This is a really cool device that I would never have known about had I not worked in a studio where it was needed. I've discovered that simply converting from an unbalanced -10db audio source to a +4db balanced source in Pro Tools will increase lots of noise and excess level, which is something that is not acceptable at a professional studio. This box will take signals of both types and convert them to the other noiselessly and superbly. There aren't any other special features, this is a simple device with one primary function. It has an extra component that you attack to it in order to let it fit onto a rack, and can also be wall-mounted.
This is a really simple box to use. Just run the unbalanced audio signal through the unbalanced input and then use the XLR outputs for the output. You'll turn a previously unbalanced signal into a balanced one. It's great to use with other recording devices or audio sources such as computer sound cards, DAT converters, and other such things. It's also good for taking balanced audio sources and making them -10db unbalanced, though I haven't needed to do that really and am not sure why it would be totally necessary other than for pure loudness' sake.
This is probably one of the more transparent pieces of gear you'll find out there. The whole point of it is to take unbalanced audio and make it balanced, which is a problematic venture if you aren't sure what you're doing. This box makes it simple and easy, and doesn't sacrifice audio quality in the least. This is why it's such a good purchase for the studio owner, it will allow audio that is basically unusable to sound great with no manipulation or processing required.
While this is certainly not the most necessary piece of gear for the home studio owner to have, it is great if you are doing unconventional methods of recording, or which to use audio from an unconventional source and have it be of a useable level and quality. Basically, if you find yourself needing to balance unbalanced audio, this is your guy right here. It's certainly no joke to just drop 200 dollars on a piece of gear, so make sure you'll use it a couple times at least. If you make some money off of a recording that needs this gear it more or less pays for itself. So I'd have to recommend this pretty highly overall.
The Henry Engineering Matchbox HD is what they call a stereo level and impedance interface. Basically, it converts unbalanced -10 db levels to a balanced +4 connection. It has connections in the form of XLRs for two inputs and two outputs, as well as RCA connections for the same. The Matchbox HD has a built in power supply that has a standard power cable attached to it. It isn't in rack mountable form as it is a small box to sit on your desk or on top of your rack. In other words, it isn't something that needs to be set up all the time.
Setting up the Henry Engineering Matchbox HD is a very simple process. It has basic connections, so once they are in place you're all good to go. There aren't any parameters, as it simply does the job at hand without needing to be told what to do. There isn't really anything that you need to know about the Matchbox HD beyond making the proper connections, so a manual isn't something that is needed unless perhaps you're having some sort of technical difficulty or something like that.
The sound quality of the Henry Engineering Matchbox HD is absolutely superb. It is definitely the cleanest sounding impedance converter that I've used, although it isn't something that it necessary if you already have the proper set up. However, if in fact you do need a very high quality impedance converter and leveler, you can't get a much better sounding one than the Matchbox HD.
Although probably only necessary in professional recording studios who need to have the proper converters and high quality connections available at all times, for what it does the Henry Engineering Matchbox HD can't be beat. It converts your impedance cleanly without adding any noise, hum, and any other sound of it's own whatsoever. In fact, it eliminates all noise that you will get with other lesser impedance converting devices. If you're working in a professional studio environment and need something like this, I'd definitely encourage you to go with the Matchbox HD.