| Abbreviation | Meaning |
|---|---|
| SACD | A music disc format |
| ISO | A disc image stored in a file |
| DSD | A way of encoding digital audio |
| DST | Lossless compression of DSD data |
SACD — looks like a CD, works differently
Super Audio CD is a disc format developed by Sony and Philips. It can contain stereo recordings, multichannel recordings or both. Not every album has a surround mix: that depends on the particular release.
Hybrid discs also contain a separate standard CD layer, which a regular CD player can play. Reading the SACD layer requires equipment that supports SACD. A “DVD” or “Blu-ray” label on its own does not guarantee that support.
DSD — how the music is encoded
Audio on the SACD layer is encoded as DSD, or Direct Stream Digital.
A regular audio CD uses 16-bit PCM at 44.1 kHz. SACD uses a one-bit signal at 2.8224 MHz, known as DSD64. Comparing these numbers without considering the encoding method is misleading. “One bit” in DSD does not mean poor sound: it is a different way to encode the signal.
DSD music can also come as individual DSF or DFF files. You do not need a physical disc to play those recordings. You need software that supports their format.
ISO — a whole album in one file
In the SACD context, an ISO is a disc image. Rather than a separate file for every track, you have one larger file containing the album’s structure.
Here is the catch: the .iso extension does not tell you how the audio inside is encoded. A player must recognise the SACD structure and handle the data it contains. “Supports ISO” is therefore too vague: a music disc image and an operating system installation image can share an extension while containing completely different things.
DST — compression that keeps the audio data
DSD data takes up considerable space. DST, or Direct Stream Transfer, compresses it losslessly: decompression restores the original DSD data.
Think of putting a document in a ZIP archive. A smaller file does not mean missing sentences.
This creates another possible snag: a player may support DSD without supporting DST. One SACD ISO image plays and another does not, despite the same extension. FiiO documented precisely this kind of compatibility issue.
Do you need a special player?
Playing DSD files does not always require special hardware. Software can convert DSD to PCM and play the music through a conventional audio output.
Sending DSD to a digital-to-analogue converter without that conversion requires compatible software, a suitable connection and a compatible converter. Reading a DSD file and sending DSD to a device are two different capabilities.
Before shopping for new equipment, check three things: what is inside the file, whether the software can read it and how it sends the audio. A few letters in an album description are not, by themselves, a reason to buy new hardware.