Avenson Audio: Blend mixer, Mid-Side matrix

If you do any audio processing in the analog domain, whether you rely on a large-format console or just a modest rack of gear, you'll realize quickly how powerful and easy-to- use these half-width, 1RU-height tools from Avenson are when you plug them in. Plus, you'll appreciate how they do what they do transparently, without adding any sonic character of their own. The names of these units pretty much tell you what they are. In simple terms, the Blend is a two- source stereo mixer with a crossfader to choose one source or the other - or a blend of the two. And the Mid-Side is a double-ended M-S matrix that allows you to convert a stereo signal from standard left/right mode to mid-side mode and back. Why would you want to do either of these things?

Let's start first with the Blend. Yes, it can blend two unrelated sources, but really it was designed to facilitate parallel processing of a single source. On the front is the aforementioned crossfader. At the left end of its 100 mm horizontal path, it's labeled Dry, and at the right end, it's Wet. On the back are stereo pairs of balanced 1/4'' TRS jacks - Dry In, Dry Out, Wet In, Mix Out. The premise is that you'll hook up the source you want to process into Dry In; loop a copy of it from Dry Out to some outboard processor and back into Wet In; and use the crossfader to mix the unprocessed and processed signals together. Mix Out will then feed whatever is your next downstream device.

I imagine by now that most of us are familiar with parallel compression - blend the uncompressed signal with the compressed (and often "overcompressed") signal. This technique allows you to level out a track or subgroup, or bring up the sustain of a recorded instrument, while still allowing the dynamics of the original recording to come through over the top. The effect is often described as making something sound "bigger" without making it sound "lifeless." Whenever I compress drum stems, for example, I use parallel compression, so that the drums really bloom and the ambience of the room surrounds the drums, but the individual drum strikes still punch through - very simple to do using the Blend.

But you can also use the Blend for parallel EQ. Due to the phase shift imparted by analog EQs, mixing dry and EQ'ed versions of a signal together can lead to some happy accidents, especially in terms of how the frequencies at the edges of the filter bands interact. With heavy-handed parallel EQ'ing, resonances and cancellations can appear where you might not expect them, and sometimes you get focus while other times you get blurring, depending on the complexity of the signal you're EQ'ing.

For vocals, I almost always use a combination of parallel compression and EQ. One of my go-to tricks is to band-limit the vocal severely with an EQ or filters, and then compress it until it's sounding like it's coming out of an AM radio or old- school telephone. Then I blend a wee bit of that with the unprocessed vocal and follow with broadband leveling. This makes for a very steady vocal that can stay planted even in the midst of a complex mix, while still retaining much of the dynamics and character of the actual performance. Most singers who hear their voice this way ask me if they can take this sound home with them! Well, with the Avenson Blend, a filter/EQ, and a couple compressors, it's actually straightforward to implement.

There are two more elements on the Blend's front panel worth describing. First is a switch that flips the polarity of the Wet In signal. This feature is useful if one of your processors is improperly wired or if you're trying to achieve some form of cancellation. But it's also great for parallel EQ, and here, the results aren't always what you think they'll be; your analog EQs will take on a whole new life! The second is a large, 16- segment (per channel) stereo LED output meter that's especially handy for parallel compression because its ballistics seem optimized for understanding how your process affects the final dynamics in the blend.

Now let's discuss the Mid-Side. On the front is a stepped rotary switch labeled Width and a potentiometer for a low- pass filter. On the back are stereo pairs of 1/4'' TRS jacks that implement the following signal path: L/R In, which is converted inside the unit to a mid-side signal; Mid/Side Out, which you patch to an outboard processor of your choosing; Mid/Side In, for the processed return, which is converted back to left/right mode; and L/R Out, which feeds the next downstream device in your chain. If you leave the Mid/Side connections unpatched, they're internally normalled, and you're limited to the use of the Width and LPF controls on the front of the unit to effect the signal. Changing Width does exactly what you'd expect it to do; you turn the knob to emphasize the mid content or the side content. The LPF operates on the side content, allowing you to take out lows that might pull your ears (or a stylus on a vinyl cutter) to one side; in essence, it makes the lows sound "more mono." Both of these functions are useful, but things get really fun when you patch in an outboard processor.

For example, I'll patch a program compressor, like my API 2500 [Tape Op #52] or Safe Sound Audio Dynamics Toolbox [#64], in serial with an EQ through the Mid-Side across a stem bus or the mix bus insert. When I process the mid and side channels like this, centered elements in the mix stay centered, without jumping left or right during heavy compression. Also, I can squeeze the mid channel while still retaining a healthy bit of dynamics in the side - or vice versa. In conjunction, I'll use parallel compression by incorporating the Blend, giving me even more control over the dynamics and feel of the stem or mix. I also use M-S processing with reverbs. For example, I'll feed a vocal track to two different effects, and then go through one end of an M-S matrix on the return, throwing one effect straight up the middle and the other effect onto the sides. My main Zerotronics CoolSprings reverbs [#55] were custom-built with different decay times for their two channels, and M-S decoders on their outputs, just for this purpose. But the Mid-Side allows me to do the same thing with other effects units. And one trick I learned from mastering engineer Jeff Lipton [Tape Op #34] is to use a de-esser or multiband compressor to remove sibilance from centered elements in a mix (like vocals) or harshness from the sides (like overbaked cymbals).

Moreover, you can use the Mid-Side to unravel mid-side recordings. For example, one of my favorite methods for recording piano is to set up a cardioid mic pointing into the piano, and a figure-8 mic sideways, directly above or below the cardioid. When I want to convert these tracks to standard stereo mode, I go through one-end of an M-S matrix. On the Mid-Side, I can use either the L/R to Mid/Side connections, or the Mid/Side to L/R connections.

I'm sure many of you have already incorporated parallel and M-S processing into your normal workflow and are wondering why you need these Avenson boxes, when both techniques can be implemented with faders and polarity switches - whether in software or on a real console. Well, any time you play with digital faders connected to analog devices, you have to think about conversion latency; the Blend and Mid-Side exhibit zero latency. Plus, with the Avenson units, you can place your parallel or matrix process in the middle of a multi-device chain, not just at the beginning and end of your analog chain if you're relying on a software mixer. And compared to an analog mixer, each Avenson box has a much simpler signal patch that's optimized for a singular purpose, and therefore, each imparts far less distortion than console faders and buses do.

It's clear to me that recordists relying on analog outboard processing can really take their game to the next level by adding the Blend and Mid-Side to their kit. Like other Avenson products, they're well thought out and built tough. A 1RU-height, full-width rack shelf can be purchased separately to rackmount two of these units side- by-side. To learn more about Brad Avenson, read his "Behind the Gear" interview in Tape Op #76. (Each $600 street, rack shelf $45; www.avensonaudio.com)