Don’t Forget About Sound!

Why is Sound Important?

One of the biggest technical deficiencies most filmmakers I’ve ever met and worked with seem to have is audio.

Speaking as someone who started his career as a composer and music editor, this is one area of production that gets almost entirely overlooked in film schools, and it’s a shame.

Most people go into filmmaking just don’t care all that much about sound — and I get it, they tend to be driven by visuals and writing, and tend to think that those are the only really essential elements of the medium. Plus it’s harder for people who aren’t musicians or who are otherwise not used to carefully listening and analyzing sounds to differentiate between good and bad audio. So it seems to me that between the technical challenge of the work itself and the general lack of interest by filmmakers themselves, audio simply gets ignored.

And yet, sound is a massively important part of the filmmaking and film-viewing experience.

Think about your own experiences as a viewer. I would bet that you are far more willing to tolerate a short film or YouTube video that has mediocre lighting, poor quality color representation, bad set design or costumes, lower frame resolution, or anything else that degrades the visual quality of the experience than you are willing to tolerate bad sound.

In fact, bad sound is not merely a potential distraction. It can literally be a painful experience.

Imagine trying to listen to a film with a high-pitched whine or aggressive static that carries through the whole audio experience. Imagine spending an hour trying desperately to hear dialogue that hasn’t been recorded, mastered, or mixed properly. Imagine putting up with random spikes in dynamics that force you to keep a hand on your volume knob to avoid blowing out your eardrums whenever the sound decides to take a random detour into the 120dB range.

We both know that you won’t tolerate any of that. Instead, you’ll just change the channel or close your browser tab.

And everything I have talked about so far comprises merely the minimum standard of quality the sound quality of your film must meet.

Great sound design can elevate a film into the stratosphere of movie-going experiences.

Think about a movie like Gravity.

Or Star Wars. Apocalypse Now. Saving Private Ryan

These are films that use sound to radically enhance the experience of the stories they’re telling. They put audiences inside the minds of their protagonists. Inside the scenes themselves. They use sound to compel the viewer to feel something they would never feel with imagery alone.

What’s more, carefully constructing the sound effects of a film is also one of the most powerful tools available to editors in terms of controlling information — listen to the way sound is used in great classic horror films like The Shining or The Omen, and in modern films like Don’t Breathe to really get a sense of what I mean.

Good sound can heighten tension or calm an audience. It can obscure dialogue or bring it into focus. It can help us bridge from one scene to another by smoothing over hard cuts or it can be used to jar the audience from one scene to the next.

Even if you’re not planning to make a career of audio production and sound design, it's still worth knowing a few things about how it works so that as a filmmaker and editor, and as a storyteller in general, you’ll be better equipped to make good artistic choices and elevate the quality of your work.

With that in mind… Let’s begin with the basics and take a look at the tools audio producers use to record and edit sound.


Understanding Microphones

In my experience, filmmakers have a pretty good understanding of cameras and lenses, some expand that understanding into lighting and grip technology. Very few understand even the basics of microphones. So I think it’s important to start at the beginning and take a look at the difference between different kinds of equipment.

Types of Microphones

These are two of the main types of microphones we use on a regular basis, and while they have different end-uses, the biggest differences between them is actually how they function.  

A dynamic microphone has a physical rubber/plastic diaphragm stretched out over an electromagnet. As the diaphragm vibrates, that pushes an induction coil into the magnetic field of the magnet, which (as of course we all already know from Faraday's Law) induces a voltage into the coil, which then transfers down the cable to the mixing board.

See the diagram below:

dynamic-microphone.png

What's important to understand here is that this is effectively a passive process - the induction coil creates its own electrical signal, so it doesn't need an external power source.

By contrast, a condenser microphone works a completely different way. two parallel metal plates are fitted next to each other forming a capacitor, with the outer plate acting as the diaphragm of the microphone. As the diaphragm plate vibrates, it touches the back plate and closes a circuit, thus generating an electrical signal - which, again, then transfers down the cable to the mixer.

See the second diagram.

condenser-microphone.png

For this to work, there must be an active power source connected to that circuit, so that's where Phantom Power comes into play.

Some condensers have to have a battery to supply the necessary power to create the circuit. I still own a few that need this. But most modern condenser microphones are now able to draw power through a mixing board via 48-volt Phantom Power, which runs through the XLR cable to the microphone (when turned on). 

Though I’ve focused on two types of active and passive microphones, there are actually a ton of other ways to record sound.

Basically any way of taking a vibration and converting it into an electrical signal can be used to create a microphone. In addition to magnets and wires, this includes quartz crystals, lasers, and fiber optics. 

