Review of using a MOTU HDX-SDI (video capture device) as an audio interface in Sonar
So as a bit of background: I like to use home theater equipment for mixing and monitoring. In particular, because Audyssey MultEQ room correction is just amazing in my experience. While it is a nice thought to say "just have a good room" we all know that is hard to do, particularly in the home. Even when you do have a "good" room, it is amazing how many problems it can still have. Room correction really can help a lot and in my experience, Audyssey does a great job.
Thing is, if you want a hardware Audyssey processor, your only option is AV receivers or preamps. There is no standalone solution anymore (they did sell one at one point). The "studio" solution is IK's ARC product which works as a plugin. Really designed for two channels though, and of course only works if you have the plugin loaded whereas an outboard solution works on everything. Another issue with home theater gear is it only does processing like Audyssey on digital inputs. The multi-channel analogue in, when one is present, is just connected to the preamp, basically making the receiver in to a big volume control and power amp.
So for digital multi-channel audio your options are HDMI or nothing. For consumer grade stuff, no issue, any modern video card does audio via HDMI these days. For professional... well...
Enter the HDX-SDI and it's little brother the HD Express. Designed for video I/O on all kinds of formats, one of them being HDMI, and of course like all MOTU gear they do audio. They are both capable of acting as audio interfaces, including over HDMI and SDI, even with no video. When you put the HDX-SDI in playback mode and sync it to its internal clock, it'll generate blackburst sync (meaning a black video frame, with proper sync information) out of its outputs at whatever setting you specify. In that, you can embed audio from any source.
In terms of audio hardware, the HDX-SDI is pretty impressive. Both HDMI and SDI have 8 channels of embedded audio, there are 8 balanced analogue I/Os that MOTU says have 112dB SNR, and there is 8 channels of AES/EBU I/O on DB25 breakouts. So pretty much, 8 channels of most anything except ADAT and TDIF. It supports 96kHz on all inputs and outputs except for SDI, which is limited to 48kHz as per the SDI spec.
The audio capabilities with that hardware aren't as impressive, but are adequate. The unit processes 16 inputs and outputs divided in to two banks of 8. You can assign the output banks as you wish to analogue, AES, HDMI, and SDI. You can mirror one to all of them, have only one of them turned on, whatever. For input you have to choose which input routes to which bank. As such you can only use two of the input types at once. There is no mixing or routing or any of that. Just simple mapping. You can adjust trim on analogue inputs but that's it.
In terms of software interfacing it has WDM/WASAPI drivers and ASIO drivers. In both cases, it enumerates itself as a bunch of stereo pairs, both to Windows and to any ASIO host. This means you can't use it for surround playback in arbitrary programs like a DVD player or videogames. You need to have something like Sonar that handles its own routing and mapping. Sonar is happy with it in both modes. However something to note is that it doesn't appear to be able to change ASIO buffer size. It is set at 512 samples, and reports a total latency of 1226 samples for output. If you launch the ASIO panel, it just brings up the MOTU video panel, which has no ASIO settings. In WASAPI mode, you can adjust latency in Sonar itself, I don't know if the card is actually listening to said adjustments or not.
Using the HDX-SDI in Sonar, well, it works just like you'd expect. Sonar happily plays audio, and it gets routed out the HDMI interface, in to the receiver, and in to my speakers. No issues I've seen so far. The inputs and outputs show up and are assigned as you would with any soundcard. I can't see any issues.
All in all I'd give it maybe a B-. It works for what I want, and I appear to be the only person in the world who's ever wanted to do this. However the capabilities are a little basic. I would much rather have the capabilities of a pro soundcard, including MOTU's products, available, just with an HDMI out. It is clearly video focused and audio is something of an afterthought, despite the large amount of I/Os. That said, it does what is being asked of it and it is one of the only solutions on the market that can.