Lindos Articles

Programme Levels & Headroom

Alignment Level

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The '''Alignment level''' in an audio signal chain or on an audio recording is an anchor point that represents a reasonable or typical level. It does not represent a particular sound level or signal level or digital representation, but it can be defined as corresponding to particular levels in each of these domains.

For example, alignment level is commonly 0dBu in broadcast chains in places where the signal exists as analogue voltage. It most commonly is at -18dB FS (18dB below full scale digital) on digital recordings for programme exchange, in accordance with European Broadcasting Union (EBU) recommendations. 24-bit original or master recordings commonly have alignment level at -24dB FS in order 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 9dB of headroom as recommended by the EBU.

Using alignment level rather than maximum permitted level as the reference point allows more sensible headroom management throughout the audio chain, so that quality is only sacrificed through level compression as late as possible.

The more widespread adoption and understanding of alignment level throughout the audio industry could help to solve the loudness war that currently rages. CD's in particular have suffered a loss of quality since they were introduced through the widespread use of level compression, which given their very low noise level is quite unecessary. The incorporation of (switchable) level compression in domestic music systems and car in-car systems would allow higher quality on systems capable of wide dynamic range and in situations that allowed realistic reproduction. Such compression systems have been suggested and tried from time to time, but are not in widespread use - a 'chicken and egg' problem since producers feel they must make programmes and recordings that sound good in car with high ambient noise or on cheap low-power music systems.

Useful Links:

EBU Recommendation R68-2000

Lindos articles - Programme levels

AES Preprint 4828 - Levels in Digital Audio Broadcasting by Neil Gilchrist (not free)

EBU Recommendation R117-2006 (against the loudness war)

AES Convention Paper 5538 On Levelling and Loudness Problems at Broadcast Studios

EBU Tech 3282-E on EBU RDAT Tape Levels

EBU R89-1997 on CD-R levels

Distortion to the People - TC Electronics


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