Science Meets Arts: An Introduction to Perceptual Audio Coding

EQ2460: Seminars in Wireless Systems

February 22, 2017 KTH, Stockholm

Erik Björkman, M.Sc. EE Research Engineer, ATG Sound Technology Research Dolby Sweden AB www.dolby.com | [email protected] | http://se.linkedin.com/in/ebjorkm What is a Perceptual Audio Codec?

© 2016-17 DOLBY LABORATORIES, INC. 2 What is a Perceptual Audio Codec?

• Meaning • Perceptual ~ related to human perception • Audio ~ from the Latin verb audīre or audiō (“to hear” or “I hear”) • Codec ~ (en)coder + decoder ≈ codec

• Data compression • lossless coding vs. lossy coding

 Sound example • Original (CD-quality) 1411.2 kbps ≈ 1.4 Mbps – 16-bit PCM, 44.1 kHz, stereo – BW = 22.050 kHz • Perceptual audio codec 24 kbps – Compression ratio ~1:59 – BW = 14.815 kHz

© 2016-17 DOLBY LABORATORIES, INC. 3 Presentation Outline

• My Background

• Dolby Laboratories • About Dolby • Overview of recent products • Master’s thesis proposal

• Introduction to Perceptual Audio Coding • Psychoacoustics • Waveform Coding – Sub-Band Coding (SBC) • Parametric Coding Algorithms – Spectral Band Replication (SBR) – Parametric Stereo (PS)

© 2016-17 DOLBY LABORATORIES, INC. 4 My Background

• Started the E programme at KTH 2006

• Non-matriculated graduate student at Stanford University 2009/2010

• Erasmus Mundus research intern at the MTG of UPF in Barcelona 2011

• Consultant in RF and electronics design at Tritech Technology AB 2012-2016

• Master’s degree from KTH completed in 2015

• Research engineer at Dolby Sweden AB since October 2016

Hardware setup for headphone measurements during © 2016-17 DOLBY LABORATORIES, INC. 5 Master’s degree project, Signal Processing Lab, KTH. What’s Dolby to you?

© 2016-17 DOLBY LABORATORIES, INC. Dolby Laboratories

• Founded 1965 by Ray Dolby (1933-2013) • Dolby Noise Reduction [1]

• Technologies for entertainment businesses • Cinema audio and video • Home theaters • Audio and video coding • Audio post-processing • Video and image processing • …and more(!)

• Product concepts • Professional equipment • Technology licensing for consumer products

Ray Dolby was honored with a star on the Hollywood © 2016-17 DOLBY LABORATORIES, INC. 7 Walk of Fame on January 22, 2015, adapted from [2]. Dolby Sweden

• Dolby Laboratories • Headquarters in San Francisco • ~40 offices worldwide • ~2000 employees • ~400 employees in R&D or related

 Dolby Sweden • Coding Technologies – originally founded by Lars “Stockis” Liljeryd in 1997 – Dolby acquired Coding Technologies in 2007 • ~15 researchers • Research focused on audio compression • Office in Vasastan, Stockholm

Fussball table at Dolby Sweden with a Dolby Conference © 2016-17 DOLBY LABORATORIES, INC. 8 Phone [3,4] in the background. Dolby Products

Some of our recent products include

• Dolby Atmos [5,6]

• Dolby Vision [7-9]

• Dolby Cinema [10]

• Dolby Atmos for the Home [11,12]

• Dolby AC-4 [14-19]

• Dolby Home Theater v4 [20]

Feel Every Dimension in Dolby Atmos. © 2016-17 DOLBY LABORATORIES, INC. 9 Dolby Atmos

Dolby Atmos trailer (blank slide in hand-out version). © 2016-17 DOLBY LABORATORIES, INC. 10 Dolby Atmos

• Audio platform for cinema

• Released in 2012

• Novelties • Audio objects • Overhead speakers, front surround speakers • Up to 64 individual speaker feeds

• 650+ movies mixed for Atmos

• ~2700 planned or installed Atmos screens • Closest Atmos screen(s): – Filmstaden Scandinavia #2, #3, #4, Solna [21]

