Super Audio CD
From Wikipedia, the free encyclopedia
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| Media type | Optical disc |
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| Encoding | Digital (DSD) |
| Capacity | up to 7.95 GiB/GB |
| Read mechanism | 650 nm laser |
| Developed by | Sony & Philips |
| Usage | Audio storage |
Super Audio CD (SACD) is a read-only optical audio disc format that can provide higher accuracy as well as surround sound compared to the audio CD format. Introduced in 1999, it was developed by Sony and Philips Electronics, the same companies that created the Compact Disc. SACD was in a format war with DVD-Audio.
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[edit] Overview
SACD is a disc of identical physical dimensions to the compact disc but it uses a very different technology from CD and DVD-Audio to encode its audio data, a 1-bit delta-sigma modulation process known as Direct Stream Digital at the very high sampling rate of 2.8224 MHz. This is 64 times the sampling rate used in Compact Disc Digital Audio (CDDA), which specifies 44.1 kHz at a resolution of 16-bit. Because the resolution of SACD is 16 times smaller than CDDA, the bitrate for a given channel is 4 times as large.
There are three types of SACDs:
- Hybrid: The most popular of the three types, hybrid discs include a "Red Book" layer compatible with most legacy Compact Disc players, dubbed the "CD layer," and a 4.7 GB SACD layer, dubbed the "HD layer." It is not uncommon for hybrid discs to carry the "Compact Disc Digital Audio" logo to show that the disc is CDDA-compliant.
- Single-layer: Physically a DVD-5 DVD, a single-layer SACD includes a 4.7 GB HD layer with no CD layer.
- Dual-layer: Physically a DVD-9 DVD, a dual-layer SACD includes two HD layers totalling 8.5 GB, with no CD layer. This type is rarely used. It enables nearly twice as much data to be stored, but eliminates CD player compatibility.
SACD authoring guidelines suggest that an SACD should always contain a 2-channel stereo mix[citation needed] though not all SACD have it (for example, in 2005 Sony Music Entertainment (Germany) GmbH released Charles Rosen's performance of the Goldberg Variations as a hybrid SACD with 16-bit PCM and DSD 5.1 surround but no DSD stereo). They may optionally contain a surround mix — either 5.0 or 5.1 layout. Although the disc always stores all channels, the surround mix does not have to use them all, and some may be mute; for example the 2001 SACD release of Mike Oldfield's Tubular Bells remains in the quadraphonic 4.0 mix made in 1975, and the RCA reissue of the 1957 Chicago Symphony Orchestra recording of Mussorgsky's Pictures at an Exhibition marks the first time the original 3.0 (three track) recording is available in a consumer format. The correct designation for the surround part of an SACD is "multi-channel", and usually has either the label "SACD Surround" or its own "Multi-Ch" logo on the back cover.
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[edit] Market forces
The standard redbook CD continues to be the mainstream optical disk format for audio, mainly competing on price and the large installed base of compatible players. As all SACD players can play older CD issues, and since almost all SACD discs are now issued as hybrids (playable on both on older CD players and newer SACD machines), the new SACD format essentially nests the older CD format (rather than competing with it).
Although SACD and the traditional LP record both may have minuscule shares of the total market, SACD has gained significant momentum within certain genres. SACD is strong within classical, jazz and acoustic music, genres that appeal to the audiophile or high fidelity community. In the more general music market, the dominant market force now appears to be convenience: the rise of digital downloads, in particular lower-quality mp3 files (partly fed by widely-available pirated content), and the decline in older CD format sales. Accordingly, what appears to be emerging is a dichotomous market structure of extremes: the mass market is moving toward a lower-quality convenience model, while the high-end audiophile market has seen a recent resurgence through the SACD format. As of March 2009, there are in excess of 5,000 SACD titles on the market.[1]
[edit] DVD-Audio
DVD-Audio was a format with somewhat similar features as SACD, but sales seems to have stagnated below the 2001-level[4].
[edit] Blu-ray
BD-Audio is a newer format that uses the Blu-ray Disc physical format for high-resolution, multichannel audio-only playback, but there has yet to be any music industry support for Blu-ray as an audio format.
