Super Audio CD - Part 1: SACD Overview
High Definition Audio Formats for Music Listening
The Super Audio CD - or SACD for short, is one of those high definition multi-channel audio formats designed specifically for music listening. In the first part of this article, we discuss the Super Audio compact disc, audio specifications, format variations and the Hybrid disc.
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Super Audio CD: Introduction
A High Resolution Audio CD with a Difference!
The Super Audio Compact Disc was originally developed by Sony and Philips Electronics in 1999, the same companies that created the CD. It is a read-only optical audio disc designed to provide a much higher audio quality than that supported by the CD-Digital Audio format.
The SACD audio disc supports high-resolution sound in either two-channel stereo or multi-channel audio, with up to six full-range discrete channels of music. It also supports storage capacity for text, images, copyright protection, and more in a similar manner to its DVD-Audio counterpart. However, unlike DVD-A, the Super Audio CD does not use PCM. Instead, it is based on what is called Digital Stream Direct (DSD).
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A fundamentally different technology...
Direct Stream Digital (DSD) is fundamentally different from PCM. But it is thanks to this DSD encoding technology that SACD audio is capable of delivering improved frequency response and extended dynamic range that leads to a more analog-like performance in terms of music reproduction, than that possible with CD Audio.
Yet, like its DVD-Audio competitor, the Super Audio CD has still a long way to go to acquire the desired level of consumer acceptance. Rather, in 2009, Stereophile magazine stated that audiophiles consider SACD dead. Still, the Super Audio CD is still around even though it is estimated that sales of both DVD-A and Super Audio CD discs amounts to less significantly less than 2% of all physical media content such as sales of DVDs, CDs and digital downloads.
Worst still is the fact that these new high resolution audio formats have come at a time when all forms of physical media content - whether it is music or video, are experiencing a negative trend in sales as against the present explosive growth in digital downloads.
To make things worse, the format war between the Super Audio CD and DVD-Audio, especially during the first years of their existence, left many end-customers somewhat uncomfortable to jump onto the bandwagon of high-resolution audio.
Today, this format war is no longer an issue to music lovers and audiophiles. Good quality universal DVD players capable of handling both DVD-Audio and SACD, are available at just over $100. A suitable option within this price bracket is the Pioneer DV 610AV-K even though a premium quality universal disc player such as the OPPO BDP-103 Universal Disc Player featured above sells for around $500.
In addition, the fact that Super Audio CDs and DVD-Audio discs are being priced at CD levels is leading to a situation where choice is driven solely by music content rather than audio format - which is what should be the case.
Furthermore, the present shift towards hybrid discs - featuring a CD layer for backward compatibility with standard CD players, is surely making it much easier for end-customers to shift their choice towards these high-resolution audio discs.
This means that even if most customers do not yet possess the necessary audio playback setup to get the very best out of these high-definition audio formats, they still have the possibility to start building their high resolution audio disc collection, while enjoying standard CD audio till they decide to upgrade their audio gear.
The Super Audio CD disc itself looks like an ordinary audio CD or DVD disc. Yet the basic super audio CD disc is closer to a DVD in terms of physical characteristics and data capacity. The table below compares the Super Audio CD disc with an Audio CD.
|Specification||Super Audio CD||CD-DA|
|Audio Format||Direct Stream Digital||Linear PCM|
Note: GB is the metric equivalent while GiB is the binary equivalent.
4.70GB/4.38GiB - Single Layer [DVD-5]
8.54GB/7.95GiB - Dual Layer [DVD-9]
|Read Mechanism||650nm semiconductor laser||780nm semiconductor laser|
|Channels||Up to 5.1||2 (stereo)|
|Frequency Response||0 - 100kHz (max)||5 - 20kHz|
|Dynamic Range||120db max. within the audible range (0 - 20kHz).||96db|
|Sampling Rate - 2 channel||2,822,400 samples per second.||44,100 samples per second|
|Sample Resolution (Quantization)||1 bit||16 bits|
|Maximum Data Bit Rate (for 2-channel audio)||5.64 Mbps||1.4Mbps|
|Developed by:||Sony and Philips||Sony and Philips|
There are three types of Super Audio CD Discs:
Single-layer Super Audio CD: Physically, this is a DVD-5 DVD with a 4.7GB high density layer only for stereo and/or multi-channel DSD recording - capable of delivering up to 100 minutes of high resolution stereo or 80 minutes of multi-channel + stereo sound.
Dual-layer Super Audio CD: Physically, a DVD-9 DVD with two high-density layers for a total of 8.54GB capacity - thus enabling longer playing times of either 2-channel or multi-channel DSD recording.
Hybrid Super Audio CD: This is the most popular of the three. The hybrid disc is somewhat similar to the dual-layer disc in terms of concept, in that it contains a high-density SACD layer and an audio CD layer physically bonded on the same disc. This makes the disc looks like a regular audio CD disc to a CD player or CD-ROM drive.
The Hybrid Super Audio CD and Backward Compatibility
While the single or dual layer Super Audio CD discs are not backward compatible with CD players, yet the presence of a CD-layer in a Hybrid SACD disc renders the latter playable on any of the hundreds of millions of CD playback equipment available worldwide.
SACD Disc: Signal Reading Process
The Hybrid Super Audio CD process is possible because the high density layer - while acting as a reflective surface to the shorter wavelength SACD laser - is penetrated by the 780nm laser rays used by CD-DA. Furthermore, the objective lenses used by the CD-DA and Super Audio CD lasers focus the laser rays at different distances (1.2mm and 0.6mm respectively), in accordance with the different layer depths. (Ref. to diagram).
Thus, when the hybrid disc is placed in an SA-CD player, the laser is reflected by the high-resolution layer (at 600 µm distance) before it can reach the conventional layer. Similarly, if a conventional CD is placed into an SACD player, the laser will read the disc without difficulty since there is no high-resolution layer.
Hybrid discs are always marked as either 'Hybrid SACD' or as 'compatible with all CD players'.
As already indicated, Super Audio CD discs may come in stereo and/or multi-channel audio. In all, there are four main variations of the Super Audio CD.
Discs with this emblem will only play in Super Audio CD players.
These discs play in all standard CD players, as well as Super Audio CD players.
Multi-channel can include anything from 3 to 5.1 channels of audio. Each multi-channel disc also includes a separate two-channel version of the music for complete compatibility with two-channel Super Audio CD players.
These discs will only play in Super Audio CD players, providing stereo sound on two-channel players and multi-channel sound on multi-channel players.
Discs with this graphic will play stereo sound in all CD players, as well as stereo and/or multi-channel high resolution sound in compatible Super Audio CD players.
It is interesting to note that whereas most multi-channel audio sources would resort to computerized 'fold-down' of the channels for playback on stereo systems, this is not the case with SACD audio.
Each multi-channel Super Audio CD actually contains both the multi-channel program and a separate two-channel version right from the hands of the producer. In other words, rather than a computerized approximation, you always get exactly what the original artists intended.
Recording Areas on a Super Audio CD Layer
Next: Direct Stream Digital