Channel-based vs. object-based surround, adapted © 2016-17 DOLBY LABORATORIES, INC. 11 from [6]. Dolby Atmos: Rendering

• Inputs: up to 128 tracks • 9.1 bed (static) • 118 objects (dynamic)

• Outputs: up to 64 speaker feeds • Filmstaden Scandinavia [21] – Screen #2: 55.1 – Screen #3: 47.1 – Screen #4: 42.1

• Benefits • Increased immersive sound experiences • Reduced singular-sweet-spot effect

Reproduction principle for Dolby Atmos for the Cinema, © 2016-17 DOLBY LABORATORIES, INC. 12 adapted from [6]. Dolby Atmos: Speaker Outline Rfs Rss Rs = Rss + Rrs

• Overhead surround speakers Rrs • Enables sounds or objects from above

• Front surround speakers Lfs / Rfs • Surround speaker arrays (L = Left, R = Right) 5.1: L/R surround Ls / Rs

7.1: L/R side/rear surround Lss / Lrs / Rrs / Rss Lrs 9.1: Two more arrays for surround bed Lfs / Lrs + 7.1 • Increased spatial resolution in the azimuthal plane

• Individual feeds for surround speakers • Previous platforms Lfs Lss Ls = Lss + Lrs – Surround speakers are only grouped as arrays • Object positions – Enables arbitrary spatial rendering

Speaker outline for a Dolby Atmos theater, adapted © 2016-17 DOLBY LABORATORIES, INC. 13 from [6]. Dolby Vision

• Traditional TVs • Legacy: Cathode Ray Tube (CRT) technology • Brightness from 0.117 to 100 nits (1 nit = 1cd/m2) – Sunny day may be measured at up to 50,000 nits

• HDR reproduction • Poor reproduction of HDR images at ≤ 100 nits • Narrow dynamic range

• Modern TVs may offer playback at 300- 500 nits • Image-distorting post-processing depends on manufacturer and model – Lack of source data for post-processing

Brightness of a HDR flower image, adapted from [8]. © 2016-17 DOLBY LABORATORIES, INC. 14 Dolby Vision

• Research at Dolby • 0.001 to 10,000 nits to please 90% of viewers [9]

• Dolby Vision concept • Standardize post-processing – Extract metadata during image pre-processing – Master images with a calibrated display (Pulsar) – Algorithms are tuned to each TV or monitor • No new codec required – Dual layer: base (SDR) + enhancement (EDR; Vision) – SDR images transmitted through industry-standard codecs (HEVC, AVC) – Enhancement layer ignored by SDR displays

Summary of dynamic range subjective test results, © 2016-17 DOLBY LABORATORIES, INC. 15 adapted from [9]. Dolby Vision

• Perceptual Quantizer (PQ) • Novel EOTF allows coding a 10,000-nit range with 12 bits instead of 14 bits • Standardized as SMPTE ST-2084

• Image mastering at 4,000 nits • CMU maps images to a reference display at SDR brightness 100 nits • EDR metadata enables rendering to arbitrary brightness up to 4,000 nits • Up to 10,000 nits in future versions

• More detailed images (EDR = HDR + WGC) • Higher dynamic range (HDR) • Wider color ”gamut” (WCG) • Results in greater contrast and color ”volume”

Graphical representations of gamut and dynamic range, © 2016-17 DOLBY LABORATORIES, INC. 16 adapted from [8]. Dolby Cinema Total cinema experience with Dolby Atmos, Dolby Vision and premium interior design.

