[sdiy] what exacly is "audio" in electronics terms?

[Scott Bernardi]

OK, Ian took me to task on a misleading statement I made about it being
voltages in the patch cords. He's right, voltage doesn't flow, electrons do,
and it is the flow of electrons that make up a current.
In general we deal with voltages in synth module inputs and outputs (ie,
"voltage controlled"). Basically, you could run a current source output into a
direct short with no problem, but I wouldn't advise doing that to your VCO
output because it's a voltage source (low output impedence) rather than a
current source (high output impedence).  It would try to supply a huge current.
(Note: it's common practice to put a 1K resistor in series with outputs of
modules. As you plug your patch cords, you short the tip to the jack ground for
a short period of time, and the 1K resistor limits the current).
Module inputs have a high input resistance (typically 100k), and when you apply
a voltage to an resistance (impedence is like ac resistance and can be
frequency dependent), it draws a current according to Ohm's law  I = V / R.
You have this conversion from voltage to current and visa versa all over the
place in analog circuits.  For example, in a simple opamp inverter,  you apply
a voltage to the input resistor, and it is converted to a current Iin =
Vin/Rin.  This same current flows through the feedback resistor Rf (negligible
current flows into the opamp inverting input) which converts it back to a
voltage Vrf = In * Rf = Vin/Rin * Rf. Since the inverting input is a virtual
ground, the output is negative, Vout = -Vin * Rf/Rin.


Ian Fritz wrote:

> You're saying that voltage "flows"? Electrons are what "flow"!
> And signals usually include both voltage and current variation.
>
> ----- Original Message -----
> From: "Scott Bernardi" <sbernardi at home.net>
> Cc: "SDIY" <synth-diy at dropmix.xs4all.nl>
> Sent: Monday, November 26, 2001 6:33 AM
> Subject: Re: [sdiy] what exacly is "audio" in electronics terms?
>
> > It's voltage. "Audio" also designates that it is an ac signal in the
> > frequency range that is audible to human hearing, around 20-20khz (for
> > young pups, less high freq for some of us older guys). This is opposed to
> > control signals like gates, triggers, envelopes, keyboard v/octave
> > voltages, etc. which are sub-audio.
> >
> > Glue Sniff wrote:
> >
> > > what exactly is flowing through those wires and patch
> > > cords as, "audio" ? I have built many synths and
> > > effects pedals through the years,  but I am still in
> > > the dark about this most basic of questions. is it,
> > > amperage, voltage, resistance?  in the case of a sine
> > > wave what is it that is rising and falling?
> > >
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> > --
> > Scott Bernardi
> > sbernardi at home.net
> >
> >

--
Scott Bernardi
sbernardi at home.net