SM Pro Audio's M-Patch ($179) is a passive volume control that works as a patch-control device for routing audio signals from two stereo sources to two

SM Pro Audio's M-Patch ($179) is a passive volume control that works as a patch-control device for routing audio signals from two stereo sources to two stereo destinations. The M-Patch is intended to fill the needs of video and computer recordists, especially those who want to avoid using a mixer.

The metal casing is one rack-space high and slightly less than eight inches wide. You can place it on a tabletop or mount it using the supplied rack ears. The package comes with rubber feet and a pair of short female-XLR-to-female-TRS adapter cables.

All inputs and outputs are on the rear panel. The input labeled Stereo is balanced and has two combination XLR and TRS jacks. The input labeled Aux is unbalanced and has a stereo minijack and two RCA jacks. Two pairs of balanced outputs are on XLRs. The front panel has a switch to select the input source and another to mute the inputs. Two additional switches let you select the output and choose from mono or stereo output. Two attenuator knobs, calibrated in decibels, control the Stereo and Aux input levels.

A Switch in Time

For use as a simple stereo input and monitor switcher, the M-Patch is handy. You can connect two pairs of speakers for comparison purposes; you can also switch between speakers and a stereo line-level device or use the M-Patch purely for routing line-level sources. The two sets of inputs were perfect for listening to mixes from my recording rig (on the balanced XLR inputs) and to music from my home-stereo unit (on the unbalanced inputs). Although I use a hardware mixer for recording, I like having an alternate way to route audio to my monitors; when I just want to listen to a CD, I don't have to turn on the mixer.

As with many SM Pro Audio products, the M-Patch is aimed at the mixerless computer-based recording rig. Theoretically, such a rig lacks a method to reduce volume in the analog domain, and the user therefore has to either turn down faders in the digital domain or run the monitors at full tilt. The M-Patch provides the means to attenuate audio coming from the computer. Because many monitoring systems already have a way to control volume, however, that solution is useful mainly for owners of standalone active monitors.

The M-Patch's two input attenuators let you easily set comfortable listening levels. With no output attenuation, though, you can't adjust the comparative levels of two sets of monitors. Consequently, you might find yourself frequently adjusting the input-level pots as you switch between speaker sets. Although you might be able to set comparable levels between monitor pairs if your monitors or power amps have level-adjustment capabilities, how badly do you need a separate attenuator device if you can do that already?

The best monitor mixers offer the opposite of what the M-Patch provides: rather than input attenuation, they incorporate output-level trim controls for the individual speaker sets as well as a master output-level control. For a stripped-down box, a more logical and useful design might be to have the unit accept a line-level signal as is, and then offer attenuation at the outputs.

The sound of such a device is another crucial issue; the prime directive should be the complete absence of signal degradation. I set up a comparison test with one active monitor connected directly to my mixer and the other monitor connected to the mixer through the M-Patch (both of them balanced connections), and then sent a mono mix of a sustained loop through both channels. The M-Patch matched the direct signal pretty closely, but I did hear minor differences that wouldn't be obvious in anything other than a sustained A/B comparison. The differences, although extremely minor, were a slight reduction in bass and a slight change in high frequencies. I didn't hear any differences when using the unbalanced input.

Making the Switch

A useful monitor switcher lets you control input and output levels. There are other products that offer more control than the M-Patch, but they cost considerably more. That makes the M-Patch a viable choice for very specific recording setups, such as a system that has monitors with no level-adjustment capability, a system in which you need to switch between two stereo sources and two speaker pairs, or a system in which you need outboard mono summing. If you own one of those setups, the M-Patch could be right for you.

Overall Rating (1 through 5): 3
SM Pro Audio/Kaysound (distributor)