Room Tone: What It Is, How Long and How Loud

The short answer

Room tone is the sound of your recording space with nobody speaking. Audiobooks use it at the start and end of every file and to fill gaps, so the background never drops to dead silence. ACX recommends 1 to 5 seconds at each end of every file, no gap over 5 seconds, and a noise floor of −60 dB RMS or lower.¹ Record 30 to 60 seconds of it each session.⁷

At each end of a file (ACX): 1–5 s
Longest gap (ACX): 5 s
Noise floor, finished: ≤ −60 dB
Record per session: 30–60 s

What room tone is

Film sound calls it “presence”: the “silence” recorded in a space when no one is speaking. It is different from ambience because it has no distinct background sounds, and each room has its own, set by the space and where the microphone sits.² FilmSound.org calls it a location’s “aural fingerprint”, recorded so it can be cut in with the dialogue and keep the background continuous.³

In an audiobook, the room tone is the faint, steady sound under the narration: the room, the air, and the hiss of the microphone and preamp. You don’t notice it while it’s there. You notice when it disappears.

Why audiobooks need it

Edits. When you cut a breath, a mistake or a noise, the gap has to be filled with something. Filled with digital silence, the soundtrack “goes dead”, which listeners hear not as silence but as something failing.² Filled with room tone, the cut is inaudible.
Chapter starts and ends. ACX recommends room tone at the beginning and end of every file, so chapters begin and end naturally.¹
Consistency. ACX wants an audiobook consistent in “audio levels, tone, noise level, spacing”.¹ Even room tone across every file is part of that.
Noise reduction. Tools such as Audacity’s noise reduction learn what to remove from a sample of your room tone.⁶

How long: ACX’s rule

ACX’s current requirements say: “We recommend between 1 and 5 seconds of room tone at the beginning and end of each file for an ideal listening experience. Room tone spacing must not exceed 5 seconds.”¹

One chapter file: room tone, then the narration, then room tone.ACX audio submission requirements, checked 22 October 2026.

How loud room tone can be

Room tone is exactly what ACX’s noise floor requirement measures: “Each file must have a noise floor no higher than −60dB RMS.”¹ Audacity’s audiobook guide suggests that if the noise is quieter than about −65 dB, you may be done, and warns that raising the loudness raises the noise with it.⁵

Where room tone (the noise floor) sits against the voice.ACX thresholds. Your room tone has to stay in the green on the bottom row after mastering.

Noise Floor MeterMeasure your room’s noise floor live with your own microphone, and see how much headroom you’ll have after mastering. Free · runs in your browser · nothing uploadedMeasure my room

How to record room tone

Set up exactly as you’ll record
Same room, microphone, distance, gain and settings, with everything that will be on during the session switched on.
Press record and stay still
Don’t move, breathe quietly away from the mic, and let 30 to 60 seconds go by. Film sound crews record longer when the background changes.
Label it
Name the take “room tone” with the date. Record a fresh one each session and whenever something changes: a new day, a heater on, a mic moved.
Check how quiet it is
Measure it. ACX needs −60 dB RMS or lower in the finished files, and the level you raise the voice by in mastering raises the room tone too.

Audacity’s guide has blunt advice for noisy rooms: there are no tools that remove noise that keeps changing, so traffic, barking dogs or a neighbour’s TV “are now your permanent performance partners.”⁵ Fix the room first; room tone can only be as clean as the room.

How to use it when editing

Fill every cut. Paste room tone over removed breaths, clicks and mistakes instead of deleting to silence. ACX’s audio scientist suggests using your editor’s paste or fill feature to place it quickly.⁴
Even out pauses. Keep gaps natural, and never longer than 5 seconds.¹
Pad the ends. Give every chapter 1 to 5 seconds at the start and end.¹
Use the same session’s tone. Tone from another day can sound different, and the switch is audible.

Room Tone ToolDrop a recording to find its quietest stretch of room tone and loop it seamlessly to any length, ready to paste into gaps. Free · runs in your browser · nothing uploadedMake room tone ACX MasteringMaster chapters to ACX levels; missing room tone at the start and end is added from the file’s own quietest half-second. Free · runs in your browser · nothing uploadedOpen the tool

Room tone, silence and ambience

Room tone compared with silence and ambience
	Room tone	Digital silence	Ambience
What it is	The room with nobody speaking	Zero signal	Background with distinct sounds
Sounds like	Nothing in particular	The audio cutting out	A place: a café, a street
Use in audiobooks	Yes	No	Rarely, as a sound effect

Room tone compared with silence and ambience. Definitions from film sound practice.

Everything else, answered.

What is room tone?

The sound of a space with nobody speaking: the air, the hum of the room and the faint hiss of the microphone and preamp. Every recording space has its own, and recordings sound unnatural when it suddenly drops out.

How long should room tone be in an audiobook?

ACX recommends 1 to 5 seconds at the beginning and end of every file, and says gaps of room tone must not exceed 5 seconds. Older ACX wording, still quoted widely, said 0.5 to 1 second at the start.

How much room tone should I record?

ACX gives no figure. Film sound practice is 30 to 60 seconds for a steady background, and longer if it changes. Recording that much at the start of each session gives you plenty to fill gaps with.

How quiet should room tone be?

At or below −60 dB RMS in the finished file, because room tone is what ACX’s noise floor measurement reads. Aim lower before mastering, around −65 dB or quieter, since raising the voice level raises the noise too.

Can I use silence instead of room tone?

Avoid it. Pure digital silence makes the background vanish and return around every gap, which sounds like the audio cutting out. ACX asks for room tone and a consistent noise level across the book.

Is room tone the same as ambience?

No. Ambience is background with recognisable sounds, such as birds or traffic, used to set a scene. Room tone is the plain sound of the room, without distinct noises.

Can I reuse room tone from another day?

Only if nothing changed. Room tone depends on the room, the microphone position and the settings, so a different day can sound different. Record fresh room tone each session to be safe.

What is room tone used for besides the start and end of files?

Filling gaps where you’ve cut out a breath, a mistake or a noise; keeping pauses even; and giving noise reduction a sample of the noise to remove.

Can I make room tone longer without recording more?

Yes. Our room tone tool finds the quietest stretch in your recording and loops it seamlessly (forwards, then backwards, so the joins don’t click) to any length.