[edit] Downloads
There is no inherent reason why downloads must be of lower quality, other than the higher time to download larger files. For example, sixty minutes of typical CD quality audio contains an average of about 660 MB of uncompressed data or about 350 MB of data processed with lossless compression, an mp3 version of it might be 60 to 240 MB depending on compression quality, whereas an SACD disc would allows 5 gigabytes of data (though this may also be compressed losslessly if downloaded). Given the popularity of non-physical media distribution such as iTunes, some[2] think that physical media will lose market share to downloadable media, even in the high fidelity market. FLAC media files with data rates equalling that of physical media are available from niche record companies.[3][4]. However, there are a number of significant obstacles to be overcome before high-quality downloads can practically be perceived to threaten the market position of SACD. First, almost all computers ship with 44.1/48KHz D/A converters, and unless special sound cards are purchased, standard computers cannot reproduce 96KHz or 192 KHz hi-res recordings. Second, the downloaded tracks cannot currently be played or supported within mainstream media players such as iTunes; the Windows MediaPlayer can support up to 96KHz provided the computer has a sound card capable of 96 KHz D/A conversion. Third, there are only a tiny number of titles available for download: for example, as of March 2009, there are less than 50 hi-res classical titles that have been licensed. Fourth, because these downloads exist outside of iTunes and Windows Media Player, there is no widespread DRM management system available to protect music industry property rights. This acts as something of a 'catch 22': almost all hi-res downloads that are available in March 2009 are free of DRM restrictions, and equally, the same freedom may explain the unwillingness of content owners to license their content. Fifth, the SACD format has not been cracked, and SACD recordings are not available as downloads. DSD files are not offered as they are not playable on personal computers.
[edit] Integration
As of February 2008, there have been over 5,000 SACD releases, slightly more than 50% of which appear to be classical. Jazz and popular music albums, mainly remastered previous releases, are the next two most common genres released to date.[5][6] Notable popular artists who have released some or all of their back catalog include Alice In Chains, Aerosmith, Björk, Black Sabbath, Boston, David Bowie, Carpenters, Hiromi, Depeche Mode, Bob Dylan, Peter Gabriel, Genesis, Billie Holiday, Elton John, The Moody Blues, The Rolling Stones, Eleanor McEvoy, The Offspring, Nine Inch Nails, Santana, and Barbra Streisand. Pink Floyd's seminal album The Dark Side of the Moon (the 30th anniversary edition of 2003), The Who's seminal album Tommy (the 34th anniversary edition of 2003), and Roxy Music's Avalon (the 21st anniversary edition, 2003) were released on SACD to take advantage of the format's multi-channel capability. All three were remixed in 5.1 surround, and released as Hybrid SACDs with a stereo mix on the standard CD layer.
Because most SACDs are issued in a hybrid format, such as the remastered Rolling Stones and Bob Dylan albums released in 2002, music collectors may build and enjoy an SACD collection even if their only disc player is not designed to read the SACD's higher fidelity DSD encoding. The ability to play SACD hybrid discs on all standard Red Book CD or DVD video players is considered a significant advantage of the SACD format over DVD-Audio. Today, there are many affordable "universal" multiformat players which play not only SACD but also competing formats DVD-Audio or DualDisc.
Despite relatively wide consumer availability to SACD players, however, high definition audio formats continue to attract few major record labels. This is, in part, because, in the mid-2000s, the major labels such as Universal adopted a downmarket marketing strategy of (a) seeking mega-sales from a tiny number of releases (typically cross-over discs such as a classical star performing tangos), and (b) increased their marketing of low-cost compressed audio formats. With the major labels vacating the high-end long tails of the market and failing to address market niches, dozens of smaller companies have entered the market in the last few years to cater for audiophile and classical enthusiasts. As of March 2009, over 440 labels have released one or more SACDs, giving the classical market place a dynamic and youthful energy that is probably unprecedented since the launch of the CD itself. Indeed, the latest trend is for major league orchestras / groups to release their own in-house labels (e.g. the Chicago Symphony Orchestra's highly regarded and multi-award winning new Chicago Resound label provides full support for hi-resolution SACD hybrid disks, as does the London Symphony Orchestra's 'LSO Live' label [7]).
[edit] Disc reading
Objective lenses in conventional CD players have a longer working distance, or focal length, than lenses designed for SACD players. This means that when a hybrid SACD is placed into a conventional CD player, the laser beam passes the high-resolution layer and is reflected by the conventional layer at the standard 1.2 mm distance, and the high-density layer is out of focus. When the disc is placed into an SACD player, the laser is reflected by the high-resolution layer (at 600 µm distance) before it can reach the conventional layer. Conversely, if a conventional CD is placed into an SACD player, the laser will read the disc without difficulty since there is no high-resolution layer.
