Overview of ARIB Technical Report (TR-B32)
|TR Number||ARIB TR-B32|
|Technical Report Name||Operational Guidelines for Loudness of Digital Television Programs|
This technical report assembles operational guidelines for loudness and technical requirements for the maximum allowable peak level in the digital television broadcasting.
This technical report is applied to the audio signal of all full-packaged programs to be produced, transported, exchanged and played-out in digital television broadcasting. Here, the program refers to a general program or CM.
|A-weighted sound pressure level||
This is the characteristic of the audibility compensation filter used for noise level measurement.
"The noise level" is a measured value with insertion of an A-weighted sound pressure level filter.
Sensitivity of human hearing varies by the frequency (e.g., it is hard to hear the sound of the low frequency) so that it is necessary for noise level measurement to compensate the input signal of a microphone.
The A-weighted sound pressure level filter is used for the compensation.
|B-weighted sound pressure level||This is one of the characteristics of the audibility compensation filter used for noise level measurement. It is not used with the current sound-level meter. It is specified for the noise measurement of medium level.|
This is a unit to express the level of the true peak meter using the peak level measurement algorithm by oversampling specified in Rec. ITU-R BS.1770.
The precision of the measurement of true peak improves along with the increase of a multiple of oversampling, but it is appropriate to use 4 times oversampling considering the complexity of calculation.
This is one of the digital filters.
An output signal is fed back to input by a recursive filter. The reply of the impulse becomes infinite. This is an infinite impulse reply filter.
|K-weighted sound pressure level||
This is the characteristic of the audibility compensation filter specified in Rec. ITU-R BS.1770.
It consists of two pre-filters. The first step is the filter which simulates head sound effects, and the second step is the RLB properties filter. The measurement that is near to human audibility is enabled by using a K-weighted sound pressure level filter.
|LKFS||This is the unit of loudness level which is calculated by loudness measurement algorithm specified in Rec. ITU-R BS.1770.|
|LU||This is the unit of loudness level used in a loudness meter. It expresses a relative value of loudness with 0LU as a target loudness level. The change of 1LU is equal to the change of 1dB.|
|RLB-weighted sound pressure level||
This is the weighting of the second step filter of K-weighted sound pressure level defined in Rec. ITU-R BS.1770.
It is a modified B-weighted sound pressure level, so that it is called modified B-weighted sound pressure level.
This is a meter which measures the volume of an audio signal.
It is designed to replace the audio signal with a unit of volume called Volume Unit so that the meter shows volume level that is near to the feeling of a person.
It shows 99% indication in 0.3 seconds for the response time of the meter for the input signal. There is a problem that it does not show accurate response for the peak signal with rapid increase, but it has been used for many years.
|Oversampling||This is to use sampling frequency of several times of the theoretical sampling frequency, when an analog signal is converted into a digital signal or vice versa.|
|Overlapping||In this technical report, it refers to technique to divide while an adjacent gating block is duplicated each other. The quantity of the overlap is 75% (300ms).|
This is to separate measured values by a certain threshold.
The calculation algorithm of a loudness level in this technical report removes the value that is smaller than the threshold to obtain the loudness level by using absolute gating and relative gating
By doing so, the loudness level which is nearer to subjectivity can be obtained.
In this technical report, an input signal is divided into the block of 400ms length in order to apply gating in loudness calculation.
One of the block of 400ms length is called a gating block.
This is the peak of an encoded digital signal.
The normal peak meter (sample peak meter) displays the maximum of the digital signal in a certain block as a peak level.
This is to reconstitute the sound with more than 3 channels into the sound with 2 (or 1) channels.
Generally, it is used when 5.1ch surround-sound is converted into 2 channels (stereo).
|Target loudness level||This is the average loudness level of a program aiming to keep the hearing quality of the program appropriately.|
|Digital signal||In this technical report, this is the "linear PCM digital signal" unless specified otherwise.|
This is the peak of the analog signal and called "the true peak".
The sample peak meter in general use may not display the true peak that could exist between a sample and a sample.
A peak after oversampling is often called the true peak for convenience. Please mind not to confuse it.
|Normalize||In this technical report, this is to normalize playback sound level of a program by adjusting it to a certain standard level if an average sound level differ a program by a program.|
This is the maximum coded level of a digital signal.