Dolby Cinema at AMC, adapted from [10] © 2016-17 DOLBY LABORATORIES, INC. 17 Dolby Atmos for the Home

• Audio reproduction system for the home theater

• Released in 2014

• Immersive content via… • Blu-ray • Streaming • Broadcast

• Speaker options • Traditional surround system + either: – overhead speakers – upward-firing Atmos speakers • Atmos enabled sound bar + optional subwoofer

Dolby Atmos for the Home 7.1.6 surround system with © 2016-17 DOLBY LABORATORIES, INC. 20 upward-firing Atmos speakers, adapted from [23]. Dolby AC-4

• State-of-the-art audio codec • Broadcasting • Streaming

• End-to-end system from content creation to distribution and playback

• Key features • Personalization and accessibility • Support for immersive content • Efficiency: 50 % greater compression efficiency compared to Dolby Digital Plus (DD+) • Video-frame alignment

Audio representation in DD+ (conventional) vs. AC-4 © 2016-17 DOLBY LABORATORIES, INC. 21 (present), adapted from [18]. AC-4 Video-Frame Alignment

Conventional approach

AC-4

AC-4 video-frame alignment, adapted from [18]. © 2016-17 DOLBY LABORATORIES, INC. 22 Complexity Comparison: Enhanced AC-3 (DD+) vs. AC-4

Number of pages used to describe the respective syntax elements of Enhanced AC-3 and AC-4, adapted from [17]. © 2016-17 DOLBY LABORATORIES, INC. 23 Dolby Home Theater v4

Surround Surround Virtualizer Decoder Volume Maximizer Dialog Enhancer Audio Optimizer Intelligent EQ Audio Regulator Volume Leveler Improve Content Quality Graphic

Enhance the Playback the Enhance Playback System EQ

© 2016-17 DOLBY LABORATORIES, INC. 24 Master’s Thesis Proposal: Algorithm for Loudness Metering of Object-Based Audio Content

Location: Dolby Sweden office, Stockholm, Sweden

Duration, Start: 20 weeks (30hp); Flexible (a.s.a.p)

Objective: Develop and evaluate real-time algorithms for loudness-leveling of object-based audio content

Profile: • Last-year MSc EE, MSc CS student or similar with focus on digital signal processing • Courses or practical experience in or more of the following: audio signal processing, psychoacoustics, non-linear signal processing • Good programming skills in C/C++ and experience in Matlab or Python for digital signal processing • Excellent communication skills and fluent in English

Applications: Apply online at https://career4.successfactors.com/career?company=Dolby , requisition number 24981

© 2016-17 DOLBY LABORATORIES, INC. 25 Introduction to Perceptual Audio Coding

Sub-Band Coding & Parametric Coding Algorithms Audio Coding (compression)

• General objective • To reduce the number of bits needed to represent an audio signal in a digital form

• Lossless coding: redundancy reduction • Perfect reconstruction – Comparable to general data compression; “.zip” Perceptual audio coding • Dolby TrueHD, FLAC

 Lossy coding: irrelevancy reduction • “Intelligent” quantization • Reconstructed signals contains additional quantization noise and time-aliasing distortion – Ideally: coding artifacts are inaudible – Comparable to lossy image compression; “.jpeg” • AC-4, Dolby Digital Plus, AAC, mp3, ogg vorbis

© 2016-17 DOLBY LABORATORIES, INC. 27 Perceptual Audio Coding

• Objective • To use as few bits as possible

• Straight-forward solution • Coarser quantization – uses less bits but… – introduces more noise(!) • What’s the possible trade-off then? – No need to reproduce sounds that “we” can’t hear

• Alternative solution • Exploit observed limitations of human hearing – Sub-band coding (waveform data) – Parametric coding algorithms (parametric data)

Outline of a perceptual audio codec (sub-band coding). © 2016-17 DOLBY LABORATORIES, INC. 28 Psychoacoustics

• Is human hearing linear? • Pitch or frequency detection mechanisms

• Absolute threshold of hearing

• Masking phenomena • Spectral or simultaneous masking* – Frequency domain • Temporal or non-simultaneous masking – Time-domain: forward masking, backward masking

• Frequency resolution • Critical bandwidth – Low vs. High frequencies

Absolute threshold of hearing, adapted from [24]. © 2016-17 DOLBY LABORATORIES, INC. 29 Spectral Masking

• Masking thresholds • Spectral components of simultaneous sounds below the masking threshold are inaudible • Frequency-dependent • Level-dependent

• Playback at different levels • Requires compromise and approximation

• *Importance of spectral masking • May be the most important psychoacoustic phenomenon applied in perceptual audio codecs

