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Filmmaking Dictionary: Number 0 / 0 dBFS
Definition
0 dBFS means zero decibels relative to digital full scale. On a conventional fixed-point audio sample-peak meter, it is the top of the scale. Signals that require values beyond the representable range are clipped unless their level is reduced before that limit is reached.
Levels below full scale are shown as negative values, such as −12 dBFS or −20 dBFS. Those negative numbers do not indicate faulty or missing audio. They describe how far the signal is below the reference.
Headroom During Recording
Dialogue changes from take to take. A line delivered quietly in rehearsal may become a shout during the performance, and a small movement toward the microphone can also raise the recorded level. Leaving space below full scale gives those changes somewhere to go.
If a sample peak reads −12 dBFS, it is 12 dB below full scale at that measurement point. That does not prove every earlier stage is clean: a wireless transmitter, microphone or analogue input may already have overloaded before the signal reached the meter.
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0 dBFS Is Not a Dialogue Target
Do not raise ordinary dialogue until it repeatedly touches 0 dBFS. Set recording levels for the actual performance, the recorder and the production workflow. Monitor the signal and preserve enough headroom for the expected peaks.
A reference tone at −20 dBFS or −18 dBFS is an alignment convention, not an instruction to make every spoken word hit that number. Similarly, a programme-loudness requirement in LUFS and a delivery true-peak limit describe different measurements.
Sample Peaks and True Peaks
A sample-peak meter checks the stored sample values. A true-peak meter estimates the peaks of the reconstructed continuous waveform, including peaks that can occur between samples. A signal whose samples remain below full scale can still produce a reconstructed peak above it.
For delivery, use the required true-peak measurement and the destination’s specification. A meter merely staying out of its red area is not a substitute for checking the finished export.
What Changes With 32-Bit Float?
A 32-bit floating-point file can store values above the usual 0 dBFS reference. If the recording chain captured the signal without overload, reducing its level in compatible software can bring those values below full scale without the flat-topped distortion associated with fixed-point clipping.
That storage capability does not make microphones or analogue electronics unlimited. A microphone capsule, transmitter or recorder input can still distort. Turning down a file cannot restore information already lost before or during conversion.
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Practical Checks
- Confirm the recording format: Fixed-point and floating-point workflows handle over-range values differently.
- Check the whole path: Watch input, track and output meters where available.
- Listen: Distortion can occur even when a later meter looks safe.
- Check the export: A floating-point project may still clip when delivered as fixed-point audio or played through an overloaded output.
Frequently Asked Questions
Can a digital file contain levels above 0 dBFS?
A floating-point file can. Conventional fixed-point PCM has a finite full-scale range.
Is 0 dBFS the same as 0 VU?
No. VU uses a nominal alignment reference and different meter behaviour. The relationship depends on calibration.
Related Terms
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