Term Definitions

SACD stands for Super Audio Compact Disc; they are high resolution optical discs developed jointly by Sony and Philips which first became widely available in 1982. The SACD medium supersedes by far the fidelity, storage capacity, dynamic range and stereo imaging capabilities of the standard CD. Its original source may any analog or digital master, but best quality is usually from an audio stream recorded with the Direct Stream Digital (DSD) process, which is also used for the mastering of the distributed SACDs. It is a 1-bit system using a 2.8224 MHz sampling rate, and a dynamic range of 120 dB and frequency range of 20 Hz to 50 kHz. Each SACD can store up to nearly 8 GB of data, and includes both stereo and multichannel DSD options as well as a standard Red Book 44.1K/16-bit CD layer for compatibility with any CD player.

Well over 6000 SACD releases have been published so far, with more than half being European classical music. Jazz and pop SACDs have been mostly remastered versions of previous albums originally recorded on tape. Despite the global decline of CD sales, the sales of SACDs and players increased in 2010. Many inexpensive players are now available which play SACDs as well as CDs, DVDs, and even Blu-ray discs.


Blu-ray discs supersede standard DVDs in terms of resolution, storage capacity, and the fidelity of their soundtracks. Just as DVDs were a major step forward in better image and sound of movies and music videos, Blu-rays offer a huge enhancement over standard DVDs, and many studios put a great deal of effort into digital restoration of the original film images and sound for Blu-ray release, as well as a single disc have plenty of storage space for many different bonus features plus lossless surround soundtracks.

The physical disc is the same 5″ side as DVDs, SACDs and CDs, and contains 25 GB per layer, with most discs having two layers. Its official release was in 2006 and more than 3,300 titles have been released so far. A blue laser reads the smaller pits on the disc, hence the name. The image is 1080p hi-def video, normally with DTS-HD Master Audio lossless surround sound, although Dolby lossless may also be used. Blu-ray is the only popular format for 3D, which can be viewed on either shutter or passive-type 3D displays. Some Blu-ray sets have two separate Blu-ray discs, for 2D and 3D, while others have only one disc, on which the second image can be turned off for 2D viewing.

For a short time Blu-ray had a competitor in Toshiba’s HD DVD format, which was withdrawn in 2008. Rewritable Blu-ray drives for computers are now available, which can store up to 50 GB of data on a single disc. Blu-ray has been adopted faster than the DVD format was at a similar period of development. Although it faces competition from video on demand (VOD) and downloads, rental of Blu-ray discs is keeping the technology affordable while allowing it to move forward. Studios are releasing movies in combo packs with both Blu-rays an DVDs as well as digital copies for iPods and computers. Some movie bonus features are only available on the Blu-ray version, not on the DVD. Music Blu-ray releases have expanded greatly, though most music Blu-rays are not stocked by rental outlets or streaming services, thus requiring purchase. BD-Live allows players with Internet connection to access additional and updated videos and information on studios’ websites.


Hi-Res is – at least in our definition – any digital format that uses a sampling rate greater than the normal 44.1K/16-bit of standard compact discs. The now-obsolete format of DAT used 48K sampling, which made only a very subtle improvement in fidelity. The “word length” of 24 bits seems to enhance audio quality more than the increase in sampling rate. The current rates used in both original PCM (Pulse Code Modulation) digital recording and being made available as downloads by an increasing number of sites are 88.2K, 96K, 176.4K and 192K, all with 24-bit word length. The higher the sampling rate, the more space the audio files will take up on a hard drive, which is why MP3 files use serious data reduction to throw out less important musical information in order to squeeze the information onto small hard drives. They don’t approach the sampling rate of standard CDs although many claim “CD quality.” While most such PCM files are only two-channel, it is possible to realize multichannel PCM files.

We now include audiophile vinyl reviews in our Hi-Res Section because at AUDIOPHILE AUDITION we feel that that analog format, when properly done, can equal or surpass the fidelity of the top digital hi-res formats. This is especially true of 45 rpm 12″ audiophile discs, which can approach the aural achievements of direct discs of the past. We also sometimes include recent enhancements to the standard compatible CD format, due to their often improved fidelity – even though they are not actually hi-res due to their having to conform to the 44.1K/16-bit specs of standard CDs. These discs now include HQCD, xrcd24, K2 HD and Blu-spec CD. HQCD stands for High Quality CD, and is pressed onto improved-transparency polycarbonate plastic, plus the reflective layer uses a special alloy instead of aluminum. HDCD is an encode/decode process used on some CDs; though compatible for playback with no decoding, it can subtly enhance fidelity when properly decoded. The enhancements of these various compatible CDs can range from barely noticeable to near-astounding.

Since the fidelity of 128kpbs MP3 audio files is very poor due to the extreme data reduction used to enable more files to fit on small hard drives, discerning users of digital audio files use the highest MP3 sampling rate of 320 instead. But even that is much lower resolution than standard 44.1K/16-bit compact discs. The online downloads from the Apple iTunes store are 128kpbs AAC files and most of the other audio downloads on the Internet are 128 MP3s. Recently several hi-res commercial download sites have come into existence offering 96K/24-bit and even 192K/24-bit stereo audio files at a somewhat higher cost. Some even have a few multichannel offerings. Most are easily-decoded lossless FLAC files. Those with hi-res home music server systems can download the files directly to their hard drives and enjoy the highest fidelity possible today.

Hi-Res Downloads = The standard format for stereo music downloads, such as from the iTunes Store, has until recently been highly lossy MP3 files, which at the popular 128 kbit/s sample rate are about 1/11 the size of standard 44.1/16 CD audio files. There are now many different online services offering hi-res audio downloads, which have a fidelity and clarity far superior to standard CDs and certainly way beyond MP3s. There are even a few surround sound offerings.

The first genre served was classical music, but now many pop, rock and jazz releases are being offered as hi-res downloads. Of course these audio files require more memory space, but the popular free lossless FLAC codec, supported on most operating systems, works sort of like Zip compression and cuts file size about in half. Most digital studio sessions are now recorded in the 96K/24-bit format and that is the most popular hi-res format, often sold as a “studio master.” Other rates include 48/24, 88.2/24, 176.4/24 and 192/24. Pricing generally goes up with increased sampling rates. See our regular features on hi-res downloads.


CD+DVD = DualDisc was a double-sided 5” optical disc developed by the RIAA in 2004, but it failed due to the increased disc thickness jamming some players. Some DualDiscs had one side DVD-Audio—another mostly failed format—instead of standard CD.

Now a number of albums are being released as a combo of two discs—one a standard CD and the other a standard DVD. Often the program is the same, but the DVD is a video and can even have a higher resolution surround track. Others differ between the CD release and the accompanying DVD. Now there are beginning to be CD+audio-only Blu-ray combos, which offers the highest resolution lossless surround, while the accompanying CD can be played in portables, computers and cars.