The dual-channel ART Digital Pro VLA II mic preamp has an on-board A-D converter that caters for both RCA and optical forms of S/PDIF, as well as the AES3 format.
I have a Roland Quad Capture [audio interface], which I’m very happy with. I would like to use the digital inputs in addition to the two analogue inputs, but there’s nothing I know of on the market that will allow me to do this. Can you offer any ideas or suggestions — other than buying another interface?
SOS Forum post
SOS Technical Editor Hugh Robjohns replies: The digital inputs on the Roland interface come in the form of a coaxial S/PDIF input, so if you want to route analogue sources into the interface via that port you will need an analogue-to-digital (A-D) converter, and if it’s specifically extra mic channels you want then, if you want a single product to do it all, what you really want is a dual-channel mic preamp with built-in A-D converter and a coaxial S/PDIF output. You could then connect the two using a standard RCA phono cable that’s intended to convey digital audio or video signals. (Note that standard RCA phono cables, intended to connect analogue hi-fi gear, tend to be too ‘lossy’ and can be unreliable in this particular role).
There are a number of dual-channel mic preamps on the market which offer digital outputs, and these range from the remarkably good ART Digital Pro VLA II at around $299, up to the stunning Grace Design m201 with digital card at an eye-watering $3499.
The only potential ‘gotcha’ to watch out for is in the digital clocking. In any digital audio system, there can only be one master clock — everything else must slave to that. In your situation, that will mean setting the converter in the external mic preamp to run on its internal clock as the system master, and configure the Roland interface to use the S/PDIF digital input as its clock source, so it works as a clock slave.
SOS Reviews Editor Matt Houghton adds: One thing you didn’t mention was your budget — so it’s worth adding that if you only need to add line-level inputs on a budget (or mic-level but you already own some preamps), it’s worth checking whether you already own another product with an A-D conversion stage built in.
For example, in the past, I’ve pressed my TC Electronic M300 external effects processor into service as a line-level A-D converter. Just plug your line-level source into the effects box’s analogue inputs, and connect the effects box’s S/PDIF output to your audio interface. Obviously, it has to be an effects unit for which the effects themselves can be bypassed! They won’t be the very best converters or clock in the world, but assuming it’s not a decades-old device, they should sound more than clean enough to get you up and running.
Published August 2018
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