On Thu, 04 May 2017 20:37:42 +0300, Iain Churches wrote:
"Brian Gaff" wrote in message
news
Did they decide to make audio and video optical formats play from the
inside outwards?
Was it simply due to the idea of making variable sized discs? IE if you
look at, for example early copies of James Last Tango, or Roxy Music
Avalon you see that there is a huge part of the surface not used and
it can be used as a mirror. Perhaps back in the day, it was thought
that one could crop off the disc so not only could we have singles
sized ones but old vinyl album length ones as well.
Nowadays of course the whole surface looks used even when its not.
Makes you wonder if there is some secret info in those outer areas....
Brian
When analogue disc recording was in development,
it was suggested that they too should play from the inside outwards.
For classical music this would have made a lot of sense as the final
movement of a symphony is usually the loudest:-)
The CAV analogue disk storage format was going to suffer from tracing
distortion problems one way or another. They just chose let it be 'the
other' end that was going to pay the price for the greater physical
storage space efficiency of a recording collection over that of the
cylinder format's constant linear analogue storage density and fixed
track pitch.
When a recording fits the chosen size of disk 'with ample room to
spare', you can console yourself with the fact the recording will suffer
less tracing distortion towards the end. In the case of recordings, as
pointed out above, which end in a loud crescendo, avoiding this innermost
wasted space affords a considerable reduction in the audible distortion
that would otherwise arise.
When it comes to optically read media, it makes more sense to read a
spiral track from the inside outwards. The innermost area is less prone
to contamination by handling and offers a fixed radial distance reference
point for the laser head servo controller to target when initialising a
freshly inserted disc.
With optical storage of digitised audio recordings, the CD provides a
constant bits per inch of track storage density resulting in a starting
RPM of 600 dropping to 270 RPM at the end of a full 74 minute recording.
IOW, there isn't the equivalent issue of 'tracing distortion' as in the
analogue disk system so the choice of which end to start following a
spiral track from (inner or outer) is otherwise quite arbitrary with
regard to the final audio quality.
Back in the eighties when a "Final Solution" to Hi-Fi storage and
distribution alternative to vinyl records and music cassettes was being
developed, the optical disk looked to be *the* 'Holy Grail'. It had the
charm of being a technically complex format that no consumer would be
able to afford the cost of duplicating without noticeable loss in audio
quality, yet be just as easy to create copies of by the millions for
distribution as vinyl records, indeed, it would be even cheaper so, as
the naive music recording industry thought at the time, a "Win-Win"
situation for them.
The only part of the music CD standard they got right was the stereo 16
bit interleaved LPCM encoding at 44.1KHz sampling rate used as the
bedrock of the CDDA standard. As for the optical media itself, that
acquired the status of "Legacy Media" well over a decade ago.
The CDDA encoding standard turns out to be amply 'over-engineered' to
completely serve its purpose as *the ultimate* replacement for the
classic stereo vinyl record (or even a 15 ips half track stereo recording
on modern quarter inch reel to reel tape using a high quality tape deck
with glass/ferrite heads, virtually free of head scrape noise).
Meanwhile, modern solid state storage techniques have long since made
optical storage obsolescent leaving the user the choice of which file
storage format to use with their "32GB micro-SD card the-size-of-the-nail-
on-my-little-finger" to store the equivalent of 40 full length Music CDs
with room to spare without resorting to any form of compression
whatsoever.
The only benefit, as I see it, in the music industry deciding to add SACD
as a 'premium offering' is that any attempts at enforcing DRM will be
concentrated on the 'premium product' leaving the 'ordinary base
standard' CDDA product free of any such DRM nonsense. :-)
--
Johnny B Good
Why?
Linear Mode