It may be called 0dBFS or Full Scale Digital.
|Head room||This is a margin from a standard level to a clipping level. The head room of a digital signal is from a standard level to a full bit.|
In this technical report, this is the data added in an audio signal, which describes the control information of the signal.
The sound quality can be controlled by adding metadata to an audio signal to be played out.
|Loudness||This is the volume of sound that a person feels (quantity of sense of the sound).|
In this technical report, this is the common name of the calculated value of loudness which is calculated from a digital recording level based on loudness measurement algorithm.
Calculated values with different calculation method including the calculated value without gating processing, the calculated value in the gating block (400ms length), and the calculated value after absolute gating and the relative gating are all called “loudness level” unless otherwise distinguished.
LKFS is used for a unit
This is one of the pulse code modulation.
It has basic process of sampling, quantization, and encoding, but does not employ data compression for encoding.
Generally PCM refers to linear PCM. There are also APCM, ADPCM.
This is to adjust the difference in standard level between equipment and system.
The level set is required for analog recording, when digital signals are converted to analog signals (D/A conversion).
|Audio mode||This is the audio system such as monophonic, stereophonic, 2 sounds, surrounds.|
|Absolute gating||In this technical report, this is a process to remove gating blocks less than absolute threshold -70LKFS to be considered as no sound.|
|Relative gating||In this technical report, this is a process to remove gating blocks with less than the relative threshold, 10dB smaller than loudness level after the absolute gating.|
|Equivalent noise level||
This is the displayed value of noise (fluctuated noise) level fluctuated time to time by averaging total energy of measurement section T in time.
The average energy of measurement section T is obtained by averaging squared sound pressure (spontaneous pressure).
The equivalent noise level is expressed as noise level of the steady noise with average energy, which is equivalent to average energy in fluctuated noise section T.
Officially, the equivalent noise level uses LAeq,T for a quantifier and dB for a unit.
As a custom, LAeq, LAeq and Leq are used for a quantifier, or in some cases only dB(A) and dBA are used to express.
To measure "noise level" including an equivalent noise level, an A-weighting audibility compensation filter is used.
|Average loudness value||
This is the loudness level of any measurement section which is calculated using loudness measurement algorithm including all gating processing described in Chapter 3.
Alternatively, it is called long term loudness or integrated loudness.
"The average loudness level of the program" stands for the average loudness level with a measurement section from the start of the program and the end of it.
2. Amendment History
|Ver.||Amendment or Enactment Date||Amendment summary|
ARIB STD-B59; Three-dimensional Multichannel Stereophonic Sound System for Programme Production was revised in July,2016. To follow above, this technical report is revised to add to weight coefficient for the labels of 7.1 channels, and add to Check Signals for 22.2 channels and 7.1 channels.
Furthermore, this technical report is revised to stipulates the correction value for gain of pre-filter is corresponded with 997Hz sine wave, but not 1kHz sine wave, and to make modifications for the purpose of unification and the clarification of the term.
A conventional measuring method for sounds up to 5.1ch defined in Rec. ITU-R BS.1770-3 is expanded to the measuring method for three-dimensional sounds exceeding 5.1ch defined in revised Rec. BS. 1770-4.
To follow above, this technical report is revised to meet exceeding 5.1 channels.
|1.3||07.03.2015||This is to clarify the measuring method of the average loudness level when a sound mode is monophonic.|
This is to clarify that the purpose of this report is to truly specify the management of the program by the average loudness level and the true peak level.
And a short time measurement mode is beyond the scope of the report.
A meter characteristic and requirements described in Rec. ITU-R BS.1771 is added as information under the positioning of "reference materials."
This technical report specifies the operation based on loudness measurement algorithm specified in Rec. ITU-R BS.1770.
By using a loudness meter based on this specification, the average loudness level of the sound of the whole program is obtained.
And the level is kept uniformity to optimize the sound level difference of the programs.
When the audio level management by loudness is started, a method is required to confirm weather loudness meter is based on the algorithm specified in this report.
This revision is to specify seven kinds of check signals which enable to confirm operation check by measuring them with a loudness meter and compare them with expected values.