SACD-CD Hybrids -- A Way Out For Us Both?

net_shaman writes: "As reported in Stereophile Magazine online -- There appear to be some serious moves afoot by the recording industry to move en-mass to another compact audio disc format. No doubt frustrated with the utter failure of every attempt to copy protect Compact Discs. But this could be an opportunity for both better sound, strong copyright security and reasonable fair-use rights. The Hybrid Super Audio Compact Disc contains two layers of encoded information; one for standard 'Red Book' Compact Disc, and another for high resolution audio recordings (SACD). Here is a description."

"An interesting feature of the SACD layer is plenty of room for strong digital rights management code.

Here's my proposal: it should should allow artists to get paid, and the citizens to have archived and portable copies of the recording they have purchased. The record companies should produce a superior audio product and get to protect it from serial copying. The CD layer should be freely available for personal copying such as to a computer or portable digital player. These 2 basic concepts are a model that can be applied in the future, when better formats become available. It may also serve as a model for digital visual recordings. Perhaps we can get the artists, publishing companies, electronics manufacturers and the federal trade commision to all agree on this compromise: 1.The high quality recording allows only one copy of itself to be made for archival purposes. 2.The lower quality recordings are available for personal copying.

Personal digital technology has brought a tremendous change to the realtionship between media publishers & consumers. It's time for a new paridigm that will re-define that relationship for modern times."

Comments

The Three Types of the SACD Disc

[Anonymous Coward]

The SACD standard, published by Philips and Sony in March 1999, defines three possible disc types (shown above). The first two types are discs containing only DSD data; the single layer disc can contain 4.7 GB of data, while the dual layer disc contains slightly less than 9 GB. The third version - the SACD Hybrid - cleverly combines a single 4.7 GB layer with a conventional CD that can be played back on over 700 million cd player world wide. This concept is the essential link between the new SACD format and the well-established CD.

From the outside, the SACD Hybrid Disc looks like any other 12 cm diameter and 1.2 mm thick optical disc. A closer look reveals that the disc is a bonded combination of two 0.6 mm data carriers: one containing the SACD data, the other the CD data. The reflective coating on the SACD carrier has the optical characteristic to be reflective for the light used in the SACD pick-up (650 nm), but to be transparent for the light used in a CD pick-up (780 nm). To a CD pick-up, the SACD layer is virtually invisible, as a result, the CD layer contained within the SACD Hybrid Disc is fully compatible with the "Red Book" CD standard, and can, therefore, be played on all "Red Book" compliant players.

Personal Experiences With SACD

[cporter]

I have a Sony SACD player and a fairly good system to listen to it on - but much less than the "$10,000" mentioned by a poster above. I have some 30 discs that i've paid $12.99 - $22.99 for. The sound is phenomenal. Anyone who has sat for a listen agrees. It is better than CD, even though the recording and mastering of CDs has gotten much, much better over the last few years.

The great truth of recorded music is: The life and death of any format is in the software, not the players, not the technology, not the marketing. How much music is there? The biggest problem SACD has is that there's less than, oh about 400 discs available, mostly classical and jazz, and mostly older recordings, at that. One great advantage for SACD is that Sony has begun all mastering in DSD, the one-bit technology behind SACD. That recently-released CD you bought from a Sony label was probably recorded using DSD and downsampled for the CD master.

MP3 and other compressed formats have lots of software available.

One other note: I have a two channel system (i.e., Stereo) but SACD supports a 5.1 channel layer, too. So a fully-loaded hybrid SACD has a 2-channel Red book CD layer, a 2 channel SACD layer, and a 5.1 channel SACD layer. Only the 2 channel SACD is required.

Analog waves

[wirelessbuzzers]

The SACD uses a different sampling technique from a CD. Both of them stare with a sigma delta modulator, which breaks the analog signal from the mic into a series of pulses, the denser the pulses the higher the amplitude. A normal recording counts the pulses over about 45 microseconds (for 44.1 kHz) to get a 16-or 24-bit wide number IIRC. when the music is played back, it is converted back to 1-bit by, say, varying the duty cycle of a pulse-width modulator.

