What a sound engineer hears

Before we start, can we all be silent for thirty seconds? I need to record the room.

This is Room Tone, and that request is where our name comes from. I'm Tomás Reyes. My guest is Sam Okafor, a location sound recordist who works on films and documentaries.

Thirty seconds. Nobody moves.

So explain what we just did.

Every room has a sound, even when nobody is talking. The fridge, the traffic, the air in the vents. It's different in every room and it changes through the day. When an editor cuts a conversation, they remove coughs and pauses, and that leaves holes. If you fill a hole with digital silence, it sounds like the world switched off.

So you fill it with the room's own quiet.

And you record that at the start of every scene?

Every setup. Same mic, same position, same people standing in the room, because bodies absorb sound too. Editors remember the recordists who give them room tone, and they curse the ones who don't.

How long does a recording of silence need to be?

Thirty seconds is the minimum. A minute is generous. Editors loop it underneath the cuts, and if it's too short, you can hear the loop, like a clock ticking in the wrong place.

What makes a room bad?

Hard, parallel walls. Glass, tiles, a kitchen with nothing soft in it. The voice bounces back and forth and arrives at the mic twice, a little late. It sounds hollow. You can't really fix that later.

So what do you do?

Move. If I can, I ask to shoot in the bedroom instead of the kitchen. Beds, curtains, clothes. A wardrobe full of coats is the best studio in any house. If I can't move, I hang blankets just out of shot and get the mic closer.

What's the worst room you've worked in?

A church with a fridge in the vestry. Beautiful echo, and a hum at fifty hertz under everything. We found the plug, and the priest let us switch it off for two hours, as long as we promised to switch it back on. I wrote it on my hand.

Do people ever notice you on set?

Only when something goes wrong. If I do my job well, nobody remembers I was there. The actors remember the camera operator, and they remember the person who brought coffee. The sound recordist is the one standing in the corner with headphones, looking worried.

Are you worried?

Always. A picture problem you can see on a monitor. A sound problem you might only hear in the edit, weeks later, when it's too late to go back.

What's in your bag?

Less than people think. A shotgun mic on a boom pole, two small clip-on mics, a recorder, good headphones that fold, and a lot of spare batteries. Then the unglamorous things: gaffer tape, a soft furry cover for wind, and a notebook.

A notebook?

For the sound log. Every take, what went wrong, a plane at twelve seconds, a door slam. The editor reads it months later. It's the most useful thing I make, and it's written in pencil.

Sam Okafor, thank you.

Thank you. And now, everybody, thirty seconds of silence for the editor.

That's Room Tone. Next week, Ada spends a night in a café at the ferry port.