Originally posted by mrs peacock
Can someone inform me what SACD is?
Thanks
it's a new digital format being introduced by sony/phillips that captures audio in a totally different way.
it's still on a CD, but working on a different principle.
there are some dual layer SACDs being released now that can be played as normal CDs as well, which is a smart way to introduce the format.
i've yet to hear one, but from what i've been told by people who have, it will erase the arguements for analogue mediums.
CDs were never as good as they said they would be, and raising the sampling rates and bit depths were never going to fix all the limitations.
now that i've read a bit about it, it freaks me out how cool this is.
for those interested in the science, here's a bit of cut and paste:
technical
DIRECT STREAM DIGITAL™ (DSD™) ENCODING
Sony and Philips both have a well-known history of accomplishment in Pulse Code Modulation (PCM) digitalaudio. Starting in the late 1970’s with commercial 14-bit systems, and moving up to 16-, 18-, 20- and 24-bit systems, these two companies have made an unmatched investment in PCM technology, generating an unequaled string of PCM products. So it’s not casually that these two companies now propose a fundamental move away from PCM.
Successively higher bit rates and higher sampling rates for PCM systems have, in fact, improved sound quality. But the improvements are getting smaller and smaller. And the reason for these diminishing returns is becoming clear: filtering. Every PCM system requires steep filters at the input to absolutely block any signal at or above half the sampling frequency. (In conventional 44.1 kHz sampling, “brick wall” filters must pass 20 kHz audio, yet reject 22.05 kHz — a difficult task.) In addition, re-quantization noise is added by the multi-stage or “cascaded” decimation (downsampling) digital filters used in recording and the multi-stage interpolation (oversampling) digital filters used in playback.
This problem was the inspiration for Direct Stream Digital. By simply eliminating decimation and interpolation in existing processes — we developed a whole new way of capturing audio signal digitally. As in conventional PCM systems, the analog signal is firstconverted to digital by 64x oversampling delta-sigma modulation. The result is a 1-bit digital audio signal. Where conventional systems immediately decimate the 1-bit signal into a PCM code, Direct Stream Digital records the 1-bit pulses directly.
The delta-sigma analog-to-digital converter basically consists of integrator, 1bit quantizer and negative feedback loop path. The amplitude of the input analog signal is represented by the density of pulses output. The density of output pulses increases with increasing input signal amplitude.
Meanwhile digital-to-analog conversion can be as simple as running the pulse train through an analog low-pass filter!
Ultra-high signal-to-noise ratios as required for DSD in the audio band are typically achieved through 5th-order delta-sigma modulator. These effectively shift the noise up in frequency, out of the audio band: noise shaping.
Sony and Philips designed DSD to capture the complete information of today’s best analog systems. The best 30ips half-inch analog recorders can capture frequencies past 50 kHz. DSD can represent this with a frequency response from DC to 100 kHz. To cover the dynamic range of a good analog mixing console, the residual noise power was held at -120 dB through the audio band.
A simplified relationship between analog input (above) and 1 bit digital output pulse train (below) of the delta-sigma analog-to-digital converter (The pulse train has been shaded for clarity.)
A simplified illustration of the effect of noise shaping. The maximum audio frequency, fm, is nominally 20,000 Hz. Noise shaping moves most of the noise power far above the audio band (20kHz-), where it will be inaudible.
A notorious torture-test for recording systems, the 10 kHz square wave (top trace) includes component frequencies well above the audio band. The 16-bit PCM system approximates this with a 10 kHz sine wave (left figure: top trace). In comparison, the 1-bit Direct Stream Digital captures the wave's true shape (right figure: bottom trace).
