[sdiy] RE: [AH] control voltage was/ Keyboard in space

[Grant Richter]

> Since we are on the subject.  I understand the flaws in a midi setup. 1 to
> 127 is not a fine enough resolution for most modulation activities.  I
> understand how wonderful the voltage concept is in its infinite resolution
> (superstrings?).
> 

What we are trying to do is transmit "information". Information is an
abstract concept which is not very well understood. Both "analog" and
"digital" are information analogues using different encoding schemes.

When we use electricity to represent information, we must use some kind of
encoding and decoding procedure. The most direct method is to use the
"voltage" (a simple to measure quantity) to represent the number. So the
number +10 is represented by a +10 volt signal. This signal is always a mix
of intended and unintended signals (noise), but has extremely fine
resolution.

You can also represent the number in binary (base 2) form as 0110, but this
has drawbacks because we are "rounding" the number to fit a limited number
of slots. This is called "quantization" and produces quantization noise,
also called zipper noise. Binary encoded systems also need to be "sampled"
which is time limited, and produces "aliasing" noise. These additional noise
sources can be minimized with proper design.

Both methods have advantages and disadvantages, binary encoding CURRENTLY
does not carry as much information as the original voltage signal. So the
information content has to be reduced to fit the current binary encoding
scheme. A widely accepted theory is that much information is redundant and
can be thrown away. This works OK for telephones, but some people feel music
suffers from information reduction.

Simple, inexpensive devices to convert between the direct voltage encoded
system and the base 2 binary encoded system are available from:

MIDI to Control Voltage
http://www.paia.com/midi2cv.htm

Control Voltage to MIDI
http://www.paia.com/midibrn.htm

There are many other excellent dealers of this type of equipment. But to my
knowledge, only PAIA makes devices to go in both directions.