PEAQ
Encyclopedia
PEAQ is a standardized algorithm for objectively measuring perceived audio quality, developed in 1994-1998 by a joint venture of experts within Task Group 6Q of the International Telecommunication Union (ITU-R
). It was originally released as ITU-R Recommendation BS.1387 in 1998 and last updated in 2001. It utilizes software to simulate perceptual properties of the human ear
and then, integrate multiple model output variables (MOV) into a single metric. PEAQ characterizes the perceived audio quality as subjects would do in a listening test according to ITU-R BS.1116. PEAQ results principally model mean opinion scores (MOS) that cover a scale from 1 (bad) to 5 (excellent).
remove both redundancy and perceptual irrelevancy in the audio signal so that the bit rate required to encode the signal is significantly reduced. They take into account knowledge of human auditory perception and typically achieve a reduced bit rate by ignoring audio information that is not likely to be heard by most listeners. Traditional audio measurements like frequency response based on sinosoidal sweeps, S/N, THD+N do not reflect the audio codec quality. A psychoacoustic model
must be used to predict how the information is masked by louder audio content adjacent in time and frequency.
Since subjective listening test are time-consuming, expensive and impractical for an everyday use, it was beneficial to substitute listening tests with objective, computer-based methods. Steered by the ITU-R Task Group 6Q, a group of leading sound quality experts developed a new objective model for sound quality: PEAQ. These contributors were:
, that describes the effect that a sound produces into another simultaneous sound. Masking depends on the spectral composition
of both masker and masking signal, and on other variations with time. The basic block diagram of a perceptual coding system is shown in the figure.
The input signal is decomposed into subsampled spectral components. For each sample an estimation of the actual masked threshold is derived using rules known from psychoacoustics. This is the perceptual model of the encoding system. The spectral components are quantized and coded keeping the quantization noise below the masked threshold. Finally is formed the bitstream
.
The analysis of the results are based on the Subjective Difference Grade (SDG). It compares the signal under test with the original reference signal.
and filter banks. The other provides a cognitive processing as the human brain does. The next image represents a simple diagram blocks of the relationship between the human audio system and an objective psychoacoustic model.
From the model comparison of the test signal with the (original) reference signal, a number of model output variables MOV
are derived. Each model output variable may measure different psychoacoustic dimensions. In the final stage the MOV values are combined to produce a MOS-like result that copes with subjective quality assessment (SDG).
There are two variations of the model. The Basic version (less processing intensive) was developed to be fast enough for real-time monitoring. The Advanced version is computationally more demanding and may deliver slightly more accurate results.
ITU-R
The ITU Radiocommunication Sector is one of the three sectors of the International Telecommunication Union and is responsible for radio communication....
). It was originally released as ITU-R Recommendation BS.1387 in 1998 and last updated in 2001. It utilizes software to simulate perceptual properties of the human ear
Auditory system
The auditory system is the sensory system for the sense of hearing.- Outer ear :The folds of cartilage surrounding the ear canal are called the pinna...
and then, integrate multiple model output variables (MOV) into a single metric. PEAQ characterizes the perceived audio quality as subjects would do in a listening test according to ITU-R BS.1116. PEAQ results principally model mean opinion scores (MOS) that cover a scale from 1 (bad) to 5 (excellent).
Motivation
The need to conserve bandwidth has led to developments in the compression of the audio data to be transmitted. Various encoding methodsCodec
A codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"...
remove both redundancy and perceptual irrelevancy in the audio signal so that the bit rate required to encode the signal is significantly reduced. They take into account knowledge of human auditory perception and typically achieve a reduced bit rate by ignoring audio information that is not likely to be heard by most listeners. Traditional audio measurements like frequency response based on sinosoidal sweeps, S/N, THD+N do not reflect the audio codec quality. A psychoacoustic model
Psychoacoustics
Psychoacoustics is the scientific study of sound perception. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound...
must be used to predict how the information is masked by louder audio content adjacent in time and frequency.
Since subjective listening test are time-consuming, expensive and impractical for an everyday use, it was beneficial to substitute listening tests with objective, computer-based methods. Steered by the ITU-R Task Group 6Q, a group of leading sound quality experts developed a new objective model for sound quality: PEAQ. These contributors were:
- OPTICOM GmbH, Erlangen, Germany
- the Fraunhofer Institute for Integrated Circuits, IIS-A, Erlangen, Germany
- Deutsche TelekomDeutsche TelekomDeutsche Telekom AG is a telecommunications company headquartered in Bonn, Germany. It is the largest telecommunications company in Europe....
Berkom, Berlin, Germany - the University of Berlin, Berlin, Germany
- the Institut für RundfunktechnikInstitut für RundfunktechnikThe Institut für Rundfunktechnik GmbH is the research centre of the German broadcasters , Austria's broadcaster and the Swiss public broadcaster . It is located in Munich and is responsible for the research and standardisation of broadcasting technology...
, IRT, Munich, Germany - KPN Research, The Hague, Netherlands
- CCETTCentre commun d'études de télévision et télécommunicationsCCETT or Centre commun d'études de télévision et télécommunications was a research centre created in Rennes in 1972 jointly by the Office de Radiodiffusion Télévision Française and Centre National...
