LINGUIST List 4.769

Tue 28 Sep 1993

Disc: Technology: CD versus MiniDisc

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1. Stephen P Spackman, Re: 4.739 Summary: The MiniDisc

Message 1: Re: 4.739 Summary: The MiniDisc

A few technical comments based largely on comparison with CDs, which
I've had too much to do with over the years....

|The MiniDisc uses a laser beam to record and read digitally coded
|data. It works by compressing the digital data with a 4-1 ratio
|compressing algorithm, and it's able to fit 600 megabytes (!) of
|memory on a 128 MB disc.

Compare this with a CD, which has around 600M of *real* storage, and
remember that any compression technique with a fixed compression ratio
is "lossy" - with a 4:1 ratio, at least 3/4 of all signals can't be
encoded accurately (hopefully not including any you care about!).
Compression isn't magic: that's 600 meg of raw _data_, represented
(approximately) in 128M of _memory_ (meaning: that which is NOT
forgotten). This is not "really" a lot.

|Access time, editing and programming: Reportedly, the access time
|is as fast as (or faster than) one in a CD.

We could have hoped for an order of magnitude faster; CDs are
notoriously slow. If access times are only comparable to a CD, this
medium will not be useful for direct segment-splicing or other
full-bandwidth computer-driven applications.

Problems mentioned with space reclamation are probably related to
excessive seek time causing loss of sound continuity with a
discontiguous recording pattern.

|o "multiple generation copies": A couple of people said that
| after the 10th generation of digital copies (MD-MD) frequencies
| start to be lost. This refers to digital copies, not to the
| original MD, of course. So, it seems good enough.

This *ought* to be impossible. If these are digital copies, not analogue
ones, then the player is tampering with the signal *on purpose* and we
should raise hell with the manufacturers.

| One obvious drawback that I see is
|the impossibility (in current MD models) to slow down the
|recording for easier transcription -- particularly when dealing
|with conversational data.

The "obvious" mode of use of digital media is to play back through DSP
equipment hosted by a computer, with such services provided by the DSP
rather than the player itself; then the player need only be willing to
provide "bursty" (slow-on-average) transfer. The question is, will SONY
care to provide adequate computer interfaces at a reasonable price, or
(as with CD and DAT) will they take this as an excuse to stratify their
pricing structure? Somehow I suspect they'll prefer money to goodwill
:-).

| One person from the MD-L
|list (I think) suggests that minidiscs could reserve more space
|for text data, so that entire songs (or conversations) could be
|entered and displayed either on the LCD or on an external monitor.

If the ratio is indeed fixed, that is a near-criminal act of misdesign,
especially since the availability of textual annotations was (I thought)
to be a main selling point of the medium.

It is sad that the technology to do these things "right" has existed for
years, but marketting strategy prevents them becoming available for
reasonable prices. But at least things do slowly improve....
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