{{Unreferenced, date=November 2009 Programme level refers to the

signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...

level that an

audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound *Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum * Digital audio, representation of soun ...

source is transmitted or recorded at, and is important in audio if listeners of

Compact Disc The compact disc (CD) is a digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then released in Octo ...

s (CDs),

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transm ...

and

television Television, sometimes shortened to TV, is a telecommunication Media (communication), medium for transmitting moving images and sound. The term can refer to a television set, or the medium of Transmission (telecommunications), television tra ...

are to get the best experience, without excessive

noise Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference aris ...

in quiet periods or distortion of loud sounds. Programme level is often measured using a peak programme meter or a

VU meter A volume unit (VU) meter or standard volume indicator (SVI) is a device displaying a representation of the signal level in audio equipment. The original design was proposed in the 1940 IRE paper, ''A New Standard Volume Indicator and Reference ...

. The level of an audio signal is among the most basic of measurements, and yet widespread misunderstanding and disagreement about programme levels has become arguably the greatest single obstacle to high quality

sound reproduction Sound recording and reproduction is the electrical, mechanical, electronic, or digital inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recordin ...

How it works

Live sound covers an enormous range of levels, but this is not something that can be demonstrated with a conventional

sound level meter A sound level meter (also called sound pressure level meter (SPL)) is used for acoustic measurements. It is commonly a hand-held instrument with a microphone. The best type of microphone for sound level meters is the condenser microphone, whic ...

. Sound level meters respond quite slowly, even on a "fast" setting: they use a

root mean square In mathematics and its applications, the root mean square of a set of numbers x_i (abbreviated as RMS, or rms and denoted in formulas as either x_\mathrm or \mathrm_x) is defined as the square root of the mean square (the arithmetic mean of th ...

(RMS) rectifier which by definition must take a slow running average of the square of the input voltage. Music is complex, and constantly varying, with brief peaks originating from many sources including the initial impact of sticks on cymbals and drums. A loud band might measure 100

dB SPL Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, and in water with a hydrophon ...

on a sound level meter, yet have peaks reaching 130 dB SPL or higher. A recording system must handle these peaks; they can be measured using a peak responding meter with an integration time of 0.5 ms or less (not a standard IEC type PPM which has a longer integration time). The

is useless for properly assessing noise levels, since the commonly used

A-weighting A-weighting is the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level. A-weighting is applied to instrument-measured ...

is based on equal-loudness contours for pure tones, and is not valid for the random noise. The subjective

loudness In acoustics, loudness is the subjective perception of sound pressure. 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". The relation of phys ...

of noise is best measured using a noise-meter to the

ITU-R 468 noise weighting ITU-R 468 (originally defined in CCIR recommendation 468-4, therefore formerly also known as CCIR weighting; sometimes referred to as CCIR-1k) is a standard relating to noise measurement, widely used when measuring noise in audio systems. The ...

standard. The chart below shows, on this basis, the real range of live music, and then the level capabilities of various stages in the audio chain, from

microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and pub ...

loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or ...

Analysing programme levels

This chart is based on the assumption that what goes in should come out—true high-fidelity—and so an

Alignment Level The alignment level in an audio signal chain or on an audio recording is a defined anchor point that represents a reasonable or typical level. It does not represent a particular sound level or signal level or digital representation, but it can ...

(AL) corresponding to 100 dB SPL has been assumed throughout. Any lower level would imply severe clipping at the first stage; the master recording. Top quality

s do not present a problem; most will handle 130 dB SPL without severe

distortion In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio s ...

, and a few manage more than 140 dB SPL. The

master recording Mastering, a form of audio post production, is the process of preparing and transferring recorded audio from a source containing the final mix to a data storage device (the master), the source from which all copies will be produced (via met ...

process, using current 24-bit techniques, offers around 99 dB of "true" dynamic range (based on the ''ITU-R 468 noise weighting'' standard); identical to the dynamic range of a good studio microphone, though very few recordings will use just one microphone, and so the noise on most recordings is likely to be the sum of several microphones after mixing, and probably at least 6 dB worse than shown.

External links

EBU Recommendation R68-2000AES Preprint 4828 - Levels in Digital Audio Broadcasting by Neil Gilchrist (not free)EBU Recommendation R117-2006
(against

loudness war The loudness war (or loudness race) is a trend of increasing audio levels in recorded music, which reduces audio fidelity and—according to many critics—listener enjoyment. Increasing loudness was first reported as early as the 1940s, with ...

)
AES Convention Paper 5538 On Levelling and Loudness Problems at Broadcast StudiosEBU R89-1997 on CD-R levels
Audio engineering Broadcast engineering Sound production technology Sound recording Sound

How it works

Analysing programme levels

See also

External links