How to Use Stereo and Panning in Video
Just like we have two ears on our head, most audio setups put two speakers in front of us, making a stereo setup, as opposed to a one-speaker mono formulation or a multi-speaker surround sound rig.
Stereo sound works quite simply – if a sound is heard louder in the right speaker than it is in the left, it will appear to be coming from the right-hand side; if the two speakers play the sound at the same level, it will appear to be coming from the center. These level adjustments are a fundamental part of audio mixing and are handled by a Pan control – whether it’s a physical control on an audio mixing board, or a virtual one in a DAW or NLE.
While the basics of stereo and audio panning techniques are simple, once you dig deeper into stereo, there’s a lot more to understand about how it works, and even why it works.
With a two-channel stereo setup and pan control, when mixing audio we can use audio panning to choose which speaker plays a particular sound louder, and by how much. But the point of stereo isn’t just to have sounds flying back and forth around the listener’s head – it’s to create an immersive virtual sound stage between the two speakers.
If you sit between two speakers with a sound centred, it’s easy to distinguish where it’s coming from. As the sound moves to the left or to the right, you can probably point to where the ‘phantom image’ is coming from, even with your eyes closed. As we’ll find out later, our brain is remarkably good at determining where sounds are coming from in space, and the audio process behind panning audio works to match it.
If you sit between two speakers, listening to a really great, modern song, it’s likely you’ll be able to point to the exact place where each instrument sits between your two speakers. Thanks to the modern audio panning techniques behind music mixing, different elements will have been panned to different points, helping to separate each one in the ‘virtual sound stage’. For audio mixing, this kind of virtual sound stage separation is crucial, but for video work, there are more principles too.
Stereo audio allows video makers to immerse their audience in a three-dimensional world of sound. By using two separate audio channels, one left and one right, we can experience the illusion of actually being in the space where the audio was recorded. When we are listening to the real world, each ear picks up slightly different sounds, in the same way the two audio channels of a stereo audio recording will also vary slightly.
The stereo field can also be used by video makers to easily position people and objects in space. In NLEs and DAWs, audio channels have pan knobs which determine where in the stereo field a sound is placed. If you want to give the illusion that a person is speaking to your left, you would turn the pan dial on their dialogue channel to the left. This will turn up the left audio channel and turn down the right one. The image below shows the relation between the pan knob and where the sound is positioned in the stereo field.
If you hard pan (pan something all the way to the left or right) a sound, then this isn’t technically using the stereo field. A voice hard panned to the left will only come from the left speaker, no sound will come from the right. In this case the sound is actually mono as you’re only hearing a single sound signal.
Positioning sounds in space is important, but so is positioning them in time.
When it comes to using the stereo field in your own videos, there’s a lot of room for creativity. Ambient sound in film such as crowds, traffic and nature always benefit from being in stereo. Though foley sound will rarely be at the forefront of your audio mix, they are key for creating immersion, putting your audience right in the middle of the scene.
You can elevate this experience by adding occasionally panning audio SFX for extra emphasis. For example, in a scene set in a busy street you may have a stereo ambient street recording playing in the background of your scene, but for a bit more bite you could add a few panned horn honks and engine noises just to sell the setting a little more.
Check out a single scene built piece by piece for realism with sounds from our SFX Cellar platform in our Scene Sound Design tutorial.
Sound effects such as gunshots, punches and explosions (all the good stuff) that need to hit hard will have more impact if they’re set in the center of the stereo field. Of course, as with all creative processes, this isn’t a one-size-fits-all rule. An offscreen gunshot or stylised martial arts fight may benefit from a little panning if the implication is that the action is happening on one side of the screen.
Panning dialogue is a source of much debate. Old-school wisdom is that all dialogue should be mono and down the middle, this gives clarity to the most essential part of your video, and helps keep it reliable between playback systems. Overly panned dialogue can be distracting and actually take the viewer out of the experience of watching your video.
However, some argue that there is room for panning dialogue in videos if a character is off screen or walking across the frame. This is your call but, if you do decide to pan dialogue, be subtle. Don’t pan voices more than 15-20% left or right, as beyond there it really does get distracting.
