Direct Stream Digital

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Direct-Stream Digital
Media type Audio recording process
Disc format
Encoding Digital
Read mechanism DSD
Write mechanism Super Audio CD
Developed by Sony
Philips
Usage Audio recording
Extended from 1999
Extended to present

Direct-Stream Digital (DSD) is the trademark name used by Sony and Philips for their system of digitally recreating audible signals for the Super Audio CD (SACD). Practical DSD conversion was pioneered by Andreas Koch and Ed Meitner of EMM Labs. Koch and Jonathan Tinn later founded Playback Designs, who pioneered the transfer of DSD files over USB connections.[2] DSD technology was later developed and commercialized by Sony and Philips. However, Philips later sold its DSD tool division to Sonic Studio, LLC in 2005 for further development.

DSD uses pulse-density modulation encoding—a technology to store audio signals on digital storage media that are used for the Super Audio CD (SACD). The signal is stored as delta-sigma modulated digital audio; a sequence of single-bit values at a sampling rate of 2.8224 MHz (64 times the CD Audio sampling rate of 44.1 kHz, but only at 1⁄32,768th its 16-bit resolution). Noise shaping occurs by use of the 64× oversampled signal to reduce noise/distortion caused by the inaccuracy of quantization of the audio signal to a single bit. Therefore it is a topic of discussion whether it is possible to eliminate distortion in 1-bit Sigma-Delta conversion.[3]

DSD-CD has been marketed as an audiophile medium, primarily in Hong Kong with music by Cantopop artists such as Sally Yeh.[1] DSD technology may also have potential for video applications. A similar structure based on pulse-width modulation, which is decoded in the same way as DSD, has been used in Laserdisc video.[citation needed]

History

Development

DSD is a method of storing a Delta-Sigma signal before applying a "decimation" process that converts the signal to a PCM signal. When Delta-Sigma conversion was originally described in patent 2,927,962 filed by C. C. Cutler in 1954 (but not named as such until a 1962 paper by H. Inose, Y. Yasuda, and J. Murakami), decimation did not exist and the intention was to have oversampled data sent as-is. Indeed, the first proposal to decimate oversampled delta-sigma data to convert it into PCM audio did not appear until 1969, in D. J. Goodman's paper "The Application of Delta Modulation of Analog-to-PCM encoding".[4]

Practical DSD converter implementations were pioneered by Andreas Koch and Ed Meitner, the original founders of EMM Labs. Andreas Koch later left EMM Labs and along with Jonathan Tinn, founded Playback Designs who have pioneered the transfer of DSD files over USB connections.[2]

DSD technology was later developed and commercialized by Sony and Philips, the designers of the audio CD. However, Philips later sold its DSD tool division to Sonic Studio in 2005 for further development.[5]

Use of the format

See also: Super Audio CD
Major label support

DVD-Audio was endorsed by the Warner Music Group, while the SACD format was endorsed by Sony and Universal Music Group, with an especially high profile by UMG imprint Virgin Records.[6][7] Despite this, in 2011 The Warner Premium Sound series of albums was released by Warner Music Group, marking the first time the label released titled in a SACD format, with recording in DSD.[8] The series grew to ten rock and pop albums, with Super Audio CD/CD hybrid discs containing both an SACD layer and a standard CD layer.[9]

Sony didn't promote SACDs actively in North America, with the result that DVD-Audios gained competitive traction in the market. Elsewhere, such as in Europe or Japan, SACDs have gained more of a foothold.[10] Examples include the German Stockfisch Records, which releases vinyl editions of albums and DSD-recordings, released as hybrid SACDs.[11]

Independent label use

Many music companies that specialize in Super Audio CDs therefore sell products that have DSD encryption. A number of independent record labels have also worked directly with Sony to focus on DSD products or the DSD recording process.

