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

[Magnus Danielson]

Here I go again...

> Ya' know... I can't tell you how many times I looked at those numbers and
> tried to (extrapolate and) visualize the resulting waveform. When I saw the
> weird spikes happening... It didn't make sense, but I kept doing the math
> and it kept coming out the same.
> 
> Is this where I blame it on the 3rd grade math homework I was doing last
> night? I guess I better call my son's teacher and explain... :)

Is it you or your son that does the homewaork? Who does it best?

> Cool... I'll blame it on the kid.
> 
> (man... I can't believe I did that... what a brainfart... It must be that
> tumor)

Well, we all work to contribute to your tumor... eh... anyway... eh... :)

> >  As far as I'm concerned, a summing circuit, adds together the voltages at 
> >  any point in time.
> >
> >  Period.
> 
> But... And I'm refering to something further down in your message and
> something you said earlier... In a mixer, if I split a 1v signal into
> channel one and two, then given unity gain through the mixer, what I hear
> on the output isn't a 2v signal.
> 
> Is it?

It can be. If your splitting does not cause the 1 V signal to reduce, and that
the two different paths does not have a different phase and amlitude function
and that both paths have a 1:1 signal level gain and that the signals are
added and not averged at the mixpoint, then you can get 2 V. There numbers of
ways to get 2 V when any, some or all of the above conditions are not met, but
then your question is irrelevant, rigth?

> >  When you mix (a.k.a. "add") the voice of, say, William Burroughs with the
> >  sound of, say, a hip hop beat, the fact that you
> >  can still recognize each sound in the mix doesn't mean that the sounds 
> >  haven't been modified by adding them together - they've been modified
> >  quite a bit. In fact I would challenge you to ever get back either of the
> >  original sounds. The sounds have been added together - period.
> 
> I agree. There will be a mashing of the audio at any point in time where
> common frequencies occur in the two audio inputs.
> 
> The other side of this is that if I mixed a 400hz sine with an 800hz sine,
> I *could* get the original signals back.

For the sine example it is simple to separate them, for a complex signal it is
no longer as easy... it is certainly not easy... one has to use the rigth 
tricks
to start with (and yes, I have some ideas... put I'll keep them to myself for
a while :)

> Christopher, I guess what I'm tripping over is using "added" and "mixed" as
> synonyms. I see adding as a mathematical process (ummm, a proper one), and
> mixing as a way to hear two sounds simulaneously, but they aren't
> necessarily *directly* interacting with one another. I understand that
> acoustically they will interact all over the place, this is the pleasure
> (or dread) of sound. But if you shoot one sound out of the left channel and
> another out of the right, then the only space that the signals will cross
> is in the air. Will the mixed/added sound that your brain percieves be the
> same as mathematically adding the two signals and then playing the result
> in mono from both channels? Obviously, you'd have to find a way to squelch
> your brain of the left/right spacial issues. ie, you wanna be able to hear
> in mono.

The ear is a complex thing and what you can and not can distingish with it is
not allways easy to predict. There's a CD called "Auditory Demonstrations"
made by Philips which is quite enligthening to listen to. It comes with a thick
booklet and it is worth reading and listening carefully.

Note also that it is quite uncommon that a certain sine occur alone, so that we
can distinguish it from another one as the amplitude of the instrument it 
builds
up changes....

For me is the word mixer just a common word for a device that will take 
diffrent
things and "mix" them together in some kind of way. If that is audio signal,
RF signal or onions and garlic neither of these really points to a specific
method, even if I can describe the method for each usage of the word.

Cheers,
Magnus