Last month we began looking at metering, looking primarily at metering the levels of analog audio. The methods of metering began to change with the advent of digital audio.
We mentioned the RMS meter, which measures the average or effective value of a signal. As we stated last month, the human ear does not hear all frequencies of sound at the same level. So an RMS meter does not indicate volume, only a rough approximation of volume.
So they came up with A-weighting, a method for measuring sound using an equalization curve with a response that simulates that of human hearing. It is based on the equal-loudness curves developed by by Fletcher and Munson. These are plots of sound levels at various frequencies that an average listener perceives as being the same loudness. Meters using A-weighting usually designate levels in dBA.
There is also a B-weighting, C-weighting, and D-weighting, which use different parts of the equal-loudness curves. Most meters will use A-weighting and occasionally B-weighting, while C and D versions are for special situations.
This was pretty the state of metering until 2012. That is when the CALM Act went into effect.
Have you ever quietly been watching a movie on television late at night. Then a commercial came on that was so loud that it startled you and maybe even awakened your spouse or significant other who was asleep in the bedroom next door? Besides irritating you and making you jump for the remote to turn the volume down, it may have cause you to contact your congressman. Well, you're not alone. The FCC and Congress received so many complaints that Congress finally did something and passed Commercial Advertisement Loudness Mitigation (CALM) Act which ordered the FCC to make rules that required commercials to have the same average volume as the programs they accompany. As usual the devil is in the details.
Although you probably felt like the TV stations were deliberately raising the volume of ads to get your attention, the broadcaster say otherwise. The problem was that they were using peak metering to set levels. So a movie had its sound level set for the peak, that one big, loud explosion at the end of the movie. However, the commercial, which was mostly dialog, had no real peak. The result was that the dialog of the movie was several decibels lower than the dialog of the ad.
Because other countries passed similar regulations, the International Telecommunications Union (ITU) came up with a new standard, ITU-R BS.1770, to control loudness in the broadcast industry. Although the exact implementation varies from country to country, this standard specifies the use of K-weighting for metering loudness along with the simultaneous use of peak metering.
K-weighting is a somewhat simplified version of A-weighting. They also came up with new loudness units for measuring loudness, which use K-weighting, LUFS, which stands for Loudness Unit Full Scale. This is term used in Europe, but in the US, they used LKFS, which is Loudness, K-weighted, Full Scale. Although originally the two units were somewhat different, they are now essentially the same.
Loudness meters were introduced that use the new units. Loudness meters measure (a) loudness range, (b) integrated loudness (program loudness), and (c) sliding loudness (short-term). There is also an EBU Mode meter, which measures all those plus momentary loudness.
Loudness range is the difference between the loudest and softest levels in an audio program, an indication of the perceived dynamic range of the program. Integrated loudness (I) is the average loudness as measured for the duration of an entire audio track or program. Sliding loudness (S) is measured over a continuously updated three-minute window. Also called short-term loudness, it is used for moment-to-moment adjustments. Momentary loudness (M) is measured over a 400-ms period and is used for making initial settings of loudness.
Although the loudness meters were developed in response to the needs of the broadcast industry, they are also being implemented into recording situations. They are very helpful in keeping all the tracks of a compact disc sounding similar in loudness.
• On March 31, 1949, RCA released "Texarkana Baby" by country singer Eddy Arnold, the first 45-rpm record to be issued in the US.
• Returning from a trip to Europe in 1956, Mike Stoller was aboard the luxury ship SS Andrea Doria, when it was rammed and sunk by the Swedish liner MS Stockholm off Nantucket Island. When he returned to New York on a rescue freighter, he was greeted by his song-writing partner Jerry Leiber, who told him that "Hound Dog" had just become a hit for "some white kid called Elvis Presley." Stoller replied "Elvis who?" Leiber & Stoller went on to write many more hits for Elvis.
• Dewey Bunnell, Dan Peek, and Gerry Beckley formed the band called America in 1970. Ironically, the trio first met as sons of US Air Force personnel stationed in London.