DMP Digital Music Products was an early user of the SACD digital audio format.[12] In 1997 their release Alto by Joe Beck & Ali Ryerson was the first commercial recording captured with Sony's Direct Stream Digital recording technology. The label's Just Jobim by Manfredo Fest in 1998 was the first project captured with the new Meitner DSD conversion technology. In 2000, DMP released the world' s first multichannel SACD - Gaudeamus's Sacred Feast.[13]

The majority of Telarc International Corporation's releases are (generally hybrid) SACDs based on DSD recordings.[14] Telarc often works with early audiophile company Soundstream, and has re-released many of its original Soundstream recordings in SACD format, with a DSD-equivalent sampling rate of 50 kHz.[15]

The record label Mobile Fidelity had engineers who decided to adopt the Super Audio CD over the DVD-Audio disc as a high resolution digital format after listening tests and technical evaluations. On the label's Hybrid SACD releases, the SACD layer is a direct DSD recording of the analog master tape, while the CD layer is a digital down conversion of the DSD, with Super Bit Mapping applied. Post 2001 CD-only are sourced from DSD, but omit the SACD layer.[16]

Blue Coast Records was founded in California in 2007 for the purpose of recording and releasing music recorded with the DSD format, primarily focusing on jazz and acoustic artists.[17]

On Aug. 28, 2013, the Acoustic Sounds label launched SuperHiRez.com, which sells mainstream albums from major record labels that were produced with Direct Stream Digital or PCM audio formats.[18][19] On Sept. 4, 2013, Acoustic Sounds announced an agreement with Sony Music Entertainment to provide the company's new digital download service with albums that have been produced or remastered in Direct Stream Digital format.[20]

The format is used on albums such as Pop, Songs & Death in 2009,[21] and the remastered The Rolling Stones album Their Satanic Majesties Request in 2002.[22]

DSD technique

Comparison with PCM.

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.

A Direct Stream Digital (DSD) recorder uses sigma-delta modulation. DSD is 1-bit, has a sampling rate of 2.8224 MHz. The output from a DSD recorder alternates between levels representing 'on' and 'off' states, and is a binary signal (called a bitstream). The long-term average of this signal is proportional to the original signal. DSD makes use of noise shaping techniques in order to push quantization noise up to inaudible ultrasonic frequencies. In principle, the retention of the bitstream in DSD allows the SACD player to use a basic (one bit) DAC design which incorporates a low-order analog filter. The SACD format 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 and 20 kHz is the upper limit of human hearing.

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 96 kHz.[23] PCM sampled at 24 bits provides a (theoretical) additional 24 dB of dynamic range.

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) that 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 format with 24-bit resolution sampled at 352.8 kHz (or alternatively 384 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. 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. However, almost all present-day DAC chips employ some kind of sigma-delta conversion of PCM files that results in the same noise spectrum as DSD signals. (All SACD players employ an optional low-pass filter set at 50 kHz for compatibility and safety reasons, suitable for situations where amplifiers or loudspeakers cannot deliver an undistorted output if noise above 50 kHz is present in the signal.)

Double-rate DSD

The Korg MR-1000 1-bit digital recorder samples at 5.6448 MHz, twice the SACD rate. This is also referred to as DSD128 because the sample rate is 128 times that of CD. Since its establishment content creators have started to make 5.6 MHz DSD128 recordings available, such as the audiophile label Opus3.[24] Additionally a 48 kHz variant at 6.144 MHz has been supported by multiple hardware devices such as the exaSound e20 Mk II DAC.[25]

Quad-rate DSD

The Merging Technologies Horus AD/DA Converter offers sample rates up to 11.2 MHz, or four times the SACD rate. This is also referred to as DSD256 because the sample rate is 256 times that of CD. The Pyramix Virtual Studio Digital Audio Workstation allows for recording, editing and mastering all DSD formats, being DSD64 (SACD resolution), DSD128 (Double-DSD) and DSD256 (Quad-DSD). A 48 kHz variant of 12.288 MHz has been established.

Octuple-rate DSD

A further extension to the development of DSD is DSD512, with a sample rate of 22.5792 MHz (512 times that of CD), or alternatively 24.576 MHz (512 times 48 kHz). Hardware such as the Amanero Combo384 DSD output adapter,[26] and exaU2I USB to I2S Interface,[27] and software such as JRiver Media Player,[28] Foobar with SACD plugin,[29] and HQPlayer,[30] are all able to handle DSD files of this advanced sampling rate fully natively.

