Wild variations in the levels of program audio has long been a problem for broadcast outlets. Due to controversy over varying audio levels, governments have forced broadcasters to specify specific loudness levels for all programming. In this article, we’ll look at how audio has moved beyond traditional types of level monitoring to a new method.
For many years, most audio producers monitored audio levels with a peak meter — a measuring instrument that indicates the instantaneous level of an audio signal that is passing through it. It measures the peak value of a waveform, rather than its mean value or RMS value.
The problem, however, with all traditional metering is it does not take human perception into account. A VU meter or a peak meter doesn't correspond to how the audio actually sounds to our ears. It’s possible for the audio to be measured one way on meters but sound totally different. On a peak meter, telephone audio often appears hotter than it really sounds, while music can often have the opposite effect.
As a result of the loudness wars of the past decade, there is now a better way to measure the loudness of audio. It is called, appropriately, the loudness meter and is far more useful than traditional meters for audio monitoring. In short, loudness meters are more accurate to show what we are hearing than doing measurements.
Loudness metering was first implemented in European television broadcasting half a decade ago and is the technology behind the FCC's CALM Act in the United States. Now, technology to balance levels from one segment to the next involves virtually all types of media — from broadcasting to streaming services.
Today, there are many options for producers wanting to do loudness metering before it is sent to distribution outlets. Loudness meters are now built into many audio editors. There are also third party plug-ins, from basic low-cost to very sophisticated software.
Loudness is the subjective perception of sound pressure. It is on a scale extending from quiet to loud. In different industries, loudness may have different meanings and different measurement standards. In broadcasting and cinema, ITU-R BS.1770, the International Telecommunications Union (ITU) standard refers to the relative loudness of different segments of electronically reproduced sounds from mono to 5.1 surround. It means “loudness, K-weighted, relative to full scale" (LKFS). The standard was designed to enable normalization of audio levels for delivery of broadcast TV and other video.
Loudness, a subjective measure, is often confused with physical measures of sound strength such as sound pressure, sound pressure level (in decibels), sound intensity or sound power. Filters such as A-weighting and LKFS attempt to compensate measurements to correspond to loudness as perceived by the typical human being.
The sensitivity of the human ear changes as a function of frequency. Humans with normal hearing are most sensitive to sounds around 2–4 kHz, with sensitivity declining to either side of this region. A complete model of the perception of loudness includes the integration of SPL by frequency.
Historically, loudness was measured using an "ear-balance" meter in which the amplitude of a sine wave was adjusted by the user to equal the perceived loudness of the sound being evaluated. Now, the measurement of loudness is based on a summation of energy in critical bands.
Loudness normalization is a specific type of audio normalization that equalizes perceived sound levels. It attempts to insure that commercials do not sound louder than television programs. Loudness normalization software exists for a number of major audio editing applications. Many are compatible with VST, AU and ProTools plug-in formats. Hardware meters are also available with analog and/or digital inputs.
Using the new generation of loudness meters is relatively easy. They display measurements in a unit called Loudness Units Full Scale, or LUFS. Recognize there’s a difference between the unit used on peak meters (dBFS) and LUFS. The unit dBFS (Decibels relative to Full Scale) is solely a measurement of electrical level, without any of the benefits that loudness metering brings.
Settings on these meters is determined by the individual media distribution outlet. It is best for audio producers to use pre-sets for each service. For national distribution of programming, integrated measurement is usually the primary metric to determine compliance with their new loudness standards. In some audio editors, integrated loudness can be accomplished off-line with faster than real time measurement of media files.
Certain audio applications for news reporters makes loudness normalization easy. First, the broadcast organization standard is put into a pre-set. Then “Auto Level” is applied. It allows the user to accomplish normalization either manually or automatically to clips and recordings. Some applications for new reporters apply the loudness standard automatically without any operator intervention.
New loudness tools helps bring consistency to all audio. It balances levels when they widely differ and insures meeting distribution guidelines of various distribution outlets. The old generation of audio metering is history. Use modern loudness technology for more accurate results.
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