Mid/Side Processing Overview
The Beatles’ “Abbey Road” … Led Zeppelin’s “IV” …. Queen’s “A Night at the Opera” …. Michael Jackson’s “Thriller” are undoubtedly some of the greatest multi-platinum albums of all time. They also share a much less known commonality; they all used Mid/Side processing to create some of the most unforgettable sounds and audio imagery.
Mid/Side processing is a technique that has been around since 1930, but usage tracking on our Access Analog system shows that Mid/Side processing remains an underutilized tool for many people creating their own mixes. We think it’s because people don’t fully understand how to use this technique, so let’s demystify this tool and provide some basic examples.
Nerd Alert...The "What" Behind Mid/Side
It is tempting to skip this part, but you really need to know the “what” behind Mid/Side processing to use it effectively. Mid/Side processing is a technique used to manipulate the stereo image, and it’s actually straightforward; the “mid” channel contains the mono or center information of the recording, while the “side” channel contains the stereo information.
The channels are created using the following summing and subtraction:
Mid Channel = (Left + Right) / 2
Side Channel = (Left – Right)
To recreate the stereo pair, the process is reversed:
Left Channel = Mid + (Side / 2)
Right Channel = Mid – (Side / 2)
Here we have a nice visualization of Mid/Side processing.
This graphic shows a Left/Right Channel stereo sine wave converted into Mid/Side.
You can intuitively see how the amplitude of the channels changes as you pan from the left to the right.
The important takeaway from this graphic is that you can now manipulate both the center of the stereo image and the edges of the stereo image.
Great, so what can I do with that?
How about trying these three techniques that all audio engineers need to know:
- Adjusting the Amplitude
- Changing the EQ
- Using Compression
Adjusting the Amplitude
The Access Analog system has many innovative features; this is where you truly get something for nothing. Regardless if a piece of gear natively supports Mid/Side processing, we have the ability within our server to create the Mid/Side channels for you prior to the inputs on the unit. You can use Mid/Side processing with any stereo configuration.
Moreover, the Access Analog server provides free access to our two converters. Both the Galaxy and Lynx converters have a pair of loopback cables that loop the signal through the converter and back with no external processing. Anyone can use these loopbacks for free. So tee up one of your favorite stereo mixes in your DAW and grab your best headphones.
Setup your Access Analog rack as shown below. You will need to enable the Mid/Side processing and disable the Link button for the L/R input gain shown in green circles.
Once your rack is configured, increase and decrease the L/R gain controls relative to each other and feel how the image shifts from the center to the edges. Think about how you might use this to increase the power of the main vocals by increasing gain on the Mid channel.
Conversely, you can reduce the Mid gain and increase the Side gain on the background vocals to widen the image and create more surround. This is a simple but very powerful tool.
Changing the EQ
Now that you have experienced the amplitude adjustment with Mid/Side, let’s experience the most common use of Mid/Side processing with the addition of EQ. Combining Mid/Side processing with an EQ allows you to optimize the placement of sounds in the stereo image.
For example, you can isolate the high frequencies of the drum cymbals and move them all the way out to the sides so they don’t distract from the other instruments in the middle. Find a favorite stereo track that includes drums with hi-hats or cymbals, and open your DAW.
Load up your rack with the API 5500 and Mid/Side enabled. Make sure to set the Link L/R to None.
This is important so you can make independent changes on the EQ to the Mid(Left) and Side(Right) channels. Experiment with increasing the gain on the high-frequency shelf on the Side(Right) channel and decreasing the high-frequency shelf on the Mid(Left) channel.
Depending on what instruments and frequencies you have on your mix, play around with moving instruments and vocals around the stereo image to widen the sound or focus the punch of one instrument.
Saving the most fun for last!
Using compression with Mid/Side channels lets you control the dynamics for the Mid and Sides of a mix separately by using their own ratio, attack, and release settings. Think of it as a multi-band compressor on steroids.
For this experiment, let’s use our Chandler LTD-2 compressors; they are very straightforward, very clean, and very vintage. Load up your DAW with a song with strong guitar sounds, and then configure your Rack as shown in the image below.
Note that each Chandler is a mono device, so use the Dual Mono menu item to pull both Chandlers into your rack for stereo processing.
Again set the Link L/R to None and the to Enabled. Note the “View: L and R buttons below the chandlers. The L and R buttons allow you to select the compressor assigned to the Mid(L) and Side(R) Channels.
For the first experiment, increase the gain on the Mid channel slightly and then set the left channel’s attack and release to slow. Notice how the guitar in the center has less bite; it is smoother and less harsh.
Conversely, you set the attack and release to a fast setting and pump the channel so that the guitar grabs your attention and asserts itself into the sound experience.
With those three techniques, you have all the basics you need to know to get started with Mid/Side processing. If you’re feeling really comfortable, try all three tools together with a chain of the API 5500 and Chandlers, and use the input gain sliders for amplitude adjustments. It’s a powerful combination; with some experimentation, you’ll be able to create some powerful stereo images. Have Fun!