Direct Stream Digital (DSD); Digital eXtreme Definition (DXD) and Hi-Res AUDIO

Direct Stream Digital (DSD)

Translatable from English as direct digital stream, is a trademark registered by Philips and Sony for a system for decoding audio signals using Pulse-Density Modulation coding, a technology used to store sound signals on digital media such as Super Audio CD (SACD).

Technique
The audio signal is translated through Sigma-Delta modulation, as a sequence of single bits at a sampling frequency of 2.8224 MHz (64 times the sampling frequency of an Audio CD, equal to 44.1 kHz). Using a higher sample rate allows for noise shaping (a technique used to minimize the quantization error of audio signals by spreading it over a wider range of frequencies) to reduce the noise and distortion caused by the quantization of a single-bit audio signal. On the other hand, it is still a matter of debate how much distortion can be eliminated in a 1-bit sigma-delta conversion..

 

It is a digital audio format, originally developed for editing high-resolution DSD recordings, audio standards used in the Super Audio CD (SACD) format.

Technique
Since the 1-bit DSD format used on SACD is not suitable for editing, other formats such as DXD or DSD-Wide must be used during the mastering stage. Unlike DSD-Wide or DSD which offers good editing, equalization and cross-fade possibilities at the DSD sampling frequency (64 frames, 2.822 MHz), the DXD format is a PCM modulated signal with a resolution of 24 bits (8 bits more than the 16 bits used for the Red Book CD) sampled at 352.8 kHz - eight times the 44.1 kHz sampling rate of the Red Book CD. Data throughput is 8.4672 Mbit/s per channel, three times that of DSD64. DXD also uses a wide range of plugins available for PCM-based digital audio workstations, such as Cubase, Logic Studio, Digital Performer, etc. DXD was initially developed for the Merging workstation Pyramix and introduced with their Sphynx 2 analog-to-digital converter in 2004. This combination meant that it was possible to record and edit directly in DXD and that the sample was only converted to DSD once, before of the publication in SACD. This offers a huge benefit to the user, as the quantization and compression noise generated by DSD conversion increases significantly above 20kHz and more noise is generated each time a signal is converted to DSD during editing. Currently, DXD is also used as a music distribution format.

Hi-Res AUDIO

In 2014, the Digital Entertainment Group, Consumer Electronics Association and The Recording Academy, along with record companies, defined the concept of high-resolution audio (Hi-Res AUDIO) as "uncompressed or lossless compressed audio (LOSSLESS ) of higher quality than normal CD standard ". In other words, we refer to a digital audio content and the possibility of being reproduced with a sampling frequency and/or a bit depth greater than 44.1 kHz and/or 16bit.