[PD] Spectrum graphing amplitude problem

[Martin Peach]

Mathieu Bouchard wrote:
> On Mon, 22 Oct 2007, Martin Peach wrote:
>
>> No. The spokes just look blurred. Have you? If you try it at night under
>> a streetlamp then you get the effect. I'm sure I have analog eyes ;)
>
> You have seen a lot of analog equipment and you know that it does 
> time-wise sampling. analog vs digital is not what we are debating.

Analog equipment works continuously in time. Digital is almost always 
clocked. If your eyes are clocked I'd like to see through them. If we 
are debating something here it involves a difference between continuous 
and discrete time systems, which constitutes part of the distinction 
between analog and digital in common parlance.
Photons impinging on my eyes drive the illusion of vision. My eyes do 
not choose to sample incoming photons. The photons cause the nerve 
impulses. As long as the light source is continuous, something I am 
looking at will not spontaneously disappear because the rod or cone 
isn't sampling it at any given moment, rather the rod or cone is 
continually integrating the photon flux and outputting a stream of 
pulses in proportion to the incident intensity; the output is an analog 
of the input. In the brain the streams of pulses could be interpreted as 
digital but the streams from all the receptors are not synchronized by a 
central clock so the overall effect is of a continuous-time system.

>
> anyway, analog electronics are what one uses to construct digital 
> electronics, thus analog electronics are very capable of 
> discontinuity. If you are not satisfied with thinking of human vision 
> as electric, you can extend the same reasoning to chemical processes 
> that complement the electric processes in use by neurons.

I never said any of that. I was responding to your implication that the 
aliasing effect seen in the spokes of a spinning bicycle wheel is caused 
by some sort of discrete-time sampling process in the eye, which is not 
the case. The aliasing is induced by illumination by a periodic light 
source which the mind interprets using a "most likely" scenario in which 
a spoke that reappears closest to one that was previously visible is 
probably the same spoke.

Martin