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How to Manipulate the Stereo Field of a Mono Source


Hey folks, Matthew Weiss here:, Gonna take a little bit of a turn and discuss a string recording and engineering practice that I did recently. It’s kind of cool, and this can be applied to other instruments as well but I just so happened to do it on a solo viola. I wanted to give the viola some stereo spread because of the way it was going to live in the mix. I didn’t want it to necessarily have that strong central mono compatible sound that’s important for a lead. I wanted something more that was gonna fill out space. So, what I did was I recorded the viola with two microphones side by side, and I chose microphones that were very different in terms of tonality. So, the first one was a condenser and it sounded like this:

[viola + condenser microphone]

And the other was a ribbon and it sounded like this.

[viola + ribbon microphone]

And you can hear that the texture of the top-end of the ribbon is a little bit brassier, and there is more fundamental tone coming through in the ribbon, whereas the condenser it’s a little bit more of that presence range. A little bit more open sounding. So, they sound different. And here’s what they sound like when they’re summed together.

[strings + ribbon & condensor microphone summed]

So, they’re very close together so there’s a little bit of a phase thing going on in addition to a frequency thing going on. And that’s what’s creating the change in tonality. Now, it’s not a dramatic change in tonality, but it does add a little bit of depth and take away a little bit of solidity.

Anyway, here they are panned apart.

[strings + ribbon and condensor microphone panned apart]

And you’ll notice that on different notes and at different parts, the weighting of where the viola lives seems to move around in the stereo field. Which is kind of cool, it’s almost like sort of a frequency dependent auto-panner in a way. And what we’re gonna do is use that to our benefit to create a very wide big sound from this single viola.

So the first thing I’m gonna do here is I’m going to pull up the FabFilter Pro-Q. One of the things that’s cool about the FabFilter Pro-Q is that you can not only do a traditional left and right equalization on it, you can also do mid-side equalization. And so what I’m going to do is i’m going to boost up the mid tone — the mid signal fundamental. And it sounds like this.

[viola + mid EQ boost]


[viola + mid EQ boost]

And back down. So what it is is the movement on the side, the different in the side is not really changing so much but the mid tone I’m giving more weight. And the side tones, I’m going to give that harmonic presence energy up around the 1k zone. That’s sort of where you hear the floaty glowiness of the tone. And that sounds like this.

[viola + side EQ boost]

So before. After. So if you’re wearing headphones you’ll definitely notice that difference, but even in speakers I think you can notice it subtly, what you really hear is you hear that movement of the frequency energy a little bit more pronounced. Which is basically what I wanted. The other thing I’ve got going on here is I’ve — there’s also a mid-side function on this, when you switch into mid side mode, you can lean the side weighting so I have it leaned a little bit more so that the sides are a little louder relative to the mid, and then in response I’m turning up the overall signal because it spreads it out, it doesn’t just gain the sides laterally. So, anyway, here’s the before and after of the whole equation.

[viola with and without mid-side EQ boost]

And you know I’m big on things that don’t necessarily sound dramatically different but give a life and energy to something. The recording was basically good sounding to begin with. I don’t really need to do much to the viola, but by doing these sort of subtler tweaks, you don’t hear a huge difference but you definitely feel a lot more life pop into the string capture.

Alright, so the next thing I’m doing is I kind of like the brassy texture that’s happening in the — from the bow hairs. So that like super treble thing that’s going on. What I’m doing is that can become very piercing and overwhelming if you just pump the treble up, so I’m using a multi-band compression, again Fab Filter Pro-MB. And What I’m doing is I’m using the compressor so that when there’s a lot of treble information in the strings, there’s no gain to the treble because it’s bringing the gain back down to a neutral position. But as the treble starts to die off, then the compressor begins to release and the gain on the treble that I’ve set starts to show up. And so you end up with a more consistent treble sound and ultimately as a result, the bow hair sound becomes more obvious. So here’s a before and after.

[viola with and without multiband compression]

One more time.

[viola with and without multiband compression]

And you may also be noticing that there’s a little bit more extra movement in the treble range going across the stereo field. That’s because a little secret under the hood here is that the FabFilter Pro MB has this band split stereo imager. Which is really cool. Basically what it does is where you’ve split the frequency band, it can then adjust the stereo perception of just that individual band, so what I’m ultimately doing is I’m pulling the mid down on the treble, and using the output to compensate. So in other words I’m boosting the side treble information, not the whole side, but just the treble. Which, again, helps to sort of increase that sense of movement without necessarily screwing around with the fundamental tone of the viola.

Alright guys, I hope you learned something from that. These are techniques that you can apply to any mono instrument: guitars, you know, whatever. The idea is to use two microphones that are side by side and to then exploit the differences in those microphones by using mid-side techniques and equalization. It’s not something that I would necessarily do on anything that needs to have a focused compatible mono center, but it is something I would do if I wanted a stretched out stereo field. Alright guys, til next time.


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Matthew Weiss

Matthew Weiss

Matthew Weiss is a Grammy nominated and Spellemann Award winning audio engineer from Philadelphia. Matthew has mixed songs for Snoop, Sonny Digital, Gorilla Zoe, Uri Caine, Dizzee Rascal, Arrested Development, 9th Wonder, !llmind & more. Get in touch:
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