[edit] Playback hardware
Hybrid Super Audio CDs (which include both a Stereo CD and a Super Audio CD layer) can be played back on CD players. To hear the Super Audio CD Stereo, and on many discs the Super Audio CD Multichannel layer, requires a Super Audio CD player.
As would be expected, Sony and Philips – designers of the CD and SACD formats – have the most players on the market in many guises such as standalone players, combined DVD/SACD players, in-car players,[8].
The Sony SCD-1 was a player which was introduced concurrently with the SACD format in 1999 for a price of approximately US$5,000.[9] It weighs over 26 kg (57 lb). The SCD-1, no longer produced, was introduced before multi-channel SACDs existed and plays two channel SACDs and Red Book CDs only.
Many other electronics manufacturers, including Denon/Marantz, Pioneer, Yamaha offer SACD playback capabilities throughout their product lines. None, however, has offered a portable SACD player capable of playing the high definition layer of an SACD. Most portable CD players will play the conventional CD layer of a Hybrid SACD.
SACD players are not permitted to digitally output an unencrypted stream of DSD. Players initially supported only analog output; later some proprietary digital interfaces such as Denon Link permitted encrypted transmission of DSD. There are now two standard digital connection methods capable of carrying DSD in encrypted form: i.Link and HDMI (version 1.2 or later, standardised in August 2005).
The older i.Link interface is generally found on older mid- to high-end equipment and some current top of the line units from the Japanese manufacturers. HDMI is more common, being the standard digital connection method for high-definition video+audio. Most new mid-level and higher 2007 model year and later A/V processors support the HDMI 1.2 specification's DSD over HDMI feature. Most boutique manufacturers still do not support DSD. Some HDMI 1.1 spec DVD players convert DSD to LPCM and then pass it to an HDMI 1.1 spec or later processor. Lower end processors usually convert the DSD to LPCM, higher end ones usually convert it to LPCM for bass management or DSP but can also process it natively at the expense of DSP and bass management. Some new DVD players from Oppo Digital, Pioneer, Onkyo, etc. now support HDMI 1.2 or 1.3 and will pass DSD over HDMI as well as LPCM. Be aware that some players, for instance, Onkyo DV-SP504, will not support DSD or LPCM over HDMI without resampling it to 48 kHz. SACD or DVD-A will be played through analog outputs instead. The older i.Link interface has been dropped from all but high end A/V processors and DVD players.
Some players, such as the PlayStation 3 (not the 40GB version), do not output DSD over HDMI, but instead convert it to PCM.
[edit] PlayStation 3 and SACD playback
The first two generations of Sony's PlayStation 3 game console are capable of reading SACD discs. Starting with the third generation (introduced October/November 2007), SACD playback was removed altogether. [10]
For models that are capable of reading SACD, three output options exists.
- Using the AV output will give an analog stereo sound for SACDs that include a stereo track.
- Using HDMI will give access to multichannel high-resolution PCM audio (converted from DSD).
- Using S/PDIF will give digital stereo sound[A] (of either the stereo track, or a down-mix of the surround track)
- A PS3 was capable of converting surround DSD to lossy 1.5 Mbit/s DTS for playback over S/PDIF using the 2.00 software. The immediate revision after that removed the feature.[11]
[edit] DSD
SACD audio is stored in a format called Direct Stream Digital (DSD), which differs from the conventional PCM used by the compact disc or conventional computer audio systems.
DSD is 1-bit, has a sampling rate of 2.8224 MHz, and makes use of noise shaping quantization techniques in order to push 1-bit quantization noise up to inaudible ultrasonic frequencies. This gives the format a greater dynamic range and wider frequency response than the CD. Promotional materials about SACD supplied by Philips and Sony suggest that the system is capable of delivering a dynamic range of 120 dB from 20 Hz to 20 kHz and an extended frequency response up to 100 kHz, although most currently available players list an upper limit of 80–90 kHz.
The process of creating a DSD signal is conceptually similar to taking a 1-bit delta-sigma analog-to-digital (A/D) converter and removing the decimator which converts the 1-bit bitstream into multibit PCM. Instead, the 1-bit signal is recorded directly and in theory only requires a lowpass filter to reconstruct the original analog waveform. In reality it is a little more complex, and the analogy is incomplete in that 1-bit sigma-delta converters are these days rather unusual, one reason being that a 1-bit signal cannot be dithered properly: most modern sigma-delta converters are multibit.
