing of USB audio capabilities, among other things. So my setup before the QC arrived was XLR out from my Axe with a mixed signal of guitar tones and backing tracks going into the A90 headphone amp/preamp and output to either my headphones or use the A90 XLR out to my FRFR monitors. The real fun happens when I can get away with even more volume as I also run another set of outputs from the Axe to a stereo power amp and into a stereo pair of 2x12 cabs (actually 3 options to choose from, a 4x12 wired for stereo input and a separate 2x12 all with different speakers, and a De Lisle Amp Speaker selector to choose which cabs to select and also which amps to engage. I have not figured out yet if the QC has the routing abilities to send USB audio and guitar signal with cab IR to Out 1&2 while Out 3&4 excludes the USB audio and omits the cab modeling. Until I figure this out or until Neural eventually adds in this functionality, I’ll have to keep the Axe III in the signal chain.

If you want to avoid having to swap what your headphone amp is hooked up to for the at a reasonable cost while not stepping into loss of quality issues, you might want to look into preamps with the I/O optionality, price, and quality that fits your needs and wants. A mixer it a theoretical option as well but quality, size, and price will be tougher balance compared to a preamp.

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Again, if it’s a Mac you can easily aggregate (combine) several audio interfaces to one big interface which gets the same latency as the “worst” interface of the combined ones. For myself, I have combined a RME UCX firewire interface with the Quad Cortex USB interface and the latter turns up as 8 additional audio I/O channels in the Mac (for DAW and other uses). Roundtrip latency is 7ms (same as the Quad Cortex introduce).

On PC/Win I know that ASIO4ALL can combine audio cards but from what I’ve heard from users it introduces more latency and that it can’t compensate for clock discrepancy (which Core Audio does).

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I run my QC into my interface for monitoring purposes but record via USB

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I’m running the QC’s Main Out 1/2 into an Apollo 8 and monitoring that way. I have 2 monitors and a pair of headphones always plugged in and ready to go. The Apollo can drive my 80ohm headphones just fine, not sure about how hungrier phones might fare.

So to be clear it goes QC DAC-> Apollo ADC → Apollo DAC → my ears. I don’t hear any latency, same as if I was plugged directly in to the QC.

Not sure if this answers your question, but I thought I’d share my experience.

Thanks y’all for all the detail! I appreciate it!
I’m on Windows 10.

I haven’t noticed any delays while using my FM3 → Lynx Hilo (connected via SPDIF) → Amp, etc.

Although I’m switching my Hilo for a Sagra DAC in the upcoming days…
The Sagra also has SPDIF inputs, which means everything will work well with my FM3.

But the Quad Cortex still remains a mystery, here?

My needs are :

  • Listen to music WHILE I play, using my headphones setup
  • Not have to plug/replug my headphone amps and/or headphones from my audiophile setup

The FM3 lets me simply : sit down and enjoy, by plugin the FM3 to my DAC (via SPDIF as mentioned above)

Perhaps a Preamp could be the solution, here, I will look into it…
Also, my Lynx Hilo could fit the bill as it has Analog In (via XLR) and SPDIF out (for my Sagra DAC).
I would need to test out that the Sagra can both mix from USB and SPDIF, but this is overkill…

But my plans were to sell the Hilo, I cannot justify having all these expensive converters…

TL;DR
I’m ok with the Quad Cortex converter… My needs are not to use a separate converter, but really what I listed above, essentially using my headphone amp and headphone with the quad cortex while getting audio from my computer AND WITHOUT having to always plug/replug my setup from my computer.

You already mentioned it, but I think the preamp will be the best solution for you. You would use the QC’s DAC for USB audio when jamming with the guitar, and then switch over to your dedicated DAC for pure listening sessions. And you won’t have to change and cables, but you will have to buy another piece of gear. But you will also be layering in the ability to also have seamless switching between headphones and monitors or a hifi speaker setup without having to swap cable connections. I don’t have any dedicated preamp recommendations though other than being happy with my Topping A90 preamp/headphone amp combo, but I do know there are high quality options for good prices out there.

I wonder if this USB to SPDIF converter would work if plugged into the QC.
May be worth a try!

Amazon.com: LiNKFOR USB to SPDIF Coaxial RCA and 3.5mm Headphone Jack Converter USB DAC Optical Audio Adapter USB DAC PCM for Windows Mac PS4 PS3: Home Audio & Theater

Probably not as QC has an 8-channel class compliant USB interface while S/PDIF is just stereo.

That in itself shoudn’t be a problem. You can connect the QC to an iPad and it will stream stereo USB audio to the device.
I’ll find out soon enough - I ordered the device so will try it tomorrow.
There is also an 8 channel USB to Toslink device that does ADAT I/O. Not sure if that would work for free though.

USB Audio Streaming: USBStreamer B (minidsp.com)

Update on this. Sadly the USB to SPDIF convertor did not work with the QC.
QC USB doesn’t power the device so no cigar there. Too bad, I’ll keep the convertor since its a pretty handly way to get optical out from a mobile device.
I wonder if the device was powered via a hub it would work, haven’t investigated that…
Hope NueralDSP considers a USB add on to generate SPDIF out since it seems like this should be possible. I’d like to use it with my RME interface without tying up two analog inputs.

If you’re just using a DAW as opposed to routing audio between apps, an aggregate device would suffice. If using one device for input and another for output, you don’t even need to aggregate. The DAW should just let you select one as input and another as output. At least that’s how it works in Logic.

Been trying this for a few days, and getting really bad audio drift after a while with my Focusrite 18i20. Makes it unusable in the end without drift correction, which opens another can of worms

Which computer/OS-version? Are you running the QC or 18i20 as master clock at 48kHz? What happens when you use drift correction?

2014 Macbook pro, running OS 10.15. Tried using both QC and 18i20 as clock, everything set to 48khz. The resampling with drift correction eventually starts to cause buzzes and weird glitches

OK, does the QC work glitch free if you disconnect the 18i20 and select the QC as a single interface?

Fine at first, then after about half an hour huge lag