Nominal level is the operating level at which an electronic
signal processing
Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing ''signals'', such as audio signal processing, sound, image processing, images, Scalar potential, potential fields, Seismic tomograph ...
device is designed to operate. The
electronic circuit
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or Conductive trace, traces through which electric current can flow. It is a t ...
s that make up such equipment are limited in the maximum signal they can handle and the low-level internally generated
electronic noise
In electronics, noise is an unwanted disturbance in an electrical signal.
Noise generated by electronic devices varies greatly as it is produced by several different effects.
In particular, noise is inherent in physics and central to thermod ...
they add to the signal. The difference between the internal noise and the maximum level is the device's
dynamic range
Dynamics (from Greek δυναμικός ''dynamikos'' "powerful", from δύναμις ''dynamis'' " power") or dynamic may refer to:
Physics and engineering
* Dynamics (mechanics), the study of forces and their effect on motion
Brands and ent ...
. The nominal level is the level that these devices were designed to operate at, for best dynamic range and adequate
headroom. When a signal is chained with improper
gain staging through many devices,
clipping may occur or the system may operate with reduced dynamic range.
In audio, a related measurement,
signal-to-noise ratio
Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ...
, is usually defined as the difference between the nominal level and the
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 noise is defined as any signal other than the one being monitored.
In radio com ...
, leaving the
headroom as the difference between nominal and maximum output. 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.
Standards
VU meter
A volume unit (VU) meter or standard volume indicator (SVI) is a device displaying a representation of the Signal-to-noise ratio, signal level in audio equipment.
The original design was proposed in the 1940 Institute of Radio Engineers, IRE pap ...
s are designed to represent the perceived
loudness
In acoustics, loudness is the subjectivity, subjective perception of sound pressure. More formally, it is defined as the "attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud". The relat ...
of a passage of music, or other audio content, measuring in
volume units. Devices are 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 should be defined in the device's manual. In most professional
recording and
sound reinforcement
A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers in enclosures all controlled by a mixing console that makes live or pre-recorded sounds louder and may also distribute those sou ...
equipment, the nominal level is . In semi-professional and domestic equipment, the nominal level is usually −10
dBV. This difference is due to the cost required to create larger power supplies and output higher levels.
In
broadcasting
Broadcasting is the data distribution, distribution of sound, audio audiovisual content to dispersed audiences via a electronic medium (communication), mass communications medium, typically one using the electromagnetic spectrum (radio waves), ...
equipment, this is termed the Maximum Permitted Level, which is defined by
European Broadcasting Union
The European Broadcasting Union (EBU; , UER) is an alliance of Public broadcasting, public service media organisations in countries within the European Broadcasting Area (EBA) or who are member states of the Council of Europe, members of the ...
standards. These devices use
peak programme meter
A peak programme meter (PPM) is an instrument used in professional audio that indicates the level of an audio signal.
Different kinds of PPM fall into broad categories:
*True peak programme meter. This shows the peak level of the waveform n ...
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.
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In video
Video is an Electronics, electronic medium for the recording, copying, playback, broadcasting, and display of moving picture, moving image, visual Media (communication), media. Video was first developed for mechanical television systems, whi ...
systems, nominal levels are 1 V P-P for synched systems, such as baseband composite video
Composite video, also known as CVBS (composite video baseband signal or color, video, blanking and sync), is an analog video format that combines image information—such as brightness (luminance), color (chrominance), and synchronization, int ...
, and 0.7 VP-P for systems without sync.
- "The Y signal has a nominal level of 1Vpp and C signal a level of around 0.5V.", "The nominal signal level is 1Vpp on a 75 ohm terminated line." Note that these levels are measured peak-to-peak, while audio levels are time averages.
See also
*
Alignment level
*
Transmission level point
References
External links
Nominal Level— Sweetwater glossary
Signal processing
Sound