Because of the nature of sigma-delta converters, one cannot make a direct comparison between DSD and PCM. An approximation is possible, though, and would place DSD in some aspects comparable to a PCM format that has a bit depth of 20 bits and a sampling frequency of 192 kHz. PCM sampled at 24 bits provides a (theoretical) additional 24 dB of dynamic range. Due to the effects of quantization noise, the usable bandwidth of the SACD format is approximately 100 kHz, which is similar to 192 kHz PCM.
Because it has been extremely difficult to carry out DSP operations (for example performing EQ, balance, panning and other changes in the digital domain) in a 1-bit environment, and because of the prevalence of studio equipment such as Pro Tools, which is solely PCM-based, the vast majority of SACDs — especially rock and contemporary music which relies on multitrack techniques — are in fact mixed in PCM (or mixed analog and recorded on PCM recorders) and then converted to DSD for SACD mastering.
To address some of these issues, a new studio format has been developed, usually referred to as "DSD-wide", which retains standard DSD's high sample rate but uses an 8-bit, rather than single-bit digital word length, but still relies heavily on the noise shaping principle. It becomes almost the same as PCM (it's sometimes disparagingly referred to as "PCM-narrow") but has the added benefit of making DSP operations in the studio a great deal more practical. The main difference is that "DSD-wide" still retains 2.8224 MHz (64Fs) sampling frequency while the highest frequency in which PCM is being edited is 352.8 kHz (8Fs). The "DSD-wide" signal is down-converted to regular DSD for SACD mastering. As a result of this technique and other developments there are now a few digital audio workstations (DAWs) which operate, or can operate, in the DSD domain, notably Pyramix and some SADiE systems.
Another format for DSD editing is DXD (Digital eXtreme Definition), a "PCM-like" signal with 24-bit resolution sampled at 352.8 kHz.
Note that high-resolution PCM (DVD-Audio, HD DVD and Blu-ray Disc) and DSD (SACD) may still technically differ at high-frequencies. A reconstruction filter is typically used in PCM decoding systems, much the same way that bandwidth-limiting filters are normally used in PCM encoding systems. Any error or unwanted artifact introduced by such filters will typically affect the end-result. If the filter designer choose a wide, flat passband, then the length of the impulse response will inevitably increase ( Time-domain analysis of filters). A claimed advantage of DSD is that product designers commonly choose to have no filtering, or modest filtering. Instead DSD leads to constant high levels of noise at these frequencies. DSD's dynamic range decreases quickly at frequencies over 20 kHz due to the use of strong noise shaping techniques which push the noise out of the audio band resulting in a rising noise floor just above 20 kHz. PCM's dynamic range, on the other hand, is the same at all frequencies. (Some high-end SACD players employ an optional low-pass filter set at 30 kHz for compatibility and safety reasons, suitable for situations where amplifiers or loudspeakers can't deliver an undistorted output if noise above 30 kHz is present in the signal.)
[edit] DST
To reduce the space and bandwidth requirements of DSD (2.8 Mbit/s per channel), a lossless data compression method called Direct Stream Transfer (DST) is used — DST compression is compulsory for multi-channel regions and optional for stereo regions. This typically compresses by a factor of between two and three, allowing a disc to contain 80 minutes of both 2-channel and 5.1-channel sound.
[edit] Pit Signal Processing
SACD includes various copy protection measures of which the most prominent is Pit Signal Processing (PSP), a physical watermarking feature that contains a digital watermark modulated in the width of pits on the disc (data is stored in the pit length). The optical pickup must contain special circuitry to read the PSP watermark, which is then compared to information on the disc to make sure it's legitimate. Because the majority of DVD players and all DVD-ROM drives use an optical pickup that lacks this specialized watermark detection circuitry they cannot read the data on the SACD layer of a protected SACD disc.[12]
On hybrid SACD discs, PSP is only applied to the SACD layer — not to the CD layer.
[edit] Sound quality of SACD vs CD
In the audiophile community, SACD is generally considered to provide substantially higher quality compared to older format redbook CD recordings.
