From Wikipedia, the free encyclopedia Headroom (audio signal processing)
Headroom (audio signal processing)
In digital and analog audio, headroom is the amount by Alignment level is an ’anchor’ point, 9 db below the nom-
which the signal-handling capabilities of an audio system inal level,[citation needed] a reference level which exists
exceed a designated level known as Permitted Maximum throughout the system or broadcast chain, though it may
Level (PML). Headroom can be thought of as a safety zone have different actual voltage levels at different points in
allowing transient audio peaks to exceed the PML with- the analog chain. Typically, nominal (not alignment) lev-
out exceeding the signal capabilities of an audio system el is 0 dB, corresponding to an analog sine wave voltage
(digital clipping, for example). Various standards bodies of RMS voltage of 1.23 volts (+4 dBu or 3.47 volts peak to
recommend various levels as Permitted Maximum Level. peak). In the digital realm, alignment level is −18 dBFS.
• AL = analog level
Headroom in digital audio • SPL = sound pressure level
In digital audio, headroom is defined as the amount by
which digital full scale (FS) exceeds the permitted max-
See also
imum level (PML) in dB (decibels). The European Broad- • Audio quality measurement
casting Union (EBU) specifies a PML of 9 dB below 0 dBFS • Noise measurement
(-9 dBFS), thus giving 9 dB of headroom. An alternative • Programme levels
EBU recommendation allows 24 dB of headroom, which • Rumble measurement
might be used for 24-bit master recordings where it is • ITU-R 468 noise weighting
useful to allow more room for unexpected peaks during • A-weighting
live recording. • Weighting filter
Failure to provide adequate headroom can bring • Equal-loudness contour
about clipping of brief, higher-level transients. • Fletcher-Munson curves
• Loudness war
Headroom in analog audio
In analog audio, headroom can mean low-level signal ca-
External links
pabilities as well as the amount of extra power reserve • EBU Recommendation R68-2000
available within the power amplifiers that drive the loud- • AES Preprint 4828 - Levels in Digital Audio
speakers. Broadcasting by Neil Gilchrist (not free)
• EBU Recommendation R117-2006 (against loudness
Alignment level war)
• AES Convention Paper 5538 On Levelling and
Main article: Alignment level Loudness Problems at Broadcast Studios
• EBU Tech 3282-E on EBU RDAT Tape Levels
• AES17-1998 (r2004): AES standard method for digital
audio engineering -- Measurement of digital audio
equipment
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From Wikipedia, the free encyclopedia Headroom (audio signal processing)
Categories:
• Audio engineering
• Broadcast engineering
• Sound production technology
• Sound recording
• Sound
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