, France - Communications Research Centre, CRC, Ottawa, Canada
Principles
In perceptual coding it is fundamental to determine the level of noise that can be introduced into a signal before it becomes audible. Because the human auditory system is highly non-linear, noise levels vary with time and frequency characteristics of the audio signal. Psychoacoustic studies can deliver threshold criteria for various acoustic events and the resulting perceived sounds. The key is maskingAuditory masking
Auditory masking occurs when the perception of one sound is affected by the presence of another sound.- Simultaneous masking :Simultaneous masking is when a sound is made inaudible by a "masker", a noise or unwanted sound of the same duration as the original sound.-Critical bandwidth:If two sounds...
, that describes the effect that a sound produces into another simultaneous sound. Masking depends on the spectral composition
Frequency spectrum
The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain. The frequency spectrum can be generated via a Fourier transform of the signal, and the resulting values are usually presented as amplitude and phase, both plotted versus frequency.Any signal...
of both masker and masking signal, and on other variations with time. The basic block diagram of a perceptual coding system is shown in the figure.
The input signal is decomposed into subsampled spectral components. For each sample an estimation of the actual masked threshold is derived using rules known from psychoacoustics. This is the perceptual model of the encoding system. The spectral components are quantized and coded keeping the quantization noise below the masked threshold. Finally is formed the bitstream
Bitstream
A bitstream or bit stream is a time series of bits.A bytestream is a series of bytes, typically of 8 bits each, and can be regarded as a special case of a bitstream....
.
The analysis of the results are based on the Subjective Difference Grade (SDG). It compares the signal under test with the original reference signal.
Models
The model follows the fundamental properties of the auditory system and it differences stages of physiological and psychoacoustic effects. The first part model the construction of the signal with a Discrete Fourier transformDiscrete Fourier transform
In mathematics, the discrete Fourier transform is a specific kind of discrete transform, used in Fourier analysis. It transforms one function into another, which is called the frequency domain representation, or simply the DFT, of the original function...
and filter banks. The other provides a cognitive processing as the human brain does. The next image represents a simple diagram blocks of the relationship between the human audio system and an objective psychoacoustic model.
From the model comparison of the test signal with the (original) reference signal, a number of model output variables MOV
MOV
MOV may refer to:* MOV , a mnemonic for the copying of data from one location to another in the X86 assembly language* .mov, filename extension for the QuickTime multimedia file format...
are derived. Each model output variable may measure different psychoacoustic dimensions. In the final stage the MOV values are combined to produce a MOS-like result that copes with subjective quality assessment (SDG).
There are two variations of the model. The Basic version (less processing intensive) was developed to be fast enough for real-time monitoring. The Advanced version is computationally more demanding and may deliver slightly more accurate results.
License
The PEAQ technology as recommended by ITU-R Rec. BS.1387 is protected by several patents and is available under license together with the original code for commercial applications according to ITU fair, reasonable and non-discriminatory terms. For educational use, there exists a free cross-platform program called Peaqb which accomplishes the same functions in a limited manner, as it has not been validated with the ITU data. Another unvalidated implementation of the PEAQ basic model for educational use, PQevalAudio, is available from the TSP Lab of McGill University.See also
- Perceptual Evaluation of Speech Quality (PESQ)PESQPESQ, Perceptual Evaluation of Speech Quality, is a family of standards comprising a test methodology for automated assessment of the speech quality as experienced by a user of a telephony system. It is standardised as ITU-T recommendation P.862...
- Perceptual Evaluation of Video Quality (PEVQ)PEVQPEVQ ' is a standardized end-to-end measurement algorithm to score the picture quality of a video presentation by means of a 5-point mean opinion score...
- sound qualitySound qualitySound quality is the quality of the audio output from various electronic devices. Sound quality can be defined as the degree of accuracy with which a device records or emits the original sound waves...
- audio compressionAudio compressionAudio compression may refer to:*Audio compression , a type of lossy compression in which the amount of data in a recorded waveform is reduced for transmission with some loss of quality, used in CD and MP3 encoding, Internet radio, and the like...
- auditory maskingAuditory maskingAuditory masking occurs when the perception of one sound is affected by the presence of another sound.- Simultaneous masking :Simultaneous masking is when a sound is made inaudible by a "masker", a noise or unwanted sound of the same duration as the original sound.-Critical bandwidth:If two sounds...
- psychoacoustic model
External links
- http://www.peaq.org PEAQ official site
- http://www.crc.ca/en/html/aas/home/peaq/peaq PEAQ at the CRC
- http://www.opticom.de/technology/technology.html PEAQ information from OPTICOM
- http://elvera.nue.tu-berlin.de/files/0829Thiede1998.pdf PEAQ - der künftige ITU-Standard zur objektiven Messung der wahrgenommenen Audioqualität
- http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=01613524 IEEE - Estimating Perceptual Audio System Quality Using PEAQ Algorithm
- http://sourceforge.net/projects/peaqb/ Peaqb project
- http://www-mmsp.ece.mcgill.ca/Documents/Software/index.html PQevalAudio - Matlab and C implementation of PEAQ Basic Model.