[edit] Getting "High resolution" sound reproduction
SACD has a superior bandwidth compared to CD, SACD has a superior signal to noise ratio compared to CD, and the increased media bitrate in itself is an argument for increased sound quality. The DSD technology behind SACD enables reproduction of sound in a way that is essentially identical to the studio master. Proponents argue that the medium offers greater clarity, depth and warmth than CD, with less harshness.
Not considering what humans can actually perceive, there are a number of requirements that must be in place for there to be any significant increase in playback precision in terms of frequency response and SNR when improving on CD specifications:
- The acoustic conditions in the recording area or high-frequency attenuation of air.
- The recording microphone and microphone preamplifier
- The A/D-converter
- Desirable and undesirable processing from the mixing/mastering process
- The distribution media (e.g. SACD)
- The D/A-converter
- The power amplifier
- The loudspeaker
- The listening room
If any one of those factors either contribute high levels of noise or high-frequency attenuation, then getting high SNR-values or accurate high-frequency response at the playback-site will be impossible.
[edit] Surround sound vs stereo
SACD allows for 5.1 channels of lossless, high-quality surround sound. This is impossible to achieve on a regular CD, and there is general agreement that surround sound has the potential for a different, and often better, subjective experience [13].
[edit] "High resolution" vs "normal resolution"
Producers of CD recordings are essentially free to master the content as they see fit. This has led to a so-called loudness-war, especially in popular music, where only a fraction of the available dynamic range of the CD medium is actually used. This is accomplished by artificially decreasing the natural dynamic range of instruments and performances using dynamic compression or even clipping.
Limitations in the SACD medium (specifically, the stability of the noise-shaping circuit) means that SACD cannot be mastered at such high levels. Some argue that this is a benefit of SACD, similar to how limitations of the gramophone record medium is said to have forced mastering engineers into making argueably "better" recordings than they would if unlimited by the medium.
On the other hand, popular music is the genre most heavily affected by the loudness war, and the largest part of SACD recordings are in the classical, jazz and acoustic genres that may not be as heavily affected by the loudness war irrespective of distribution medium.
Modern popular music is often compressed during mastering to a small percentage of the maximum available dynamic range, and thus would not significantly benefit from the extended dynamic range available in SACD without remastering the audio for more dynamics. However, electronic and organ music offer a wide natural dynamic range, and audiophiles benefit from the lack of amplitude compression that an extended dynamic range affords.
Improved quality may result from simply preventing the kinds of poor mastering sometimes found on CD, rather than from any fundamental audible difference between DSD and PCM.[14] PCM mastered several dB lower would also obtain the same benefit.
A 2007 article published in the Journal of the Audio Engineering Society reported the results of a study, which concluded that listeners could not hear the difference between a high-resolution two-channel recording and a CD-quality downsampling of the same recording except when "unpleasantly (often unbearably) loud."[14] The article concluded that many high-resolution releases sounded better than their CD counterparts, but attributes this to mastering differences.
[edit] Sound quality of DSD vs. (24-bit/176.4 kHz) PCM
When comparing a DSD and PCM recording of the same origin, the same number of channels and similar bandwidth/SNR, some still think that there are differences. A study conducted at the Erik-Thienhaus Institute in Detmold, Germany, seems to contradict this, concluding that "hardly any of the subjects could make a reproducible distinction between the two encoding systems. Hence it may be concluded that no significant differences are audible". [15]
[edit] Copy protection
SACD has several copy protection features at the physical level which, for the moment, appear to make SACD discs impossible to copy without resorting to the analog hole, or ripping of the conventional 700MB layer on hybrid discs. These include physical pit modulation and 80-bit encryption of the audio data, with a key encoded on a special area of the disk that is only readable by a licensed SACD device. The HD layer of an SACD disc cannot be played back on computer CD/DVD drives, nor can SACDs be created except by the licensed disc replication facilities in Shizuoka and Salzburg.[16]
It is possible to capture the DSD digital audio signal after the decryption stage right before the digital to analog converters of an SACD player, but since there is no practical way for the public to make their own SACDs, this does not pose a major threat.
The hacking of protection methods used on HD DVD and Blu-ray Disc, when they accounted for only 4% of digital movie sales in 2007, shows either that the latter formats are relatively insecure, or that market share creates not only the demand for technologies that enable consumers to bypass the protection but also the supply of same, or that the content on SACDs (predominantly audiophile Classical and Jazz) is simply inconsistent with the interests of hackers.
