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The model has been in use since 1987 and has proven its basic reliability.
The most important output values of NMR are the masking flag rate, giving the percentage of frames with
audible distortions, as well as the total and mean NMR which are different ways of averaging the distance
between the error energy and the masked threshold.
ODG
According to the ITU-R recommendation BS.1387, the ODG (Objective Difference Grade) is the output
variable from the objective measurement method and corresponds to the SDG (Subjective Difference
Grade) in the subjective domain. The resolution of the ODG is limited to one decimal. One should
however be cautious and not generally expect that a difference between any pair of ODGs of a tenth of a
grade is significant. The same remark is valid when looking at results from a subjective listening test.
Offline measurements
Measurement procedure which does not interact with the ongoing programme transmission.
Online measurements
Measurement procedure which relies on the ongoing programme transmission, or parts thereof.
Origin
The near end of a telephone call. This is usually the party which initiates a call, i.e. the party that dials. In
older versions of OPERA this was the "Caller".
PBX
Private Branch Exchange
PCM
Pulse Code Modulation
Pulse Code Modulation. According to standard ITU-T G.711. Bit rate of 64 kbit/s
PDD
Post Dial Delay
Refers to the time elapsed between the last dial tone and the first response of the network.
PDF
the Probability Density Function of a vector, shows the probability for the occurrence of each individual
number in the vector.
PEAQ
Perceptual Evaluation of Audio Quality
Stands for \Perceptual Evaluation of Audio Quality\", the perceptual measurement technique
recommended for wide band (music) audio signals as ITU-R BS.1387 in 1999. See also www.peaq.org."
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