Noise Floor, Room Tone and Clean Speech: Audio Terms Explained
Fiona MacLeod explains the audio terms heard in every gallery, from noise floor to room tone and reverberation time, and why each one matters for speech and live music on air.
FM
Fiona MacLeod
5 min read
Why the vocabulary matters
Most arguments in a gallery about sound come down to two people using the same word for different things. A presenter says the room is dead, the engineer says it is controlled, and both are right in their own way. Over the years at flairuni I have found that a short shared vocabulary saves more rehearsal time than any piece of equipment.
This article takes a handful of terms that come up when we treat a room or set up microphones for speech and live music, and explains each in plain words. None of them is difficult. They simply sound technical when nobody has said what they mean.
If you are planning a bulletin set, an interview corner or a small stage in a venue, these are the words your audio engineer will use, and knowing them lets you ask better questions before work begins.
Noise floor: the hiss you stop hearing
The noise floor is the level of unwanted sound that is always present: air handling, the hum of lighting power supplies, distant traffic, and the electrical hiss of the equipment itself. Everything you want to broadcast has to sit comfortably above it, otherwise the quiet moments of a conversation are lost in background wash.
A low noise floor gives a mixer room to work. A high one forces you to turn the presenter up, and every other sound rises with them. Often the cure is not better kit but switching off a noisy extractor fan for the duration of the programme, or moving a rack of equipment out of the studio into its own space.
We usually measure the noise floor before anything else, with the room as it will be on air, because the number tells us how much treatment is realistic.
Fans, fridges and projectors are the usual culprits
Measure with the room set up as it will be on air
Reverberation and why a bare room sounds wrong
Reverberation is the persistence of sound after the source has stopped, caused by reflections from walls, ceilings and floors. Reverberation time is how long that tail takes to fade away. A hall with a long tail can flatter a choir, but it smears speech, so words blur into each other and the viewer strains to follow.
In a television studio we want the tail short enough that consonants stay crisp, yet not so short that the room feels airless and the presenter sounds as if they are speaking into a cushion. Absorbent panels, heavy curtains and soft furnishings on the set all shorten the tail, and where they go matters as much as how many there are.
Hard floors and large glass areas, both popular for modern news sets, are the surfaces we most often have to compensate for.
Room tone and the pause that sounds empty
Room tone is the sound of a space when nobody is speaking. Every room has its own, and it is the reason a silent pause in a live programme still sounds like the same place rather than a dead line. Editors in post production record thirty seconds of it for exactly this reason.
In live work you cannot patch a gap afterwards, so the tone has to be consistent from the first second. If a microphone is closed when someone stops talking and the background suddenly vanishes, viewers hear it as a drop-out even if they could not say why.
This is one reason we prefer to set gentle gating and sensible fader moves rather than muting channels abruptly, and why we ask guests to remain seated and quiet during breaks, not to walk across the set.
Proximity, pick-up pattern and placement
Proximity effect is the boost in low frequencies you get when a speaker moves close to a directional microphone. Used well, it gives a warm, full voice. Used carelessly, it makes a presenter who leans in sound boomy and one who leans back sound thin, and the mixer spends the programme chasing them.
The pick-up pattern describes where a microphone listens. A cardioid hears mostly in front and rejects the sides and rear, which is why it is the usual choice for interviews where two chairs sit near each other. An omnidirectional capsule hears everything evenly, which suits a lavalier but exposes every room problem.
Placement is where craft shows. A few centimetres of distance, a slight angle off the mouth to soften breath sounds, and keeping the microphone out of the shot and out of the lighting shadow are all decisions made before the programme starts.
Cardioid for interviews with chairs close together
Angle off-axis to reduce breath and plosive sounds
Headroom and gain: leaving space before it distorts
Headroom is the margin between the level you are running at and the point where the signal distorts. Live television is unforgiving here because a laugh, a cough or a sudden drum hit can arrive without warning. If the level is set too close to the limit, there is nowhere for the peak to go.
Gain is how much a microphone signal is amplified at the start of the chain. Setting it properly means asking the loudest person to speak at their loudest during rehearsal, then leaving a sensible margin. Setting it by guesswork means riding faders all programme to hide a problem that began at the preamp.
For live music the same idea applies on a larger scale. A band that sounds modest in the soundcheck will not stay there once the audience arrives and the drummer stops being polite.
None of these terms is a barrier once someone has said what it means. Noise floor, reverberation, room tone, proximity, headroom: each describes something you can hear for yourself in an empty studio if you stand still and listen. If you are planning a set or a stage and want to talk it through in these words, ring the team in Inverness and we will go through your room before anything is bought.
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flairuni plans and runs live television production from Inverness: studio integration, cameras, sound and lighting for news, interviews, concerts and festival stages.