• EQ2321 Speech and Audio Processing • Launched in P3, 2018 • 7.5 credits

Spectral masking thresholds for critical-band-wide © 2016-17 DOLBY LABORATORIES, INC. 30 noise, adapted from [24]. Quantization Noise

• Signal-to-Quantization-Noise-Ratio • SQNR 20 log 2 dB 6.02 · dB • quantization bits

• CD-quality audio

• 16-bit PCM stereo audio sampled at 44.1 kHz

• SQNR 6.02 · 16 dB 96 dB

• The figure to the right • Q-noise << Masking threshold < Audio signal

• Weak sounds • Q-noise ~ Masking threshold • What happens if played through a powerful amplifier?

Quantization noise spectrum (dark grey) in linearly © 2016-17 DOLBY LABORATORIES, INC. 31 quantized audio, adapted from [25]. Ideal Audio Codec

• Quantization errors just below the masking threshold… • …if the bitrate is sufficiently high

 Sound example • Original (CD-quality) ~1.4 Mbps – BW = 22.050 kHz • AAC (SBC) 128 kbps – BW = 16.0 kHz – Compression ratio ~1:11 • Difference signal @ –19.3 dB • White noise @ –19.3 dB • Original + white noise SNR @ +19.3 dB

Quantization noise spectrum (dark grey) of an ideal © 2016-17 DOLBY LABORATORIES, INC. 32 perceptual audio coder, adapted from [25]. Sub-Band Coding (SBC)

• Compute the masking threshold • Perceptual masking model derived from psychoacoustic experiments

• Encoding • Split the signal into sub-bands • Quantize the signal within each sub-band – Q-error < Masking threshold in each sub-band – Use an “optimal” number of bits in each sub-band

• Decoding • Decode the quantized sub-band signals • Synthesize output waveform in a synthesis filterbank – “Inverse encoding”

Quantization concept in sub-band coding. © 2016-17 DOLBY LABORATORIES, INC. 33 Low-Bitrate Coding

• Bitrate to low • Quantization errors becomes audible

 Sound example • Original (CD-quality) ~1.4 Mbps – BW = 22.050 kHz • AAC (constrained BW = 16.0 kHz) – BW = 16.0 kHz 48 kbps – BW = 16.0 kHz 24 kbps

 Bandlimit the input signal?

Quantization noise spectrum (dark grey) of a © 2016-17 DOLBY LABORATORIES, INC. 34 suboptimal audio coder, adapted from [25]. Band-Limiting

• Less audible quantization errors…

• …but more spectral “distortion”

 Sound example • Original (CD-quality) ~1.4 Mbps – BW = 22.050 kHz • AAC (unconstrained BW) –BW 8.5 kHz 48 kbps – BW 6.6 kHz 24 kbps

 Other remedies? • Parametric coding algorithms…

Quantization noise spectrum (dark grey) of an ideal but © 2016-17 DOLBY LABORATORIES, INC. 35 bandlimited audio coder, adapted from [25]. Parametric Coding Algorithms

Spectral Band Replication & Parametric Stereo Spectral Band Replication (SBR)

• Problem: available bitrate too low

• Idea • Human hearing has relatively poor high-frequency resolution • Correlation between low and high frequenies • “Reconstruct” high-frequency components – Transposition of bandlimited waveform – Adjust transposed frequencies with parameters estimated by the encoder – Reconstruction outline on the next slide…

• Solution: Spectral Band Replication [25] • Developed by Coding Technologies • Used in mp3PRO and aacPlus v1 (HE-AAC) – SBC (mp3 or AAC core) + SBR

• A-SPX in AC-4 [15] derived from SBR SBR transposition of bandlimited waveform, adapted © 2016-17 DOLBY LABORATORIES, INC. 37 from [25]. SBR Reconstruction

1. Transposition

2. Envelope adjustment

3. Tonality adjustment

 Sound example • Original (CD-quality) ~1.4 Mbps – BW = 22.050 kHz • AAC 48 kbps – BW 8.5kHz • aacPlus v1 (AAC+SBR) 48 kbps – BW = 16.193kHz – Compression ratio ~1:29