DSD playback options

Sony developed DSD for Super Audio CD and many disk players support SACD. Since the format is digital, there are other ways to play back a DSD stream; the development of these alternatives has enabled companies to offer high-quality music downloads in DSD.[31]

DSD disc format

Some professional audio recorders (from Korg, Tascam, and others) can record in DSD format. Transferring this signal to a recordable DVD with the appropriate tools, such as the 'AudioGate' software bundled with Korg MR-1/2/1000/2000 recorders, will render a DSD Disc. Such discs can be played back in native DSD only on certain Sony VAIO laptops and PlayStation 3.[32] HQPlayer from Feb 16 2011 ver 2.6.0 beta includes support for direct/native playback from DSDIFF (DSDIFF = DSD Interchange File Format) and DSF files (DSF = DSD Storage Facility) to ASIO devices with DSD support. Moreover, Sony produces two SACD-players, the SCD-XA5400ES and the SCD-XE800, that fully support the DSD-disc format. Only so-called DSF format is supported. DSF is a stereo-only, simplified form of DFF, the format used for SACD mastering and 5.1-channel downloads. However, since PCs (and Macs) have only PCM-audio hardware, DSD discs must be transcoded to PCM on the fly with the proper software plug-ins (for Windows Media Player or foobar2000), with questionable quality benefits compared to native high resolution PCM sources like DVD- or Blu-ray Disc Audio.

In June 2012, Pioneer launched a series of SACD players compatible with DSD-disc. The PD-10, PD-30 and PD-50.

In January 2013, TEAC announced a DSD-disc compatible player, the PD-501HR[33]

DSD over USB

An alternative to burning DSD files onto disks for eventual playback is to transfer the (non-encrypted) files from a computer to audio hardware over a digital link such as USB.

The USB audio 2.0 specification defined several formats for the more common PCM (Pulse-code modulation) approach to digital audio, but did not define a format for DSD.[34]

Playback Designs' players and converters[35] and pro-audio company Mytek Digital's 192 Stereo DAC both sport DSD over USB capability.[36]

In 2012 representatives from these companies and others developed a standard to represent and detect DSD audio within the PCM frames defined in the USB specification; the standard, commonly known as "DoP" standing for "DSD over PCM", is suitable for other digital links that use PCM.[34]

Many manufacturers are now offering DACs for sale which support the DoP standard. John Atkinson of Sterophile found with the pioneering Playback Designs DoP DAC /SACD player "The relatively high level of background noise limits the MPS-5's resolution with SACD and external 24-bit data to not much better than 16-bit CD.",[37] but it is considered likely that Mr. Atkinson's review of the MPS-5 reflects the performance of that model rather than the inherent performance of the DoP standard. At the time of writing, Stereophile has not yet published comparative test results from any other DoP-compatible product.

DSD-CD (CD-DA)

Sally Yeh's music has been marketed on DSD-CD in Hong Kong; DSD-CD's are simply CD-DAs derived from a DSD master.[1]

Despite its confusing name, DSD-CD is actually the same format as CD-DA. The difference from the standard version of CD is that the sound is assured to be derived from a DSD master. Other audio CDs, even those derived from DSD masters, are rarely marketed as DSD-CD. A DSD-CD however does not achieve the same sound resolution as SACD because the high-sample rate, low-resolution DSD sound has to be converted to 44.1 kHz, 16-bit PCM in order to be compliant with the 'Red Book' audio CD standard. DSD-CDs are fully compatible with CD.

DSD-CD has been marketed as an audiophile medium, primarily in Hong Kong with music by Cantopop artists such as Sally Yeh.[1]

DSD vs. PCM

There has been much controversy between proponents of DSD and PCM over which encoding system is superior. Professors Stanley Lipshitz and John Vanderkooy from the University of Waterloo, in Audio Engineering Society Convention Paper 5395 (2001), stated that 1-bit converters (as employed by DSD) are unsuitable for high-end applications due to their high distortion. Even 8-bit, four-times-oversampled PCM with noise shaping, proper dithering and half data rate of DSD has better noise floor and frequency response. However, in 2002, Philips published a convention paper arguing against this in Convention Paper 5616. Lipshitz and Vanderkooy's paper has been criticized in detail by Professor Jamie Angus at an Audio Engineering Society presentation in Convention Paper 5619 . Lipshitz and Vanderkooy responded in Convention Paper 5620.

