The alignment level in an audio
signal chain or on an
audio recording
Sound recording and reproduction is the electrical, mechanical, electronic, or digital inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording t ...
is a defined anchor point that represents a reasonable or typical level.
Analogue
In analogue systems, alignment level in
broadcast
Broadcasting is the data distribution, distribution of sound, audio audiovisual content to dispersed audiences via a electronic medium (communication), mass communications medium, typically one using the electromagnetic spectrum (radio waves), ...
chains is commonly 0
dBu (0.775 volts RMS) and in professional audio is commonly ''0 VU'' (4 dBu, 1.228 volts RMS). Under normal situations, the 0 VU reference allows for a
headroom of 18 dB or more above the reference level without significant distortion. This is largely due to the use of slow-responding
VU meter
A volume unit (VU) meter or standard volume indicator (SVI) is a device displaying a representation of the Signal-to-noise ratio, signal level in audio equipment.
The original design was proposed in the 1940 Institute of Radio Engineers, IRE pap ...
s in almost all analogue professional audio equipment, which, by their design and by specification, respond to an average level, not peak levels.
Digital
In digital systems alignment level commonly is at −18
dBFS (18 dB below
digital full scale), in accordance with
EBU recommendations.
Digital equipment must use peak-reading metering systems to avoid severe digital distortion caused by the signal going beyond digital full scale. 24-bit original or master recordings commonly have an alignment level at −24 dBFS to allow extra headroom, which can then be reduced to match the available headroom of the final medium by
audio level compression. FM broadcasts usually have only 9 dB of headroom, as recommended by the EBU, but digital broadcasts, which could operate with 18 dB of headroom, given their low noise floor even in difficult reception areas, currently operate in a state of confusion, with some transmitting at maximum level, while others operate at a much lower level, even though they carry material that has been compressed for compatibility with the lower dynamic range of FM transmissions.
EBU
In EBU documents ''alignment level'' defines −18 dBFS as the level of the ''alignment signal'', a 1 kHz sine tone for analog applications and 997 Hz in digital applications.
Motivation
Using alignment level rather than
maximum permitted level as the reference point allows more sensible headroom management throughout the audio signal chain;
compression happens only where intended.
Loudness wars have resulted in increasing playback loudness.
Loudness normalisation to a fixed alignment level can improve the experience when listening to mixed material.
See also
*
Audio normalization
Audio normalization is the application of a constant amount of gain to an audio recording to bring the amplitude to a target level (the norm). Because the same amount of gain is applied across the entire recording, the signal-to-noise ratio and ...
*
Full scale
*
Nominal level
*
Transmission-level point
External links
EBU Recommendation R128 - Loudness normalisation and permitted maximum level of audio levels (2010)EBU Recommendation R68-2000EBU Recommendation R117-2006(against
loudness war)
AES Convention Paper 5538 On Levelling and Loudness Problems at Broadcast StudiosEBU Tech 3282-E on EBU RDAT Tape Levels
EBU R89-1997 on CD-R levels{dl, fix-attempted=yes, date=May 2023
Distortion to the People — TC ElectronicsEBU Loudness Group
Audio engineering
Broadcast engineering
Sound production technology
Sound recording
Sound