Output spectrum after SBR reconstruction, adapted © 2016-17 DOLBY LABORATORIES, INC. 38 from [25]. SBR Encoding

1. Extract parametric data • Cut-off frequency

– Depends on final bitrate, typically fc > 3-4 kHz • Spectral envelope • Tonality

2. Extract core waveform • Low-pass filtering • Down-sampling

3. SBC encoding of core waveform • AAC, mp3

4. Bitstream multiplexing • Encoded waveform + parametric data

Outline of an SBR encoder. © 2016-17 DOLBY LABORATORIES, INC. 39 SBR Decoding

1. Bitstream demultiplexing • encoded waveform • SBR data

2. Decode core waveform

3. SBR reconstruction • Transposition of core waveform • Envelope adjustment of reconstructed frequencies • Tonality adjustment through addition of sinusoids and noise

 Details follows in the upcoming slides…

Outline of an SBR decoder. © 2016-17 DOLBY LABORATORIES, INC. 40 SBR: core decoding

1. Perform decoding of core waveform

Core waveform decoding. © 2016-17 DOLBY LABORATORIES, INC. 41 SBR: waveform analysis

1. Perform decoding of core waveform

2. Analyze core waveform in a QMF filterbank

QMF analysis of core waveform. © 2016-17 DOLBY LABORATORIES, INC. 42 SBR: sub-band transposition

1. Perform decoding of core waveform

2. Analyze core waveform in a QMF filterbank

3. Transpose the QMF sub-bands

Transposition of the core waveform QMF bands. © 2016-17 DOLBY LABORATORIES, INC. 43 SBR: envelope adjustment

1. Perform decoding of core waveform

2. Analyze core waveform in a QMF filterbank

3. Transpose the QMF sub-bands

4. Adjust the spectral envelope of the transposed QMF bands to match the original envelope

Envelope adjustment of transposed QMF bands. © 2016-17 DOLBY LABORATORIES, INC. 44 SBR: sinusoids and noise

1. Perform decoding of core waveform

2. Analyze core waveform in a QMF filterbank

3. Transpose the QMF sub-bands

4. Adjust the spectral envelope of the transposed QMF bands to match the original envelope

5. Add additional sinusoids and noise to match the tonality of the original signal

Add sinusoids and noise if necessary. © 2016-17 DOLBY LABORATORIES, INC. 45 SBR: waveform synthesis

1. Perform decoding of core waveform

2. Analyze core waveform in a QMF filterbank

3. Transpose the QMF sub-bands

4. Adjust the spectral envelope of the transposed QMF bands to match the original envelope

5. Add additional sinusoids and noise to match the tonality of the original signal

6. Sample rate conversion of core QMF bands and waveform synthesis of the output signal in a synthesis filterbank

Waveform synthesis. © 2016-17 DOLBY LABORATORIES, INC. 46 Parametric Stereo (PS)

• Problem: available bitrate is still too low

• Idea • Stereo vs. Mono – Mono: half the bitrate for a given “Signal-to- Quantization-Error-Ratio” • “Reconstruct” stereo from a decoded mono down- mix with parameters estimated by the encoder

• Solution: Parametric Stereo [15] • Developed by Coding Technologies • ~2-3 kbps of parametric data • Enhanced aacPlus (aacPlus v2) – SBC (AAC core) + SBR + PS • A-CPL in AC-4 [15] derived from PS

Outline of a generalized PS encoder, adapted from [26]. © 2016-17 DOLBY LABORATORIES, INC. 47 PS: coding principle

• Encoding • Estimate intensity and correlation properties of the stereo channels – Inter-channel Intensity Difference (IID) -> “pan” – Inter-Channel Correlation (ICC) -> “ambience”

• Down-mix stereo to mono M – Typically

• Decoding • Reconstruct channel intensities through the IID • Decorrelate channel signals through all-pass filters estimated from the ICC

Parametric view of stereo signals, adapted from [26]. © 2016-17 DOLBY LABORATORIES, INC. 48 Combining SBR and PS

