Direct Stream Digital

Direct Stream Digital is a trademark used by Sony and Philips for their system for digitally encoding audio signals for the Super Audio CD.
DSD uses delta-sigma modulation, a form of pulse-density modulation encoding, a technique to represent audio signals in digital format, a sequence of single-bit values at a sampling rate of 2.8224 MHz. This is 64 times the CD audio sampling rate of 44.1 kHz, but with 1-bit samples instead of 16-bit samples. Noise shaping of the 64-times oversampled signal provides low quantization noise and low distortion in the audible bandwidth necessary for high resolution audio.
DSD is simply a format for storing a delta-sigma signal without applying a decimation process that converts the signal to a PCM signal.

Development

DSD technology was developed and commercialized by Sony and Philips, the designers of the audio CD. However, in 2005, Philips sold its DSD tool division to Sonic Studio.
;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. Despite this, in 2011, The Warner Premium Sound series of albums was released by Warner Music Group, marking the first time the label released titles in a SACD format, with recording in DSD. 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.
Sony did not promote SACD actively in North America, with the result that DVD-Audio gained competitive traction in the market. Elsewhere, such as in Europe or Japan, SACD gained more of a foothold. Examples include the German Stockfisch Records, which releases vinyl editions of albums and DSD-recordings, released as hybrid SACDs.
;Independent label use
Music companies that specialize in Super Audio CD products therefore use DSD encoding. 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. In 1997 their release Alto by Joe Beck & Ali Ryerson was the first commercial recording captured with Sony's DSD 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 multi-channel SACD—Sacred Feast by Gaudeamus.
The majority of Telarc International Corporation's releases were on SACD, and are DSD recordings. Telarc often worked with early audiophile company Soundstream, and re-released many of its original Soundstream recordings in SACD format. Soundstream, which made the first digital recording in the United States, recorded in 16-bit PCM at a sample rate of 50 kHz via its own proprietary digital recorder. This 50 kHz PCM format was converted to DSD for release on Telarc SACD.
The record label Mobile Fidelity had engineers who decided to adopt the SACD over the DVD-Audio disc as a favored 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 releases are sourced from DSD, but omit the SACD layer.
In 2007, Blue Coast Records was founded in California for the purpose of recording and releasing music recorded with the DSD format, primarily focusing on jazz and acoustic artists.
On August 28, 2013, the Acoustic Sounds label launched SuperHiRez.com, which sold mainstream albums from major record labels that were produced with Direct Stream Digital or PCM audio formats. On September 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 DSD format.
The format is used on albums such as Pop, Songs & Death in 2009, and the remastered The Rolling Stones album Their Satanic Majesties Request in 2002.

DSD signal format

DSD differs from the PCM format used by compact disc or typical computer audio systems: while PCM uses a multi-bit value at a low sample rate, DSD instead uses a single-bit value at a sample rate much higher than the signal's bandwidth.
The process of creating a DSD signal is the same as the front-end modulator and noise-shaper portion of a 1-bit delta-sigma analog-to-digital converter, without the back end decimator. The short-term average of the 1-bit DSD bitstream signal is proportional to the original signal amplitude. Because of the higher sample rate, an SACD player can use a one-bit DAC with a low-order analog filter to reconstruct and produce the analog output.
DSD uses noise shaping techniques to push quantization noise up to inaudible ultrasonic frequencies above 20 kHz. Because of this, single-rate DSD64 can deliver a dynamic range of 120 dB from 20 Hz to 20 kHz. SACD marketing also claimed an extended frequency response up to 100 kHz, but at those high frequencies any sound, if present, is drowning in ultrasonic noise generated by noise shaping. The practical limit is 20 or 30 kHz, where ultrasonic noise starts rising. Around 1999 when SACD premiered, amplifiers, headphones and speakers typically had a frequency response up to 20 kHz, and SACD players were supplied without any filtering, assuming speakers and headphones would not reproduce this ultrasonic noise. Later invention of super tweeters and extension frequency response of speakers and headphones up to 40 kHz and amplifiers up to 100 kHz motivated designers of SACD/DSD players to include a 24 kHz filter to block this noise at the output.
The various DSD formats use sampling rates well into the megahertz range, typically with an oversampling ratio that is a power of two relative to the 44.1 kHz rate used for CD audio:

Name	Abbreviation	Sample rate	Oversampling ratio relative to 44.1 kHz	Notes
Single-rate DSD	DSD64	2.8224 MHz	64×	The format used for SACD media.
Double-rate DSD	DSD128	5.6448 MHz	128×	Since its establishment, content creators have made DSD128 recordings available, such as the audiophile label Opus3.
Quad-rate DSD	DSD256	11.2896 MHz	256×	The format used by Mobile Fidelity for LP mastering
Octuple-rate DSD	DSD512	22.5792 MHz	512×
Sexdecuple-rate DSD	DSD1024	45.1584 MHz	1024×

See for analysis of the effective number of bits that can be achieved by oversampling, especially when using a higher order modulator.

DSD mixing and mastering

DSD music mixing and mastering for SACD or Internet download presents challenges due to the difficulty of performing digital signal processing operations in a one-bit environment.
Older analog recordings were processed using analog equipment and then digitized to DSD. It is also possible to avoid processing by using only the available adjustments in the studio equipment while recording to DSD.
One DSP technique available is to convert the DSD to PCM and use standard PCM equipment such as Pro Tools, useful for rock and contemporary music, which rely on multitrack techniques, then digitally convert back to DSD format. Some DSD proponents dislike this technique, claiming that the PCM conversion to a lower sample rate reduces the sound quality of DSD.
A format and set of tools for PCM processing of DSD has been developed under the name Digital eXtreme Definition. This is a PCM format with 24-bit resolution sampled at 352.8 kHz. Another DSP technique uses a format commonly referred to as DSD-wide, which retains the high sample rate of standard DSD, but uses 8-bit samples with noise shaping. DSD-wide is sometimes disparagingly referred to as PCM-narrow. It has the benefit of making DSP operations practical while retaining the 2.8224 MHz sampling frequency. The processed DSD-wide signal is converted to the final 1-bit DSD product at the same sample rate. Processing DSD-wide at the higher multiple-DSD sample rates is also possible. Pyramix and some SADiE digital audio workstation systems can operate in the DSD-wide domain.

DSD processing tools

DXD was initially developed for the Merging Technologies Pyramix workstation and introduced together with their Sphynx 2, AD/DA converter in 2004. This combination meant that it was possible to record and edit directly in DXD, and that the sample only converts to DSD once before publishing. This offers an advantage to the user as the noise created by converting DSD rises dramatically above 20 kHz, and more noise is added each time a signal is converted back to DSD during editing.
The Pyramix Virtual Studio Digital Audio Workstation allows for recording, editing and mastering all DSD formats up to DSD256. A 12.288 MHz DSD256 variant based on a 48 kHz reference is supported. The exaSound e20 DAC was the first commercially available device capable of DSD256 playback at sampling rates of 11.2896 or 12.288 MHz. The Merging Technologies Horus AD/DA Converter offers sample rates up to 11.2 MHz, or four times the SACD rate.
DSD128, 5.6448 MHz, twice the SACD rate, has been supported by multiple hardware devices such as the exaSound e20 Mk II DA,C Korg MR-1000 1-bit digital recorder, Amanero Combo384 DSD output adapter and the discontinued exaU2I USB to I²S interface.
Software supporting DSD includes Sonic Studio's Amarra Luxe, Audirvana, foobar2000 with SACD plugin, JRiver Media Center, Roon, HQPlayer and Neutron Music Player are all able to handle DSD files of up to DSD512 rate fully natively.