Editing MiniDisc (section)

=== Audio data compression ===
The digitally encoded audio signal on a MiniDisc has traditionally been [[Audio compression (data)|data-compressed]] using the [[ATRAC]] (Adaptive Transform Acoustic Coding) format.

ATRAC was devised to allow MiniDisc to have the same runtime as a CD. ATRAC reduces the 1.4&nbsp;Mbit/s of a CD to a 292&nbsp;kbit/s data stream,<ref name="wb-minidisc-bitrate">{{cite web|last=Woudenberg|first=Eric|title=MiniDisc FAQ: Audio Topics - What is the bit rate of the Minidisc's ATRAC audio after compression? |website=Minidisc Community Portal |url=https://www.minidisc.org/faq_sec_4.html#_q21|access-date=2022-07-30}}</ref> roughly a 5:1 reduction. ATRAC was also used on nearly all flash memory [[Walkman]] devices until the 8 series.

The ATRAC codec differs from uncompressed PCM in that it is a [[psychoacoustic]] [[lossy]] audio data reduction scheme. Like other lossy audio compression formats, it is intended to be acoustically transparent.

There have been four versions of ATRAC, each claimed by Sony to more accurately reflect the original audio. Early players are guaranteed to play later version ATRAC audio. Version&nbsp;1 could only be copied on consumer equipment three or four times before artifacts became objectionable, as the ATRAC on the recorder attempted to compress the already compressed data. By version&nbsp;4, the potential number of generations of copy had increased to around 15 to 20 depending on audio content.

The latest versions of Sony's ATRAC are ATRAC3 and ATRAC3plus. Original ATRAC3 at 132&nbsp;kbit/s (also known as ATRAC-LP2 mode) was the format that was used by Sony's defunct Connect audio download store. ATRAC3plus was not used in order to retain backwards compatibility with earlier NetMD players.

In the MiniDisc's final iteration, Hi-MD, uncompressed [[CD-quality]] linear PCM audio recording and playback is offered, placing Hi-MD on par with CD-quality audio. Hi-MD also supports both ATRAC3 and ATRAC3plus at various bitrates.