Add, subtract, multiply, divide, logic operations ...

[Magnus Danielson]

> Bert Schiettecatte wrote:
> > > eg... You have two sines, one at say 400hz and another at 800hz. He
> > > doesn't wanna hear the two waves "mixed" together (thus you hearing
> > > two tones an octave apart), but what he wants is to hear the result of
> > > the voltage values of the waves being added together at various points
> > > in the time domain.
> > 
> > finally. somebody understands what I mean :)
> 
> I still don't understand.  If you add the instantaneous voltages of
> two signals, you're mixing them, right?  or what distinction am I
> missing?

In this case does mixing imply that you add them (or possibly subtract them).

> One possible issue: if you mix those two sines, you'll hear a single
> sound, pitched at 400 Hz, with some second-harmonic content.  You
> won't hear them as separate sounds, unless you carefully listen for
> separate partials.

Rigth, but how you preceive the result of the mixing is a diffrent thing then
how they are mathematically being "mixed". It is the superposition principle
that allows us to add two signals in order to have them occuring at the same
time and being interprented as two separate signals even if they occur at the
same time.

Now, from the 400 Hz and 800 Hz example we can directly learn that the ear has
a diffrent view on how these two tones are being perceived. However, if the
exampled would have been two more distinct frequencies such as 523.25 Hz and
659.25 Hz we would be able to hear two distinct tones from the well tempered
scale...

Picking two tones where one is the interger multiply (in frequency) to the
other will just confuse the debate... so if we talk about ear perception we do
that, if we talk about mixer's and simple math's function we do that... and 
then
we migth "mix" the debates together... if trying to do it in another way have
a tendency to creat noumerous misunderstandings and we are just bashing each
other...

> > now that this is sorted out ... does ANYONE HAVE THESE SCHEMATICS ? :)
> 
> You can add signals with a simple op-amp circuit.  I'd suggest
> Horowitz and Hill, but I don't know if that's available in Belgium.

I agree that the book "The Art of Electronics" by Horowitz and Hill is a good
book on the electrical subtleties... I recommend it.

Maybe a few schematics of a few mixers wouldn't hurt either... just to see how
things are being implemented here and there... I think we all tend to assume
that everyone knows what happends in a mixer and then goes to discuss the more
interesting details of dit and that filter...

Everything is difficult until you have mastered it. We all have been there not
knowing.

It is really time for a serious down to basics DIY website ranging from simple
things as resistor based voltage divider, various simple op-amp stages over to
description of various terms and example circuit of how such things can be
implemented. The web can be a great pedagogical tool if used rigth, it can also
be a heck of bastard really killing all interest and swamping all your time for
nothing tool (as so many pages do nowdays)... so just "any" site will not do.

Cheers,
Magnus