So what exactly is BluRay, CD, DMM, DSD SACD and XRCD?
SACD audio is stored in a format called Direct Stream Digital (DSD), which differs from the conventional Pulse-code modulation (PCM) used by the compact disc or conventional computer audio systems.
DSD is 1-bit, has a sampling rate of 2.8224 MHz, and makes use of noise shaping quantization techniques in order to push 1-bit quantization noise up to inaudible ultrasonic frequencies. This gives the format a greater dynamic range and wider frequency response than the CD. The SACD format is capable of delivering a dynamic range of 120 dB from 20 Hz to 20 kHz and an extended frequency response up to 100 kHz, although most currently available players list an upper limit of 70–90 kHz, and practical limits reduce this to 50 kHz. Because of the nature of sigma-delta converters, one cannot make a direct technical comparison between DSD and PCM. DSD's frequency response can be as high as 100 kHz, but frequencies that high compete with high levels of ultrasonic quantization noise. With appropriate low-pass filtering, a frequency response of 50 kHz can be achieved along with a dynamic range of 120 dB. This is about the same resolution as PCM audio with a bit depth of 20 bits and a sampling frequency of 96 kHz. Thus, DSD looks inferior to a "standard" PCM 24bit/96 kHz even using slightly more bandwidth than PCM (2.8224 Mbit/s vs 2.304 Mbit/s).
In the audiophile community, the sound from the SACD format is thought to be significantly better compared to older format Red Book CD recordings. However, In September 2007, the Audio Engineering Society published the results of a year-long trial in which a range of subjects including professional recording engineers were asked to discern the difference between SACD and compact disc audio (44.1 kHz/16 bit) under double blind test conditions. Out of 554 trials, there were 276 correct answers, a 49.8% success rate corresponding almost exactly to the 50% that would have been expected by chance guessing alone. The authors suggested that different mixes for the two formats might be causing perceived differences, and commented:
Now, it is very difficult to use negative results to prove the inaudibility of any given phenomenon or process. There is always the remote possibility that a different system or more finely attuned pair of ears would reveal a difference. But we have gathered enough data, using sufficiently varied and capable systems and listeners, to state that the burden of proof has now shifted. Further claims that careful 16/44.1 encoding audibly degrades high resolution signals must be supported by properly controlled double-blind tests.
This conclusion is contentious among a large segment of audio engineers who work with high resolution material and many within the audiophile community. Some have questioned the basic methodology and the equipment used in the AES study.
Double-blind listening tests in 2004 between DSD and 24-bit, 176.4 kHz PCM recordings reported that among test subjects no significant differences could be heard. DSD advocates and equipment manufacturers continue to assert an improvement in sound quality above PCM 24-bit 176.4 kHz. Despite both formats' extended frequency responses, it has been shown people cannot distinguish audio with information above 21 kHz from audio without such high-frequency content.
To reduce the space and bandwidth requirements of Direct Stream Digital (DSD), a lossless data compression method called Direct Stream Transfer (DST) is used. DST compression is compulsory for multi-channel regions and optional for stereo regions. This typically compresses by a factor of between two and three, allowing a disc to contain 80 minutes of both 2-channel and 5.1-channel sound.