 Sound example • Original (CD-quality) ~1.4 Mbps – BW = 22.050 kHz • AAC 24 kbps – BW = 6.6 kHz • aacPlus v1 (AAC+SBR) 24 kbps – BW = 12.748 kHz • aacPlus v2 (AAC+SBR+PS) 24 kbps – BW = 14.815 kHz – Compression ratio ~1:59

 Conclusions • If the bitrate is too low for SBC coding – Form a hybrid codec with SBC and SBR • If the bitrate is too low for SBR+SBC coding

– Form a hybrid codec with SBC and SBR+PS Outline of a hybrid decoder with both SBR and PS, © 2016-17 DOLBY LABORATORIES, INC. 49 adapted from [26]. Summary & Remarks

 Psychophysical models  Lossy compression codecs for audio, video and images can benefit from psychophysical models derived from observed limitations in human perception

 Parametric coding  Parametric coding algorithms may offer substantial bitrate reductions when combined with core codecs that are unsuitable for further bitrate reductions  The use of a core codec (AAC, HEVC/AVC) in combination with an enhancement codec (SBR/PS, EDR) may offer backwards compatibility with devices only capable of decoding the core signal

 Increased system efficiency at the expense of increased complexity  May offer further bitrate reductions like in the case of multiple language representations in AC-4

 Quality measures  Subjective quality may vary among individuals and objective quality shall be measured in studies with blind-testing conditions [27] or with validated measurement algorithms [28]  The sound examples in this presentation are subject to bias and shall only be viewed as educational examples

© 2016-17 DOLBY LABORATORIES, INC. 50 Further Questions?

Dolby Laboratories Dolby Products Master’s Thesis Proposal Perceptual Audio Coding Abbreviations & Keywords

A-CPL Advanced CouPLing HE-AAC High-Efficiency AAC (aacPlus) A-SPX Advanced SPectral eXtension HEVC High-Efficiency Video Coding AAC Advanced Audio Coding HF High-Frequency ATG Advanced Technology Group (Dolby Laboratories) IIC Inter-Channel Correlation AVC Advanced Video Coding IID Inter-channel Intensity Difference BW BandWidth kbps KiloBits Per Second CMU Content Mapping Unit L Left (multi-channel audio) -> Lfs Left Frount Surround (9.1) CRT Cathode Ray Tube Lrs Left Rear Surround (7.1, 9.1) DD+ Dolby Digital Plus Ls Left Surround (5.1) EDR Extended Dynamic Range (Dolby Vision) Lss Left side surround (7.1, 9.1) EOTF Electro-Optical Transfer Function Mbps MegaBits Per Second EQ EQualizer (audio) MDCT Modified Discrete Cosine Transform HDR High Dynamic Range MTG Music Technology Group (UPF)

© 2016-17 DOLBY LABORATORIES, INC. 52 Abbreviations & Keywords

PCM Pulse-Code Modulation SBC Sub-Band Coding PQ Perceptual Quantizer (Dolby Vision) SBR Spectral Band Replication PQF Polyphase Quadrature Filter(s) SDR Standard Dynamic Range PS Parametric Stereo SMPTE Society of Motion Picture and Television Engineers Q-error Quantization error (“noise + distortion”) SQNR Signal-to-Quantization-Noise-Ratio Q-noise Quantization noise STFT Short-Time Fourier Transform QMF Quadrature Mirror Filter(s) UPF Universitat Pompeu Fabra (Barcelona, Spain) R Right (multi-channel audio) WCG Wide Color Gamut R&D Research & Development RF Radio-Frequency Rfs Right Front Surround (9.1) -> critical bandwidth (psychoacoustics) Rrs Right Rear Surround (7.1, 9.1) -> spectral/simultaneous masking (psychoacoustics) Rs Right Surround (5.1) Rss Right Side Surround (7.1, 9.1)

© 2016-17 DOLBY LABORATORIES, INC. 53 Links & References

1. R. Dolby, “An Audio Noise Reduction System”, Journal of the Audio Engineering Society, October 1967, Vol. 15, p.383-388

2. https://www.dolby.com/us/en/about/leadership/ray-dolby-walk-of-fame.html (URL 2017/02/16)

