Los Senderos Studio
Metering, Part 1
 Issue 89 February 2017 

Words from the Glossary

This month we take a look at metering.

This month's terms: meter, VU meter, volume unit, volume, loudness, peak meter, peak program meter, RMS meter. (Note: Click on the term to view its definition in the glossary.)

Metering, Part 1

Recording without metering is like taking a trip without a road map (or nowadays, without GPS). You need to know where you are and where you're going. A meter is an instrument used to measure something. In the recording studio we use them to measure signal levels.

VU Meter
VU Meter

The first meter used for this purpose was the VU meter. For decades they were ubiquitous in recording studios, radio stations, and even on the more expensive tape recorders.

The VU meter was developed in the late 1930s as a joint venture of Bell Laboratories, CBS, and NBC, and was used to measure audio levels that match the response of the human ear, as indicated by the volume unit (vu).

Because the human ear does not hear all frequencies at the same level, simply measuring signal level does not correspond to perceived loudness—what we call “volume.” The VU meter compensated for this by specifying the frequency response and the meter ballistics—how fast and by how much the needle moves for given signal input.

The term volume unit is hardly ever used, only the abbreviation vu, pronounced “vee-you.” (Although the abbreviation is often shown as VU, the correct designation is lower case vu.) In 1939, an attempt was made to standardize the unit by making 0 vu equal to 0 dBm for a pure 1000-Hz sine wave, but it didn't stick. Instead several manufacturers and various industries came up with their own quasi-standards. Most commonly 0 VU represents +4 dBu, but -10 dBV is sometimes used. In the broadcast industry, line level is considered to be +8 dBu, so they set their VU meters to that value.

Peak Program Meter
Peak Program Meter

Despite these differences, the VU meter was quite effective. You set your recording level by allowing the needle to jump slightly into the red (positive vu). While this may seem counter-intuitive, it worked because during that era, all equipment used vacuum tubes. One of the characteristics of vacuum tubes is that as you approach saturation (the point beyond which it can no longer properly handle the signal), the signal becomes nonlinear. In other words, an increasing input signal no longer produces a proportional increase in output. In a sense it was automatically compressing the signal. So going into red was alright as long as you didn't peg the meter.

This all changed when digital audio came into use. Unlike an analog signal which tended to sound warmer as you approached saturation, when a digital signal went into the red, you were clipping—chopping off the tops of the sound wave. And that sounds awful.

Segmented Meter
Segmented Meter

So a new type of meter came into use, the PPM—the peak program meter. Actually, the VU meter was never used much in Europe, where peak meters were generally preferred. These meters were originally mechanical meters just like the VU meters, but with the advent of digital audio, they were generally replaced by segmented meters.

The segmented meter consists of a series of horizontal or vertical LEDs that indicate a level by progressively lighting more LEDs as the audio level increases. In DAWs, a graphical representation of the LEDs is used. They are usually color-coded beginning with green for lower levels, increasing to yellow, and then the dreaded red.

Because a peak meter only measures peaks, the highest instantaneous value of a signal, it is good at detecting clipping, but is not so good indicating volume. For that reason, an RMS meter is sometimes used. RMS stands for root mean square, a method of computing an average or effective value of a signal. Sometimes peak meters and RMS meters are used together—one to prevent clipping and the other to indicate volume. If you look closely at the illustration of the segmented meter, you will see that it indicates both peak and RMS.

However, RMS is not the real answer. An average level is still not volume, because, as we mentioned above, the human ear does not hear all frequencies of sound at the same level.

So next month we will discuss the solution to this problem when we cover Metering, Part 2.

RCA Victor introduced the first 45-rpm phonograph in 1949. At first, all 45-rpm records were produced in color-coded vinyl by genre. Popular music was black, classical was red, popular classical was midnight blue, country was green, R&B was cerise, children's music was yellow, and international music was sky blue. Cerise? That's a deep red color.

Antoine Domino received the nickname “Fats” because he was 5-foot-2-inches tall and weighed 225 lb.

John Fogerty of Credence Clearwater Revival kept a notebook in which he made notes about words and names that would make good song titles. “Proud Mary” was on the list. When he started to write the song, it was about a washerwoman named Mary. However, the first chords he used reminded him of a paddle-wheel boat. So Proud Mary became a boat with the line “rollin' on the river,” which came from a Will Rogers movie.

Spring Concert Series Announced

Following its successful first year, the Blanco Arts in the Park committee has announced the Spring Concert Series for 2017. Unlike last year, when the concerts were on successive weekends, the new series will be spread out over several months.

The dates for the spring concerts will be March 25, April 21, May 5, and May 12, all being presented in Bindseil Park, weather permitting. On May 6, Arts in the Park will hold another art walk with live music on the courthouse lawn.

More details will be provided in next month's newsletter. Or visit the Arts in the Park Facebook page.

Los Senderos Studio, LLC

A Recording Studio in the Hill Country.

8409 N US Highway 281 ★ Blanco, TX 78606-5024
Phone: 512-565-0446 ★ Email: Larry@LosSenderosStudio.com

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