MiniDisc Generational Loss Tests

One weakness MiniDisc has when compared with DAT is that perfect copies cannot be made (without professional equipment) due to the asymmetric nature of the MiniDisc audio compression system. Every time the signal goes through the compression/decompression process, it changes slightly. After several generations these effects become noticable.

One could argue that whether or not there is loss from generation to generation is a moot point since SCMS (Serial Copy Management System -- present on all consumer digital audio equipment) allows only a single generation of digital copying.

However professional machines exist which do not obey SCMS, and so the question remains, how bad are the effects of this generational loss? In order to discover this, I conducted an experiment which produced samples of audio copied up to 100 times.

I generated these samples as follows:

  1. Digitally copied from CD (Panasonic MASH SL-S490 portable player) to MiniDisc (Sony MDS-503 MD Deck), a short audio sample (Donald Fagen: Kamakiriad, Trans-island Skyway (track 1), 1:34-1:54)

  2. Digitally copied this segment back and forth from the MDS-503 to a Sparcstation 2 via a Townshend Computer Tools "DATlink" (workstation SCSI digital audio interface) 100 times (over the optical connector), saving each intermediate copy.
SCMS was not operative during these copy operations since the professional equipment used was not set to generate a copy restricting SCMS code.

A selection of the resulting generational copies are given below. (You may need to equip your Unix, Macintosh, or Windows system with an MPEG audio player to hear these.)

All samples are 20 seconds of stereo audio, 952KBytes each, MPEG Layer II at 384Kbit/sec.

I have chosen not to do subjective evaluations of these samples for the following reasons:

Based upon the reasons given above, I have chosen to simply provide these samples so that others may judge for themselves the effects of MiniDisc generational loss.

Eric Woudenberg, April 1996


The reasons for generational loss are examined in Frank Kurth's paper An Audio Codec for Multiple Generations Compression without Loss of Perceptual Quality (pdf).

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