Sony MINIDISC - Manual (Page 9)

Shock-Resistant Memory
Conventional optical pick-up systems can easily
mistrack when subjected to shock or vibration. In
digital audio CDs, this causes “skipping” or
muting. Resistance to shock and vibration is a vir-
tual prerequisite for true portable personal audio
applications. In the MD system, Sony has solved
this problem with a unique shock-resistant
memory.
While the MD pick-up can read information off
the disc at a rate of 1.4Mbit per second, the
ATRAC decoder requires a data rate of only
0.3Mbit per second for real time playback. This
difference in processing speed enables the use of
a readahead buffer, placed between the pick-up
and the decoder. If a 4Mbit memory chip is used
for the buffer, it can store up to 10 seconds of
digital information. Should the pick-up be jarred
out of position, the correct information continues
to be supplied to the ATRAC decoder from the buffer memory. As long as the pick-up returns to
the correct position within 10 seconds, the
listener never experiences mistracking or muting.
Since signals enter the buffer memory faster than
they leave it, the buffer will eventually become
full. At that point, the MD player momentarily
stops reading information from the disc; it resu-
mes reading as soon as there is again room in the
memory chip.
Using a concept called sector repositioning, the
MD pick-up has the ability to quickly resume rea-
ding from the correct point after being displaced.
When signals are recorded on the MiniDisc (either
recordable MO or premastered optical media),
address information is assigned every 13.3 milli-
seconds. When a pick-up is shifted out of place,
the MD player quickly recognizes the disruption,
identifies the wrong address, and instantly returns
the pick-up to the correct position.
What it is and How it Works
A A D D C C D D
A U S T R I A
7
Decoder
4 Mbit Memory
Optical Pick-up
1.4 Mbit / sec
0.3 Mbit / sec
D/A converter Amplifier
Digital Music Data
Analog Music Data
Flow of Music Data
Shock-Resistant Memory