The SACD just records the pulses from the SD modulator to disc, which is responsible for the huge number of samples.

So instead of being 44.1 kHz*16 or 24 bits per sample, it is 1.2 MHz at one bit per sample. Therefore, it looks *less* like an analog wave than a CD recording. Essentially, Sony regards counting the pulses as a very effective but slightly lossy compression method that they wish to eschew. BTW I can barely tell the difference. Even a good MP3 is good enough for me.

I have SACD, too.

[HardCase]

sorry, but unless they have mixers, microphones, and other equipment that is before the encoder (and the encoder it's self) that will pick up and handle above 44Khz (Note: they DON'T) it's worthless. Let alone the fact that your speakers CANT reproduce anything above 30Khz equals abilities that mean nothing and offer nothing...

Anyone can polish a turd... and SACD is a turd polisher.

I'm not sure what you mean by "above 44Khz". The absolute limit of CD audio is 22KHz as shown by the sampling theorem that basically states that the sampling rate must be a minimum of twice the maximum frequency sampled. Besides, the goal of high fidelity audio is the faithful reproduction of the original sound. In the frequency domain, that translates into flat response between 20Hz and 20KHz with a smooth rolloff above and below. CD audio does not do that.

A huge problem that plagues CD audio (from the audiophile point of view) is the "brick wall" filter that is employed at 20KHz. This low pass filter is so sharp that it can cause some pretty nasty artifacts if it's implemented improperly (for which you should read "cheaply").

Your point about "mixers, microphones, and other equipment" would be well taken except that Sony's Direct Stream Digital (DSD) recording system doesn't allow for post-recording mixing at all. So, what you record is what you get. Obviously, then, the quality of the recording stream should be correspondingly high. I think that you'd be quite surprised at just how high the standards for DSD recording equipment are.

A significant advantage of SACD over CD is that because of the 1 bit sampling and the dithering that follows, quantization noise is moved way up in the spectrum, well beyond the range of audibility. Further, the noise floor of SACD is substantially lower than that of 16 bit CD. The frustrating part of CD audio is that although it should provide a theoretical 16 bit dynamic range, due to quantization and other digital artifacts, even the best players are limited to perhaps 12 or 13 bits. Sure, you might dismiss that as a mere detail, but it is quite audible.

I've got a Sony SACD player. I've also got a nice Rega turntable and a Musical Fidelity CD player. A well cared for LP certainly outperforms a CD and is on a par with the SACD player. Obviously it's difficult to keep an LP in excellent condition over time, which is why I have a very large CD collection. But, quite frankly, the 30 or so SACDs that I have most definitely sound better than the CDs that they replaced...and I'm no golden-eared audiophile.

I'll certainly agree that my speakers won't reproduce anything above 30KHz, but that's not the point of SACD. The point is that the dynamic range is substantially greater and the digital artifacts that are the domain of multibit sampling (and relatively low sampling rates) are essentially eliminated. Frequency response is not the issue here.

I suppose that the case of SACD being a "turd polisher" could be made if you wanted to stick one in your average boom box and claim superior sound. But then again, I guess you could say that in that regard, CD is just a turd polisher compared to cassettes.

-h-

Re:I have SACD, too.

[cjs]

A huge problem that plagues CD audio (from the audiophile point of view) is the "brick wall" filter that is employed at 20KHz. This low pass filter is so sharp that it can cause some pretty nasty artifacts if it's implemented improperly (for which you should read "cheaply").

This has not been a problem for years. You just interpolate the signal up to a nice high sampling rate (say, 264.6 KHz), use a digital filter that gives you a very sharp slope and no phase shift, and then at the analogue output stage you can use a very gently sloping analogue filter with minimal phase shift to get rid of the remaining very high harmonics.

cjs