A number of new SACD players have encrypted IEEE 1394 (also called FireWire or i.Link) or HDMI digital outputs carrying DSD data, and it may be possible to get the raw DSD data from these links. The protection mechanism used is Digital Transmission Content Protection (DTCP), which can be used in "Copy Once" or "Copy Never" modes. It is unlikely, however, that the SACD license agreement rules permit anything but the "Copy Never" mode to be used.
There seems to be one solution for obtaining digital non-DRM output on SACD as well as DVD-A players. A Switzerland-based company is offering a modified output-board that taps into the digital datastream prior to D/A conversion as well as converting DSD to PCM that the S/PDIF port can transfer.[17]
[edit] See also
- Audio format
- Audio storage
- DualDisc
- DVD-Audio
- Media packs
- Earlier attempts at higher fidelity that stayed within the CDDA standard: XRCD and HDCD.
[edit] References
- ^ [1]
- ^ Spector CD Extinction
- ^ [2]
- ^ [3]
- ^ http://www.highfidelityreview.com/news/index.asp
- ^ http://www.amazon.com/s?url=search-alias%3Dpopular&field-keywords=SACD
- ^ http://lso.co.uk/buyrecordings/
- ^ "Sony Announces Three Super Audio CD Car Stereo Players". HighFidelityReview.com. http://www.highfidelityreview.com/news/news.asp?newsnumber=10972765. Retrieved on 2007-01-18.
- ^ "The Sony SCD-1 SACD Player". @udiophilia. http://www.audiophilia.com/hardware/sacd.htm. Retrieved on 2006-05-18.
- ^ "Why did Sony take SA-CD out of PS3 again?". http://www.ps3sacd.com/faq.html#_Toc180147568. Retrieved on 2009-01-04.
- ^ "PS3SACD.com News, November 22, 2007". http://www.ps3sacd.com/.
- ^ "Details of DVD-Audio and SACD". DVDdemystified.com. http://www.dvddemystified.com/dvdfaq.html#3.6.1. Retrieved on 2007-07-12.
- ^ Toole, E. Floyd (2008), Sound reproduction - Loudspeakers and rooms, Focal press, ISBN 9780240520094
- ^ a b Meyer, E. Brad; David Moran (September 2007). "Audibility of a CD-Standard ADA Loop Inserted Into High-Resolution Audio Playback". Journal of the Audio Engineering Society 55 (9).
- ^ DVD-Audio versus SACD: Perceptual Discrimination of Digital Audio Coding Formats; Blech, Dominic; Yang, Min-Chi. Erich-Thienhaus-Institute (Tonmeisterinstitut), University of Music Detmold, Germany 2004
- ^ "Sony Starts Hybrid Super Audio CD Production Facilities in Europe". SA-CD.net. 2003-01-22. http://www.sa-cd.net/shownews.php?news=6. Retrieved on 2007-07-12.
- ^ dvdupgrades.ch
[edit] Bibliography
- Janssen, E.; Reefman, D. "Super-audio CD: an introduction". Signal Processing Magazine, IEEE Volume 20, Issue 4, July 2003 Page(s): 83 - 90
[edit] External links
- SA-CD site at Sony Music
- puresuperaudio.blogspot.com (All about SACD and DSD)
- SA-CD.net SA-CD Reference (Includes full list of available albums and comprehensive FAQ)
- Multichannel SACD Rating: album guide for surround-sound lovers.
- PS3SACD.com FAQ: a dedicated FAQ about SACD functionality on PlayStation3
- Super Audio Compact Disc: A Technical Proposal (PDF), Sony.
- The SA-CD explained
- "Breaking the Sound Barrier: Mastering at 96 kHz and Beyond" (PDF) Audio Engineering Society Convention Paper 4357 on "HD" audio.
- "A Native Stereo Editing System for Direct-Stream Digital" (PDF) Audio Engineering Society Convention Paper 4719 on the 1st DSD commercial editor.
- "Why Direct Stream Digital is the best choice as a digital audio format" (PDF) Audio Engineering Society Convention Paper 5396.
- "Why 1-Bit Sigma-Delta Conversion is Unsuitable for High-Quality Applications" (PDF) Audio Engineering Society Convention Paper 5395.
- "DVD-Audio versus SACD: Perceptual Discrimination of Digital Audio Coding Formats" (PDF) Audio Engineering Society Convention Paper 6086.
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