Nominal level
Encyclopedia
Nominal level is the operating level at which an electronic signal processing
device is designed to operate. The electronic circuit
s that make up such equipment are limited in the maximum signal they can output and the low-level internally-generated electronic noise
they add to the signal. The difference between the internal noise and the maximum output level is the device's dynamic range
. When a signal is chained improperly through many devices, the dynamic range of the signal is reduced. The nominal level is the level that these devices were designed to operate at, for best dynamic range.
In audio, a related measurement, signal-to-noise ratio
, is usually defined as the difference between the nominal level and the noise floor
, leaving the headroom as the difference between nominal and maximum output. It is important to realize that the measured level is a time average
, meaning that the peaks of audio signals regularly exceed the measured average level. The headroom measurement defines how far the peak levels can stray from the nominal measured level before clipping
. The difference between the peaks and the average for a given signal is the crest factor
.
There is some confusion over the use of the term "nominal
", which is often used incorrectly to mean "average or typical". The relevant definition in this case is "as per design"; gain
is applied to make the average signal level correspond to the designed, or nominal, level.
s are designed to represent the perceived loudness
of a passage of music, measuring in volume units. The product is designed so that the best signal quality is obtained when the meter rarely goes above nominal. The markings are often in dB
instead of "VU", and the reference level is defined in the product's manual. In professional recording and sound reinforcement gear, the nominal level is 0 VU = +4 dBu
. In consumer level equipment, the nominal level varies, but some standardize to 0 VU = −10 dBV. The difference between consumer and pro equipment revolves around the cost required to create larger power supplies and output higher levels; consumer levels can be generated by battery
-powered gear, but pro levels require power supplies that plug into the mains
.
In broadcasting
equipment, this is termed the Maximum Permitted Level, which is defined by European Broadcasting Union
standards. These devices use peak programme meter
s instead of VU meters, which gives the reading a different meaning.
"Mic
level" is sometimes defined as −60 dBV, though levels from microphones vary widely.
In video
systems, nominal levels are 1 VP-P for synched systems, such as baseband composite video
, and 0.7 VP-P for systems without sync. Note that these levels are measured peak-to-peak, while audio levels are time averages.
Signal processing
Signal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time...
device is designed to operate. The electronic circuit
Electronic circuit
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...
s that make up such equipment are limited in the maximum signal they can output and the low-level internally-generated electronic noise
Electronic noise
Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...
they add to the signal. The difference between the internal noise and the maximum output level is the device's dynamic range
Dynamic range
Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity, such as in sound and light. It is measured as a ratio, or as a base-10 or base-2 logarithmic value.-Dynamic range and human perception:The human senses of sight and...
. When a signal is chained improperly through many devices, the dynamic range of the signal is reduced. The nominal level is the level that these devices were designed to operate at, for best dynamic range.
In audio, a related measurement, signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
, is usually defined as the difference between the nominal level and the noise floor
Noise floor
In signal theory, the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system, where the noise is defined as any signal other than the one being monitored....
, leaving the headroom as the difference between nominal and maximum output. It is important to realize that the measured level is a time average
Average
In mathematics, an average, or central tendency of a data set is a measure of the "middle" value of the data set. Average is one form of central tendency. Not all central tendencies should be considered definitions of average....
, meaning that the peaks of audio signals regularly exceed the measured average level. The headroom measurement defines how far the peak levels can stray from the nominal measured level before clipping
Clipping (audio)
Clipping is a form of waveform distortion that occurs when an amplifier is overdriven and attempts to deliver an output voltage or current beyond its maximum capability...
. The difference between the peaks and the average for a given signal is the crest factor
Crest factor
The crest factor or peak-to-average ratio or peak-to-average power ratio is a measurement of a waveform, calculated from the peak amplitude of the waveform divided by the RMS value of the waveform.C =...
.
There is some confusion over the use of the term "nominal
Real versus nominal value
In economics, nominal value refers to a value expressed in money terms in a given year or series of years. By contrast, real value adjusts nominal value to remove effects of price changes over time...
", which is often used incorrectly to mean "average or typical". The relevant definition in this case is "as per design"; gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
is applied to make the average signal level correspond to the designed, or nominal, level.
Standards
VU meterVU meter
A VU meter is often included in audio equipment to display a signal level in Volume Units; the device is sometimes also called volume indicator ....
s are designed to represent the perceived loudness
Loudness
Loudness is the quality of a sound that is primarily a psychological correlate of physical strength . More formally, it is defined as "that attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud."Loudness, a subjective measure, is often...
of a passage of music, measuring in volume units. The product is designed so that the best signal quality is obtained when the meter rarely goes above nominal. The markings are often in dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
instead of "VU", and the reference level is defined in the product's manual. In professional recording and sound reinforcement gear, the nominal level is 0 VU = +4 dBu
DBU
DBU may refer to:* Dansk Boldspil-Union, in English known as the Danish Football Association* dBu, a decibel measurement of voltage* 1,8-Diazabicyclo[5.4.0]undec-7-ene...
. In consumer level equipment, the nominal level varies, but some standardize to 0 VU = −10 dBV. The difference between consumer and pro equipment revolves around the cost required to create larger power supplies and output higher levels; consumer levels can be generated by battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
-powered gear, but pro levels require power supplies that plug into the mains
Mains electricity
Mains is the general-purpose alternating current electric power supply. In the US, electric power is referred to by several names including household power, household electricity, powerline, domestic power, wall power, line power, AC power, city power, street power, and grid power...
.
In broadcasting
Broadcasting
Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
equipment, this is termed the Maximum Permitted Level, which is defined by European Broadcasting Union
European Broadcasting Union
The European Broadcasting Union is a confederation of 74 broadcasting organisations from 56 countries, and 49 associate broadcasters from a further 25...
standards. These devices use peak programme meter
Peak programme meter
A peak programme meter is an instrument used in professional audio for indicating the level of an audio signal.There are many different kinds of PPM. They fall into broad categories:...
s instead of VU meters, which gives the reading a different meaning.
"Mic
Microphone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
level" is sometimes defined as −60 dBV, though levels from microphones vary widely.
In video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
systems, nominal levels are 1 VP-P for synched systems, such as baseband composite video
Composite video
Composite video is the format of an analog television signal before it is combined with a sound signal and modulated onto an RF carrier. In contrast to component video it contains all required video information, including colors in a single line-level signal...
, and 0.7 VP-P for systems without sync. Note that these levels are measured peak-to-peak, while audio levels are time averages.
See also
- Alignment levelAlignment levelThe alignment level in an audio signal chain or on an audio recording is a defined anchor point that represents a reasonable or typical level...
- Programme levels
- Headroom
- Measurement level
- Transmission level pointTransmission level pointIn a telecommunications system, a transmission level point is a test point or interface, i.e. a physical point in an electronic circuit where a test signal may be inserted or measured, and for which the nominal power of the test signal is specified....
External links
- Nominal Level — Sweetwater glossary
- Level Headed — Nominal Level (explained) plus an SV-3700 modification