3. https://www.dolby.com/us/en/technologies/dolby-voice.html (URL 2017/02/16)

4. https://www.dolby.com/us/en/professional/products/dolby-conference-phone.html (URL 2017/02/16)

5. https://www.dolby.com/us/en/technologies/cinema/dolby-atmos.html (URL 2017/02/16)

6. https://www.dolby.com/us/en/professional/cinema/products/dolby-atmos-next-generation- audio-for-cinema-white-paper.pdf (URL 2017/02/16)

7. https://www.dolby.com/us/en/brands/dolby-vision.html (URL 2017/02/16)

© 2016-17 DOLBY LABORATORIES, INC. 54 Links & References

8. https://www.dolby.com/us/en/technologies/dolby-vision/dolby-vision-white-paper.pdf (URL 2017/02/16)

9. https://www.dolby.com/us/en/technologies/dolby-vision/the-art-of-better-pixels.pdf (URL 2017/02/16)

10. https://www.dolby.com/us/en/platforms/dolby-cinema.html / (URL 2017/02/16)

11. http://www.dolby.com/us/en/technologies/home/dolby-atmos.html (URL 2017/02/03)

12. https://www.dolby.com/us/en/technologies/dolby-atmos/dolby-atmos-for-the-home- theater.pdf (URL 2017/02/16)

13. https://www.dolby.com/uploadedFiles/wwwdolbycom/Content/Gutter/dolby-atmos-for- sound-bar-applications.pdf (URL 2017/02/16)

14. https://www.dolby.com/us/en/brands/dolby-audio.html (URL 2017/02/16)

© 2016-17 DOLBY LABORATORIES, INC. 55 Links & References

15. K. Kjörling et al., “AC-4 – The Next Generation Audio Codec”, 140th AES Convention, Paris, June 4–7, 2016

16. H. Purnhagen et al., “Immersive Audio Delivery Using Joint Object Coding”, 140th AES Convention, Paris, June 4–7, 2016

17. J. Larsen and M. Wolters, “Development Tools for Modern Audio Codecs”, 140th AES Convention, Paris, June 4–7, 2016

18. https://www.dolby.com/uploadedFiles/wwwdolbycom/Content/Technologies/AC-4/Dolby-AC-4- Audio-System-for-Next-Generation-Broadcast-Services.pdf (URL 2017/02/16)

19. https://www.dolby.com/us/en/technologies/ac-4/Next-Generation-Entertainment- Services.pdf (URL 2017/02/16)

20. https://www.dolby.com/us/en/technologies/dolby-pc-entertainment-experience-v4- overview.pdf (URL 2017/02/16)

© 2016-17 DOLBY LABORATORIES, INC. 56 Links & References

21. http://www.sf.se/biografer/Stockholm---Filmstaden-Scandinavia/Dolby-ATMOS/ (URL 2017/02/07)

22. https://www.dolby.com/us/en/star-wars/index.html (URL 2017/02/16)

23. https://www.dolby.com/us/en/guide/7.1.6-dolby-atmos-enabled-speaker-setup-guide.pdf (URL 2017/02/17)

24. E. Zwicker and H. Fastl, “Psychoacoustics – Facts and Models”, Third Edition. Springer. 2007. pages 17, 64.

25. M. Dietz et al., “Spectral Band Replication, a Novel Approach in Audio Coding”, 112th AES Convention, Munich, May 10-13, 2002

26. H. Purnhagen, “Low Complexity Parametric Stereo Coding in MPEG-4,” in Proc. 7th Int. Conf. Digital Audio Effects (DAFx’04), Naples, October 5-8, 2004

© 2016-17 DOLBY LABORATORIES, INC. 57 Links & References

27. International Telecommunications Union, “Method for the Subjective Assessment of Intermediate Quality Level of Audio Systems”, Rec. ITU-R BS.1534-3 (10/2015)

28. International Telecommunications Union, “Method for Objective Measurements of Perceived Audio Quality”, Rec. ITU-R BS.1387-1 (11/2001)

© 2016-17 DOLBY LABORATORIES, INC. 58