MikeZ here, I'm the electrical engineer for the JamHub products. I've been lurking on the forum until now, but once I see dBu, dBV, impedance and input levels being thrown around I can't resist joining in
I wanted to clarify a few points and questions you brought up...But first off, thanks for doing such an in-depth review of the GreenRoom in your application. We have received a lot of positive comments from folks looking to use the JamHub products as a studio headphone mix router/amp.
tmarkov1 wrote:First, there are no technical specs included with the JamHub. With a pricetag of $499.99 MSRP there should be some disclosure as to the input sensitivity and impedances. No big whoop.
Audio specs are a funny thing. In my experience, even within a group of engineers, they cause confusion. There are no industry standards for the most part on how to measure them, and there are so many measurements out there it's difficult to take one piece of gear and accurately predict how it will behave with another piece of gear based on specs alone. It's really a bummer - things would be much easier for everyone if the specs were really meaningful.
Folks ask for specs usually wanting to answer an underlying question. In our experience - it's much more helpful to just address the underlying question. Instead of asking 'What's the input impedance?' I'd much rather have someone ask 'Can I plug my Taylor 414 with expression system directly in to the JamHub instrument input?", etc.
tmarkov1 wrote:Secondly: the inputs are -10dbu. What does that mean? If you are using a top shelf audio interface that has outputs rated at +4dbV, if you have output from your DAW coming out at just below 0db on your mix busses, the Sound coming in, once it goes through the JamHub's gain stage will be distorted, even though you will notice the LED is not red. I had to use my Focusrite Saffire DSP mixer for my interface and turn down the outputs to -10.
BTW - The 'industry standard' is actually -10dbV, and +4dBu (you have it backwards above
)Here's one example of where I think specs can be confusing. dBu and dbV. What the difference? (4dBu = 1.78dBV)
So until you really get into the world of audio gear engineering, you don't realize how misleading the innocent term 'dB' can be. For example: the term if db is very ambiguous in a DAW setting. The software says the mix bus is set to 0 dB (you see it on the meter). Is that dbV, dBU, or something else? Note how in the software it only says dB - they software designer does't know, and can't know, what the hardware will do. This means the meter on the DAW is not necessarily accurate to what is actually coming out of the physical output. So without actually measuring the voltage output of your DAW with an oscilloscope, you don't know what the output actually is. It could be much more than +4dBV. No matter what spec is, until you measure, you just don't know. If I had a nickel for every time I found an audio output spec that was way off from what it's spec sheet said.
But back to your problem - which I think you solved. I can set those bus/send levels in software on my M-Audio Delta 1010's - and I know for several interfaces this is possible. The JamHub, with the trim all the way turned down, should be able to accept an 'average' signal out from a DAW (maybe after being turned down a bit) without distortion. The JamHub is designed for instruments and processors to be plugged in to the inputs, so the recording gear that runs really 'hot' is sometimes too much. But all recording gear I have seen can either be turned down manually or switched down to a lover level.
(For additional reading on audio specs, check this article out: http://www.rane.com/note145.html. For converting all the audio units, myself and many engineers I know have this page bookmarked: http://www.sengpielaudio.com/calculator-db-volt.htm. And if you really want a deep dive, check out the 'Sound Reinforcement Handbook by David S. Jones / Yamaha)
tmarkov1 wrote:Now these results were strictly a limit test of the inputs. I ran a 1khz tone through at unity. Set my outputs to 0db, and then brought the gain on JamHub til the LED was just flashing red a bit. I then dropped a wav file of a song mixed with an average peak reading of -.03db. When I pressed play and brought the signal up on my solemix remote, the sound was completely distorted. Trimming back the input took none of the distortion away. So if you want to run your DAW stems to the jamhub, make sure you reduce the output levels of your audio interface to -10 BEFORE it gets to the JamHub.
Unfortunately, we encounter the same issue here. What's unity gain mean? It means something different in every device. If you set your outputs to 0dB, that actually doesn't say anything about the voltage level at the output. dB is just a ratio - and dB without the 'dbV' or 'dBu' reference doesn't mean anything realative to the outside world.
But, your underlying conclusion is absolutely correct - you need to turn the output gain down on the DAW hardware until there is no distortion. What exactly the level will be where there is not distortion is unclear.
....
But all the tech mumbo jumbo aside, Im excited you are happy with the product working for your particular situation. That's the important part. It's nice to eliminate a few miles of wiring from a studio environment
.Hope this is helpful, if you have any more q's, fire away.
-MikeZ