Alignment Level - The Reason For Alignment Level

The Reason For Alignment Level

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 compression as late as possible.

The problem of loudness wars, which have caused a general fall in audio quality, initially on radio stations, but more recently on CDs too, is well known. As radio stations competed for attention and raise the listener scores their ad revenue is based on, they used audio compression to give their sound more impact. They used level compressors, and in particular multi-band compressors such as optimod that compress different parts of the frequency independently. Such compressors usually incorporate fast acting limiters to eliminate brief peaks, since brief peaks, though they may not contribute much to perceived loudness, limit the modulation level that can be applied to FM transmissions in particular, if serious clipping and distortion are to be avoided. Digital broadcasting has changed all this, since stations are no longer found by tuning across the band, so the loudest ones no longer stand out. Low noise level is also guaranteed regardless of signal level, so that it is no longer necessary to fully modulate to ensure acceptable clarity in poor reception areas. Many professionals feel that the more widespread adoption and understanding of alignment level throughout the audio industry could help bring modulation levels down, leaving headroom to cope with brief peaks, and using a different form of level compression that reduces dynamic range on programmes where this is considered desirable, but does not remove the brief peaks which add 'sparkle' and contribute to clearer sound. CDs in particular have suffered a loss of quality since they were introduced through the widespread use of fast limiting, which, given their very low noise level is quite unnecessary.

Digital audio players such as the iPod, demonstrate the need for a common alignment level convincingly. While tracks taken from recent CDs sound loud enough, many older recordings (such as Pink Floyd albums which notably allowed lots of headroom for stunning dynamic range and rarely reach peak digital level) are far too quiet, even at full volume setting. Older audio systems incorporated typically 12dB of 'overvolume', meaning that it was possible to turn up the loudness on a quiet recording to make maximum use of amplifier output even if peak level was never reached on the recording. Modern devices, however, tend to produce maximum output at full volume only on recordings that reach full-scale digital level. If extra gain is added, then playing a modern CD after listening to a well recorded older one is likely to deafen, requiring the volume control to be turned down by a huge amount. Again, the adoption of a common alignment level (early CDs allowed around 18dB of headroom by common consent) would make sense, improving quality and usability and ending the loudness war.