> From: Stainless Steel Rat [mailto:[EMAIL PROTECTED]]
> * Steve Hill <[EMAIL PROTECTED]> on Wed, 06 Jun 2001
> | I see no reason why you cannot compare the bandwidth and/or space
> | requirements of digital and analogue recordings. Given that
> all recordings
> | are ultimately stored as an analogue form,
>
> You are assuming that digital signals are modulated into
> analog signals for
> recording, like on your old C64 (which ammounts to recording
> the noises a
> telephone modem makes and playing them back later). There is no such
> modulation involved with digital audio storage.
No, I merely refer to the fact that the real world is analogue and that the
digital data, though not used to modulate a carrier, are stored as an
analogue waveform, which approximates those data. On a CD the laser is
reflected off the disc, onto a photodiode which produces four analogue
voltages. These are then used to perform tracking and linear speed
adjustments, and are also processed to produce the digital data. The signals
could just as easily be used to produce an analogue audio signal.
[snip]
> | Of course, the advantage of digital audio is that it is more easily
> | possible to remove the noise introduced by the medium -
> albeit at the
> | expense of adding redundancy and the introduction of
> quantisation noise -
> [snip]
>
> The advantage of digital audio is that as far as consumers
> are concerned it
> does not wear out.
No. The advantage of CD and MD against vinyl and tape is that they do not
wear out. The fact that the former are digital and the latter analogue is
co-incidental. DCC and DAT both wear out yet are digital. Laser discs were
entirely analogue and do not. Admittedly, due to the error correction,
digital recordings will handle wear better for a while before failing
completely where as analogue recordings deteriorate more gradually, but it
is the medium that determines whether wear occurs.
> | - but I am given to understand that, to achieve recording
> of the same
> | perceived quality, PCM - whether linear or non-linear
> | - will require a greater bandwidth than to record directly
> in analogue.
>
> And yet, the fact remains that when analog recordings are
> made on "digital"
> media like Compact Discs, the effective capacity of the media is
> significantly reduced compared to its equivalent digital counterparts.
I'm not sure that I understand the point that you are trying to make here.
I've not heard of anyone storing an analogue signal on a CD but, given that
a CD provides 74mins of bandwidth at several MHz and you only need 44.1kHz
(2 * 22.05kHz channels) to store the analogue signal held on it, you could
store around 100 digital CDs on one analogue CD. However, it would be a pig
to produce and the play back equipment would be more complex. It would still
not wear out, though.
Steve.
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