Super Audio CD

Super Audio CD (SACD) is a type of optical disc jointly developed by Philips and Sony, released in 1999 and designed to provide high-definition audio.

Overview

SACD can be considered a hybrid between the CD and DVD formats. That is, it is a compact disc format that uses the same sector size, error correction system, modulation and file system (UDF and ISO 9660) as a DVD. Although it uses DVD technology, the SACD cannot be played on all DVD players (in any of its types: universal, video, audio), since it does not use the same type of audio coding as the DVD disc, however, it can be compatible with some models.

Due to its relationship with the DVD, although the SACD is a format designed only for audio, it allows an area within the disc to be reserved for other data and allows the inclusion of video clips, text, graphics, etc.

SACD uses a digital audio coding system called Direct Stream Digital (DSD), developed by Sony.

The frequency response of the SACD reaches 100 kHz, well above 20 kHz (the frequency considered the limit of human hearing). However, it is necessary to keep in mind that this technology does not keep the quantization noise constant throughout its range, that is, the signal to quantization noise ratio (SNQR) since it deteriorates significantly above the audio frequency band. The critical frequency of the audio CD is 22.05 kHz (also above the aforementioned limit), although the analog filters of the players progressively attenuate audio signals above 20 kHz. In any case, the ultrasonic potential of a digital audio format is a very debatable characteristic at best and for obvious reasons. Likewise, the existence of signals with ultrasonic components could generate distortion due to intermodulation in normal audio frequency amplifiers. On the other hand, the SACD format provides an extensive dynamic range, in the audio frequency band, of 120 dB, which exceeds 98.01 dB of the CD.

A single-layer SACD format disc has a greater storage capacity (4.7 GB) compared to a CD (700 MB). This is possible thanks to the fact that the width of the courts has been reduced, the size of the holes or "pits" (recording marks on the surface of the disc) and the type of lossless compression technology (DSD) uses. This great capacity allows the SACD to offer 6 audio channels of identical quality.

There are three types of SACD according to the layers that constitute it:

• 1 layer, with stereo audio information.
• 2 layers, with stereo and multichannel audio.
• 3 layers, stereo audio, multichannel audio and conventional CD audio.

Each layer is read by a laser beam with a different wavelength (the longer the wavelength, the greater the depth, so the lower layers can be read). The information in each layer is invisible to the laser of the other format player, ensuring compatibility.

The three-layer SACDs that allow compatibility with the CD are called hybrid SACDs. The problem is that manufacturing hybrid discs is more expensive and complicated than manufacturing discs only for Super Audio CD, but this increase in production costs is compensated because the market share expands exponentially.

Sony and Philips, being the designers of the format, are the main manufacturers of players, both conventionally and combined with DVD players. The PlayStation 3 video game console also allows multichannel SACD^{[citation needed]} playback, even through the optical output. Only the Playstation 3 version 60GB console is capable of playing SACD.

A hybrid SACD disc can be read by a conventional CD player, but CD players cannot decode the information on SACDs.

To avoid so-called record piracy, an anti-copy system known as Pit Signal Processing is incorporated into the manufacture of SACDs, which records 2 “watermarks”:

1. An invisible brand that is recorded in the data plot itself.
2. Another visible mark, which is on the surface of the disk and masks the actual size of the holes or pits to form an image that should be “impossible” to copy. At least, there is still no known method to do so.

Audible differences compared to CD-Audio and DVD-Audio

Experimental works have been published that have been assumed to be rigorous that conclude that there are no audible differences between the SACD format and the traditional digital audio support Audio CD (PCM 16 bits; 44100 samples/s). These tests refer only to stereo musical material since the Audio CD does not allow recording multichannel sound material. Other studies, such as that carried out by experts from the Detmold University of Music in Germany, Dominik Blech and Min-Chi Yang, have proven that the sound quality of SACD is indistinguishable from the high-resolution DVD-Audio format.

For American audio engineer Thomas Kite, any statement about the audible virtues of these "high definition" Regarding the Audio CD, they are only audiophile myths or marketing messages that seek to promote the new production of recordings or players with statements that are never supported by rigorous statistical tests, double-blind methodology, with significant samples and, above all, independent.