What ADC and DAC to pair with CamillaDSP for subwoofer room correction?

[Statman2022]

I'm currently using a MiniDSP2x4HD for room correction on my four subwoofers, but I was looking to try out CamillaDSP on my computer since it can support more filters than the MiniDSP2x4HD. Currently, I have a single RCA connection going from my AVR to miniDSP2x4HD and then four RCA connections going from there to each of the subwoofers.

Apparently, I can use the MiniDSP2x4HD as either an ADC or DAC with its USB connection going to the computer running CamillaDSP. If I'm using it as an ADC, I will need to buy a new DAC that will take USB from the computer and output to four RCA plugs to go to my subwoofers. On the other hand, if I use the MiniDSP as a DAC, I'll need to buy an ADC that takes in my AVR's RCA subwoofer out and outputs the digitized signal to USB for my computer running CamillaDSP.

Which option to people recommend for my use-case? Buy a new ADC or new DAC? And what are things I need to consider like syncing and sample rates? I guess I could just buy a second MiniDSP, but I was wondering if there are cheaper options out there.

 

[AnalogSteph]

How old is your 2x4HD? Looks like a new version has been out for 2+ years, with what I'd consider much better converters than the original.

Before you go out and buy anything, do you happen to have an onboard line-in that you might be able to put to good use? I mean, we're talking subwoofers here, so if for simplicity's sake we're assuming a 100ish Hz bandwidth that would mean a 23 dB uplift in SNR (probably not as much in practice due to 1/f noise levels, but still), plus we're not exactly sensitive to noise down there. So a relatively modest dynamic range (say, around 90 dB) is fine, and nobody cares about digital filter performance much. Use 48 kHz, a lot of older chips have degraded performance at 44.1.

Note that your average Realtek tends to have input gain set to +6 dB by default, so you'll have to change that if you want it to accept the full 1 Vrms and change.

I would also strongly suggest making (or cobbling together) a cable that permits you to use a stereo line-in as a virtual balanced input, so you can later subtract L-R in the DSP. (Note: Best determine input channel imbalance and compensate for it as well. You also see a 1-sample delay between channels sometimes which should be taken care of then.) Think RaneNote 110 #18 if both sides are grounded somewhere. If one side is floating and the multimeter indicates substantial common-mode AC voltage between them (typically from power supply mains filter leakage), definitely connect RCA shell to shield as well in order to avoid damaging the input.
If you know AVR sub output impedance (from specs or service docs) you can try matching that on the RCA to black connection for better impedance balance and hence CMRR; it can be quite substantial. You may find an RCA to 1/4" TRS cable easier to make, then you can use an off-the-shelf 1/4" to 3.5 mm adapter. Modifying an off-the-shelf 3.5 mm stereo cable to begin with would be another option.

If you have a multichannel onboard output you can also use that, but your subs may not be floating or have pseudo-balanced inputs so there is some potential for ground loops like that.

You WILL have to accommodate for asynchronous sample rates in CamillaDSP either way.