There are fundamental distortion mechanisms present in the conventional implementation of DSD.[38] These distortion mechanisms can be alleviated to some degree by using digital converters with a multibit design. Historically, state-of-the-art ADCs were based around sigma-delta modulation designs. Oversampling converters are frequently used in linear PCM formats, where the ADC output is subject to bandlimiting and dithering (Hawksford 1995). Many modern converters use oversampling and a multibit design. It has been suggested that bitstream digital audio techniques are theoretically inferior to multibit (PCM) approaches: J Robert Stuart notes,[39] "1-bit coding would be a totally unsuitable choice for a series of recordings that set out to identify the high-frequency content of musical instruments, despite claims for its apparent wide bandwidth. If it is unsuitable for recording analysis then we should also be wary of using it for the highest quality work."

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 Erich-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."[40]

In the popular Hi-Fi press, it had been suggested that linear PCM "creates [a] stress reaction in people", and that DSD "is the only digital recording system that does not [...] have these effects" (Hawksford 2001). This claim appears to originate from a 1980 article by Dr John Diamond entitled Human Stress Provoked by Digitalized Recordings.[41] The core of the claim that PCM (the only digital recording technique available at the time) recordings created a stress reaction rested on "tests" carried out using the pseudoscientific technique of Applied Kinesiology, for example by Dr Diamond at an AES 66th Convention (1980) presentation with the same title.[42] Diamond had previously used a similar technique to demonstrate that rock music was harmful due to the presence of the "stopped anapestic beat".[43] Dr Diamond's claims regarding digital audio were taken up by Mark Levinson, who asserted that while PCM recordings resulted in a stress reaction, DSD recordings did not.[44][45][46]

A double-blind subjective test between high resolution linear PCM (DVD-Audio) and DSD did not reveal a statistically significant difference.[47] Listeners involved in this test noted their great difficulty in hearing any difference between the two formats.

The Future of DSD

DSD has not been broadly successful in the consumer markets, even though the SACD format has gained more traction than its direct competitor, DVD-Audio. DSD brings new challenges if immediate manipulation of the recorded data is desired. PCM is far easier to manipulate and is more easily built into existing applications such as the advent of very-high-resolution PCM media and tools e.g. DXD. DSD however is used as a master archive format in the studio market and seen as a possible low noise replacement for analog tapes. As a little quality is lost when converting from DSD to PCM and as PCM cannot be converted back into true DSD, the debate continues as to whether the ultimate quality digital audio can be found by using DSD players or recording directly into a high quality PCM format in the first place.

