What is SACD?

In my article on Digital to Analogue Convertors I briefly covered how music is captured digitally. Compact discs use the redbook standard, which captures the music produced in 16 bit words, and takes samples 44,100 times a second. This was pretty impressive for 1980, when the standard was published.

However, 19 years later, it was felt that technology and understanding had advanced, and that a better standard could be developed. Two standards competed - DVD Audio, and SACD. I'm not going to talk about DVD Audio, instead focusing on SACD.

How does SACD work?

Unlike the way I described in the DAC article, where (in my simple example) we used three bits and a divide and query approach to sample the analogue wave form, SACD uses a different approach, called DSD (Direct Stream Digital). This uses a 1 bit word - ie it only stores two possible states (versus 65,536 for a 16 bit word used by CD). The data it stores is whether the amplitude of the signal is greater or lesser than the previous one. The number of samples taken is much greater - 64 times greater, in fact.

The advantage of this is that much much less processing is needed to get an audible signal, which means less filtering, and less chance for noise to creep in.

Is SACD better than CD?

For its time, CD was a remarkable format, and still delivers exceptional sound. However, technically speaking, yes, SACD is a better format.

Technology had advanced by 1999, such that much more data could be stored on a disk. It also made it possible to record more than two channels of music - a prospect potentially very appealing to some listeners.

Because of the frequency of samples, CD has a cut off point at around 20kHz - sounds above that frequency are thrown away. SACD captures and replays sounds up to 100kHZ.

The dynamic range of CD - that is the difference between quiet and loud - is about 90dB. SACD is 120dB. This means that recordings can be quieter, and the difference between loud and quiet passages can be more pronounced. In large scale classical music, for example, this could be significant.

Aside from the pure technological advantages, there's another interesting, although anecdotal improvement, that I've experienced.

A common complaint made by those who preferred records to CDs was that CDs just didn't quite get the timing right. This is hard to explain, but easy to feel. It's easier to get a strong stereo image with a record versus a CD player, and on certain kinds of music where the rhythm is subtly swung, CD can just sound a bit regimented. I've certainly found this to be the case. Music on SACD seems not to suffer from this timing issue.

Can we even hear about 20kHz?

A common complaint made by those with a little technical knowledge is that the human ear cannot hear above about 20kHz, so it's really no problem to throw away frequencies above this threshold. It's an argument repeated to this day by people like Sonos, who resolutely insist that there's no point in streaming so-called Hi-Res music, when the CD sample rate was specifically designed with the limitations of the human ear in mind. It is, frankly, good enough.

It's true that the human ear has a limitation with respect to the frequencies it can hear. This is indeed around about 20kHz. However, this misses two very important points.

Firstly, just because the ear cannot hear above 20Khz, doesn't mean there's nothing there. Indeed, a study by California Institute of Technology showed that at least one member of each instrument family (strings, woodwinds, brass and percussion) produces energy to 40 kHz or above, and the spectra of some instruments reach this work's measurement limit of 102.4 kHz.

Amazingly, the percentage of energy above 20 kHz was 2% for a trumpet, and a staggering 40% for cymbals.

This is musical information which is available to the listener in a live performance, which, given that it's possible, should, arguably, be made available to the listener in the home.

Secondly, an important study in the Journal of Neurophysiology demonstrated that listeners who were played the same music, sometimes with frequencies above 25kHz and sometimes without, consistently showed additional alpha-wave activity. Even if they couldn't hear it, they could clearly perceive it. The same test also showed that they preferred the music with the ultrasonic frequencies included.

While the findings regarding preference have been disputed, nobody has challenged the physiological response. Clearly our bodies and brains respond to these frequencies, in a way we don't understand.

Is SACD a dead format?

SACD is demonstrably a superior format, in a number of ways, and there is scientific and experiential evidence to support this. However, isn't this a bit moot? History is full of theoretically better implementations that simply didn't work. SACD failed, right?

Actually, not right.

At present, there are nearly 11,000 titles available. 66% of these are classical, and 13% of them are jazz. New titles are released regularly. Scan the reviews of Gramophone each month, and you'll see new recordings of new pieces, or new interpretations each month.

Yes, it's a niche, but in that niche, it's alive and well.

As I'm a particular fan of classical music, and especially follow modern classical music, and the growing interest in formerly unfashionable 20th century English classical music, this is relevant, and exciting for me.

Interestingly, the fact its a niche, could also help explain why SACD generally does sound better than CD. It's a small, elite, specialist corner of the music industry, where volume sales don't matter so much. It's understood that those who do listen to SACD are likely to be discerning listeners, and quite possibly have very high quality equipment. As such, the mastering could well be considerably better.

How do I listen to SACD?

Suppose you, like me, are convinced by the technology. Suppose you also take a pragmatic approach to science - it's only as good as our current understanding. The fact we don't understand something doesn't mean it isn't there, or it isn't real. I can hear, feel, sense, and experience a qualitative difference when I listen to SACD, and the science backs me up.

Suppose you're also primarily interested in classical and jazz music, and would like to take advantage of these excellent recordings, and bask in the glorious sound that is available.

How do you get involved?

Well, it's simple. You just need a disk player that supports SACD. These are, obviously, not as common as CD players, but can be had for a reasonable price. We offer one at £380, which is primarily designed for Blu-Ray disks. A better quality, dedicated CD/SACD player will set you back about £1000.

Personally, I use a Primare BD32, which brings me tremendous delight.

Then all you need is to connect it to your amplifier and speakers, and away you go.

Of course, if you want to explore the world of multichannel audio, you'll need more channels of amplification, and more speakers. If that sounds interesting, get in touch, and we can help you there too.