And each microphone has a different a slightly different way.

Pick-up Patterns

Different microphones are designed to record sound over different distances and different kinds of area shapes. Some microphones will pick up sound all around them while others will pick up sounds only form one direction. Some (like shotgun microphones) have a long and narrow range; others have a shorter, more rounded pick-up range. 

Different recording needs require different patterns. See the diagram below for a basic depiction of different types of patterns.

pickup-patterns.png

Understanding pick-up patterns is important because it will play a huge role in mic choice and placement depending on what you want to accomplish. Generally speaking, you’ll see dynamic cardioid or super-cardioid microphones like the Shure SM58 used by singers in live sound environments. You’ll see omnidirectional or bi-directional condensers used to record classical or acoustic performances in concert halls and other large rooms. And of course you’ll see shotgun microphones (not shown) used by filmmakers to capture a narrow band of sound at a distance.

Every microphone and every pick-up pattern has different characteristics, and each can help us capture excellent sound recordings across various environments and challenging circumstances.

Phantom Power

Remember that some microphones require electrical power in order to function. The way most (not all) microphones get the electrical current they need is called “Phantom Power”

Phantom power (which you will normally see represented on a sound device as “+48V”) is a way of transmitting electrical signals through the microphone cable itself — as opposed to microphones that have separate power supplies (ie. batteries or ballasts).

It's one of the more important things everyone needs to know about audio recording, and is responsible for one of the most frequent and most basic I/O errors people make. If you have a microphone plugged into your mixer or camera, and there's no signal coming in, it's a good idea to first check whether or not Phantom Power switch is turned on.

Microphones that need Phantom Power are (as far as I know) exclusively condenser microphones (like the Genesis II, Rode NT2-A, and many lavalier microphones).

Cables: Lo-Z vs. Hi-Z

On a related note, not every type of microphone cable is well-suited to carrying phantom power, so if you’re having trouble getting signal from one of your active microphones, checking the kind of cable you’re using is another important troubleshooting step.

"Z" refers to a cable's level electrical impedance

This is where my lack of being an electrical engineer makes me a lot less able to fully understand or explain what this is all about, but I'll do my best.  

Fairly obviously, Hi-Z = high impedance, and Lo-Z = low impedance. 

What this means for us is that a Hi-Z cable actually transmits a high voltage but low amperage signal and a Lo-Z cable transmits a lower voltage, but higher amperage signal. 

This essentially makes Hi-Z cables very good at transmitting a strong signal because there's a lot of electrical pressure/tension (ie. a lot of electrons are being forced into the circuit). However, higher impedance limits the total amperage, so that the electrons are traveling through the circuit more slowly, which means that the stronger signal cannot travel that far. 

What this means for audio is that a high impedance cable will help boost the loudness coming into the mixer, or out to a speaker (more electricity in the circuit at once), but it will be worse at carrying that signal out over long distances (for our purposes, over 15-20'). By contrast, Lo-Z cables are better for carrying a signals over very long distances, but need a lot of amplification in order to reach their destination audibly.

As a rule of thumb: 

  • Lo-Z is what we need to run a speaker cable across a ballroom, but needs to be amplified

  • Hi-Z is what we need to get a good signal to a mixer from a microphone/instrument over a short distance without driving up the gain on the mixer.

On a side note, most Hi-Z cables are instrument cables. The ones I can find now that will support microphone inputs mostly connect mono TRS (tip-ring-sleeve connectors like you need for a guitar) to XLR. 

Very few XLRM-XLRF cables seem to even be available as Hi-Z at all anymore. It also seems that this is mostly an artifact of consumer preferences more than a technical requirement. But they do still exist and it’s always a possibility that you’re using the wrong kind of cable over an inappropriate distance if you’re having problems getting the signal you need.

Rather importantly, a high-impedance microphone cannot work with Phantom Power at all, and a Hi-Z microphone cable will not carry that power very far.

So... While you can use Phantom Power with either type of cable, it is the Lo-Z cable-types that are better for use over any distance greater than a few yards. That's not only true for sending Phantom Power to a condenser microphone, but more importantly true of sending signal from any microphone back to a mixer or for sending signal from a mixer to speakers a great distance away.

Since wired lavalier microphones are typically condensers and don't have internal batteries, they need Phantom Power. 

In the majority of applications, this has never been a problem and all we need to do is make sure Phantom Power (48V) is enabled on the camera microphone settings. On camera systems like the Canon C300 or Sony FS7, it's just a switch next to the audio input controls on the handle. On most mixing boards, it's also a simple switch near the master output ports.


Audio Mastering & Mixing

[Coming soon]

Sean MaloneComment