Super Audio CD

The Super Audio CD was launched officially by Philips and Sony in September 1999. It is about a support of music, as well as the CD: the support of wafer in Polycarbonate 12 cm in diameter of audio CD was preserved, storage capacity being widened (of 700 Mo with 4,7 Go).

Concerned on good information of the public in the cultural field which is theirs, and in order to avoid any risk of confusion, the Sony companies decided, in agreement with the Société of the Authors and Dramatic Type-setters (SACD), which the format Super Audio CD exploited by Sony is not indicated any more by initials “SACD”, but by the Super terms Audio CD.

Description

The Super Audio CD uses a technology of digitalization DSD ( Direct Stream DIGITAL ) to very high Sampling rate (2,8244 MHz) quantified on 1 bit which authorizes a Band-width going up to 80 Khz even 100 Khz and a dynamics of 120 dB; it is quite higher than that recommended by the theorem of sampling of Nyquist-Shannon: it is worth 64 times the sampling rate of the CD audio. This process ensures a better coherence of the phase of the signal than the process PCM (Pulse Coded Modulation) used for the more current audionumerical formats (Compact Disc, DAT, files of the Wav type or AIFF, etc). Analog-to-digital and digital-analog conversions are also simplified, ensuring a better quality of conversion of the signal for less production costs. It in addition allows a spatialization in addition to stereophony two channels used up to now. To increase the capacity of recording of the Super Audio CD audionumerical flow undergoes a compression without loss called DST (Direct Stream Transfer) authorizing up to 80 minutes of recording of stereo tracks DSD and multichannel DSD.

The Super Audio CD, in spite of its coding on 1bit, has a resolution equivalent (after filtering) to that of DVD Audio (24 bits). The techniques put in plays for this purpose refer to the “ Noise Shaping ” or formatted of the noise of quantification by which this last is pushed back towards frequencies apart from the useful zone. This modulation 1 bit (all or nothing) is not new, it are connected with the modulation of width of impulses (or PWM Pulse Width Modulation used in the inverters, amplifiers of class D, devices with valve of light: microphone-mirrors DMD, etc) for which the cyclic report/ratio varies according to the amplitude of the signal to transcribe. Numerical flow 1bit (DSD) must however follow a rate/rhythm of clock imposed (which corresponds to the oversampled frequency) one speaks then about PDM (pulsates density Modulation) or modulation of density of impulses. All turntables HALF-VALUE LAYER and DVD-A profit from a modulator “a bit” making it possible to find, starting from a flow PCM (16, 20 or 24 bits), a flow of the type DSD (1bit) which is very simple to convert into analogical (low-pass filtering of a nature relatively low). The digital processing associated with this modulator (delta-sigma) is then avoided during the reading of flow DSD of the Super Audio CD.

Types of formats

There exist two possible formats:
  • the simple disc lays down HD (high density): it includes/understands a stereo mixing and/or a multichannel mixing (4,5 or 6 channels) only readable on a reader Super Audio CD;
  • the hybrid disc double-layer: the format Super Audio CD hybrid, the first with being distributed, contains two layers: the first (deepest) perhaps read on a turntable standard CD; it contains a stereo audionumerical signal coded in LPCM ( Linear Pulse Coded Modulation or modulation of linearly coded impulses). The second layer of high density (standard DVD) can accommodate a multichannel audionumerical flow of type DSD and auxiliary data (texts, images, etc); it is transparent for the beams laser wavelength 780 Nm. The layer multichannel is not systematic.

Commercial aspects

Because of the Net progress of quality compared to audio CD (less intermodulation of phase, precision in the acute ones, Harmonic richness of the S, comfort of listening, etc) the Super Audio CD allows, with the help of a renewal of equipment limited in a good chain stereophonic Hi-Fi (specific platinum of reading also reading audio CD), to find the sound of the old vinyls, with a better dynamics and without background noises.

By the possibility that it gives of “its space” (multichannel), the Super Audio CD allows to the editors sound records to completely republish their catalog near the amateurs. Artists like the Beatles or the Rolling Stones indeed always worked, in studio, on tapes with 8,16,32 and sometimes even 64 tracks, and it is thus very easy to republish them into multichannel, transforming into market of equipment market which was hitherto only of renewal. The Classical music, especially symphonic, also can in this way touch all a new category of listeners. Lastly, which is not negligible, the market of the disc does not have any more a risk to only suffer from the diffusion radio phonic of works, as long as the radio operator remainder limited to the Stéréophonie.

However, the force of the Super Audio CD is also its weakness, because it implies a renewal of the material to profit from the multichannel sound, making more expensive it thus than for simple stereophony. Moreover, to profit fully from the “space sound”, a “pointed” installation of the material is necessary, when one radically should not modify the overflow room. For all these reasons, the Super Audio CD seemed limited to a niche market until the advertisement of its integration in the console general public PlayStation 3.

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