Audio Engineering

Metering (1)

The Music Telegraph | Text 2019/07/04 [12:44]
Audio Engineering

Metering (1)

The Music Telegraph| 입력 : 2019/07/04 [12:44]

 

▲ Analog VU meter

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Metering (1)

 

Meters are fundamental components in professional audio production. All the electronic and magnetic devices have limitations that affect their performance. We must have some way of knowing when, or if we are approaching those limits. Meters allow us to get this information.

 

If we are interested in when a signal will send an amp into overload, then we should be using a meter that would tell us that information. A meter with a warning light or bell or something would work. The fact of the matter is that we have only recently begun to use these types of meters. Since the dawn of analog audio (starting with the phone company) we have been using meters that do not give an accurate indication of the instantaneous level of a signal. Rather we have been using meters that have a relatively slow needle motion and miss a great deal of information. 

 

 

Do you VU? 

 

When the phone company began doing its thing, much was known about how people perceive sound and how electronic circuits worked, but there was not much information that connectedthe two. Before they could do much in the way of processing audio they had to have some way of connecting the human experience to the electronic circuits that produced the sounds. To better correlate the two, the phone company developed the decibel system of level measurement and the VU meter. VU stands for "Volume Units" and it pretty much describes what the meter was supposed to do, namely indicate on a scale the sound level as perceived by a listener. 

 

 

You say "twice as loud" I say "ten times as loud".

 

The ear/brain does not know the absolute value of a sound. It only knows that one sound is louder/softer than another. The actual value cannot be known accurately. Also, the ear senses sound level in a non-linear manner. That is, twice as much sound level will not sound like twice as loud. In fact it will be barely noticed as a change at all. It takes ten times more sound power for the ear to sense the increase as twice as much. In mathematics this is called a logarithmic progression. On top of all that, we don't evaluate sound very quickly either. It takes a finite amount of time for the ear to know what a sound is and relay that information to the brain for cognition. This delayed response can be up to a few milliseconds. It is called temporal (time) integration. 

 

The VU meter has a circuit designed take both the logarithmic progression and the temporal integration characteristic into account. The meter will register sound as the ear perceives it (logarithmic calculation of level), and at a rate close to the ear's response time (the rise and fall timefor the needle or led on a VU meter is standardized at 300 ms.). This is good and this is bad.

 

 

 

 

 

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