See also

References

  1. ↑ 1.0 1.1 1.2 "What is DSD-CD?". PS3SACD.com. Retrieved September 1, 2009. 
  2. ↑ 2.0 2.1 Playback Designs
  3. ↑ Stanley P. Lipshitz; John Vanderkooy (2001-05-12), Why 1-Bit Sigma-Delta Conversion is Unsuitable for High-Quality Applications, Audio Engineering Society, retrieved 2011-07-06 
  4. ↑ Data Converter Architectures Chapter 3 page 3.136 references these papers. Retrieved June 10, 2009
  5. ↑ Sonic Studio, LLC
  6. ↑ Genesis on SACD: Nick Davis interview. Retrieved 2011-11-03.
  7. ↑ Genesis Reviews|SACD. Retrieved 2011-11-03.
  8. ↑ Eagles, Deep Purple, Yes! Out-Of-Print DVD-Audios Coming To SACD. Retrieved 2011-11-03.
  9. ↑ Mobile Fidelity SACD catalogue. Retrieved 2011-11-03.
  10. ↑ DVD-A.net Retrieved 2011-11-03.
  11. ↑ "Stockfisch-Records". Stockfisch-records.de. Retrieved 2013-07-13. 
  12. ↑ 2004 Stereophile Magazine interview with Tom Jung
  13. ↑ Internet Archive of DMP Records
  14. ↑ Official site
  15. ↑ Jack Renner, The Roots of Telarc, Telarc newsletter, Fall 1992
  16. ↑ Enjoy the Music: "Enjoy the Music", accessed Nov. 12, 2010
  17. ↑ Clark, Rick (May 1, 2004). "5.1 Recording Vibes With ESE". Mix. Retrieved 2013-11-19. 
  18. ↑ Gordon Brockhouse, "Acoustic Sounds Launches Hi-Res Download Service", MarketNews Aug. 28, 2013
  19. ↑ Mike Snider, "Kansas firm raises bar on high-res music downloads" USA TODAY, Aug. 28, 2013
  20. ↑ Michael Lavorgna "Acoustic Sounds Announces DSD Deal with Sony Music!" AudioStream.com Sept. 4, 2013
  21. ↑ "Wheatus' new record downloadable in DSD". PS3SACD.com. July 24, 2009. Retrieved August 4, 2009. 
  22. ↑ Walsh, Christopher (24 August 2002). "Super audio CDs: The Rolling Stones Remastered". Billboard (Billboard). p. 27. 
  23. ↑ Extremetech.com, Leslie Shapiro, July 2, 2001. Surround Sound: The High-End: SACD and DVD-Audio. "Bottom line, SACD recordings can achieve a high-frequency response of 50kHz and a dynamic audio range of 120dB" Retrieved on June 10, 2009.
  24. ↑ Audiophile label Opus3 starts offering 5.6448MHz DSD downloads
  25. ↑ "exaSound e20 Mk II". 
  26. ↑ "OEM Combo384 Module - USB class 2 to I2S 32bit and DSD output Adapter". 
  27. ↑ "exaU2I - Multi-Channel Asynchronous USB to I2S Interface". 
  28. ↑ "exaSound e20 DSD256 Update". 
  29. ↑ "Foobar 2000 for Dummies (Part 2)". 
  30. ↑ "HQPlayer - upsampling multichannel audio player for Windows, Linux and OS X". 
  31. ↑ David W. Robinson (April 2012). "The Higher End: From an Editor's Notebook - Downloadable DSD". Positive Feedback Online. Retrieved 2012-05-14. 
  32. ↑ "PS3 SACD FAQ". PS3SACD.com. Retrieved August 8, 2010. 
  33. ↑ CES 2013 Annoucement
  34. ↑ 34.0 34.1 Andreas Koch et al (2012-03-30). "Method for transferring DSD Audio over PCM Frames Version 1.1". DSD-Guide.com. Archived from the original on 2012-05-14. Retrieved 2012-05-14. 
  35. ↑ Playback Designs
  36. ↑ Mytek Digital
  37. ↑ Atkinson, John. "Playback Designs MPS-5 SACD/CD player Measurements". Stereophile. 
  38. ↑ Hawksford, M. (2001). "SDM versus LPCM: The Debate Continues", 110th AES Convention, paper 5397.
  39. ↑ Coding for High-Resolution Audio Systems, J Robert Stuart, J. Audio Eng. Soc., Vol. 52, No. 3, March 2004 pp139-142
  40. ↑ 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 http://www.hfm-detmold.de/eti/projekte/diplomarbeiten/dsdvspcm/aes_paper_6086.pdf
  41. ↑ http://www.diamondcenter.net/digitalstress.html
  42. ↑ http://www.aes.org/e-lib/browse.cfm?elib=4408&rndx=461824
  43. ↑ Are the Kids All Right?: The Rock Generation and Its Hidden Death Wish, John Grant Fuller, ISBN0812909704, pp130-135
  44. ↑ http://www.acoust.rise.waseda.ac.jp/1bitcons/1bitforum2002/Mark.pdf
  45. ↑ http://www.redrosemusic.com/essay.shtml
  46. ↑ http://www.stereophile.com/images/newsletter/705Astph.html
  47. ↑ "DVD-Audio versus SACD". 

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