You might have two speakers, but it doesn’t mean you’re automatically working in stereo. If all audio is perfectly centred between two speakers (ie, every pan knob is at its middle position), the effect is a single source of sound between the speakers.
As you can see the audio is split into two separate channels: left and right. Each of these channels on its own is mono – and if the signal in each is identical, the resulting audio would actually be mono, even with each channel played via a separate speaker. It’s the difference between the left and right audio channels that makes audio stereo.
Of course panning sound effects that are mono gives the illusion of the sound being placed in the stereo field. As soon as the response is different between the two speakers (in this case, one plays the information louder than the other), we’re in stereo territory.
Can Your Microphone Record in Stereo?
Stereo microphones do exist, however most stereo recording is actually done using multiple microphones.
Figure-of-8 microphones can often incorrectly be thought of as stereo microphones due to their double-sided pickup pattern.
However, despite the fact that figure-of-8 mics pick up sound from two directions, they do not record a stereo signal. Instead they output a mono signal that has been created by movements of both positive and negative regions.
Multiple mono mics are normally used for stereo recordings. This is because the key to creating the stereo illusion is in having differences between the left and right channels. Therefore it’s important to position the two mics slightly apart.
Stereo microphones do exist. Like the Rode NT4 or Zoom’s H4n, these have two capsules positioned close to each other. They’re great for recording stereo audio ambience, however if your sound source is positioned directly in front of the mic, the close proximity of the two capsules will mean that the recording is closer to being mono – there simply won’t be enough difference between the left and right channels for the audio to be dramatically stereo. So if you want wider ambience audio move your mic away from your sound source!
It’s time to get technical, let’s dive in and get to grips with how stereo audio tricks our brain into perceiving two audio channels as a 3D space.
In the real world our brains work our the direction a sound is coming from using Interaural Time Difference (ITD) and Interaural Intensity Difference (IID). Though these sound a little complicated, really they’re very simple concepts to get to grips with.
ITD is the slight delay between a sound arriving at one ear and then the other. Though we aren’t really aware of this difference, our brain picks up on it and uses it to locate sound sources around us. The more to the right of us a sound source is, then the greater the difference in time between the sound arriving at our left ear compared to our right ear will be.
IID is much the same however, as the name might suggest, it’s the difference in the intensity of a sound in each ear that our brain is using to work out the position of the sound source - it's responsible for the feeling of audio ambience.
The pan knob on your video editor’s mixer takes advantage of IID’s intensity difference rather than ITD’s time difference. By panning audio left or right, you alter the volumes in the left and right speakers effectively changing the intensity of sound reaching each ear.
- Real Stereo Recording
So now we know how stereo recordings work on a technical level, let’s run through setting up a basic mic arrangement for creating your own stereo recording.
Here we’ll run over the most basic of stereo mic setups: the XY stereo ‘coincident pair’ configuration.
1. This technique requires two cardioid mics and two mic stands. Two identical microphones are preferable here, to avoid any difference in different microphones’ frequency responses.
2. Set the mics so their capsules are directly vertically aligned and recording horizontally perpendicular to one another, as in the below image. The sound source should be on the 45 degree angle directly between the two mics
3. Record your sound source.
4. Load the two audio tracks in your NLE or DAW and pan the audio recorded with the right-hand mic to the right and vice versa with the left-hand mic.
5. You now have a stereo recording. If you want to create a single stereo audio file then you can bounce these two tracks down into one track.
- Converting Stereo to Mono
Converting stereo to mono is fairly simple, and most NLEs and DAWs will have some kind of option for this in their export window. The big advantage of mono is that everyone hears the same signal, no matter how their setup is constructed or where each listener is located.
People listening on certain devices – including some phones and lots of bluetooth speakers or other lower-quality gear – may be listening to media in mono rather than stereo. In these cases, your stereo signal will be converted to mono by each device.
This may not be how you intended your work to be experienced, but this is the reality of different methods of playback. To ensure your mono-ized audio is being reproduced as you expected, it’s worth checking your work in mono before committing to your final export, in case any elements are misrepresented or disappear.