the outputs are different weightings of the bits on
the shift register. one is linear (n+1) and the other
is exponential (2^n). the exp is the common way to
interpret binary words, with a MSB and LSB etc. but
the linear gives a different responce. so that is why
the bits are connected to the dac's, because the
output is a interpretation of all the bits in the
register as an 8-bit word.
as for the brownian noise question, i think it dosent
apply since the relationship between one output level
and the next is not what the "change" control
dictates. instead it controls the probability that
new data will be loaded in the top bit.
hope that helps.
skot
--- Justin Modra <nitrohepcat@yahoo.com> wrote:
> Dr Maduce:
> Thanks very much for the reply.
> I'm still not sure why a plain old op amp and FET
> won't work instead of an OTA - other than the OTA
> provides a variable resistance. Well, I'll have to
> research this some more with my OTA and Norton Op
> Amp cookbook.
> - Justin
>
> PS - Here's a NOISE RING question for the group:
>
> "n+1" AUX OUT is a voltage based on a number between
> 0 and 255 plus one. Each value of n is related to
> the next as allowed by the CHANCE and CHANGE
> settings. Is this a simulation of Brownian motion?
> (Ref - Fractal Geometry of Nature by Mandelbrot,
> pages 12, 13, 233)
>
> But what does the "2^n" OUT voltage represent? 2^255
> is 58E75.
>
> And in the block diagram for the NOISE RING - why
> does each bit in the shift register have a line
> connecting it to the DACs?
>
>
> drmabuce <drmabuce@yahoo.com> wrote:
>
> Hi Justin
> i hope you will forgive the intrusion, as your
> email
> specifically addressed Grant. And i hope Grant will
> respond as well
> because you can bet he will have something
> interesting to say. But
> your question is just too juicy to pass up. It
> touches on a lot of
> very critical issues concerning analog module
> designs.
> An "OTA" (Operational Transconductance
> Amplifier) can be
> used as a PRECISION voltage controlled resistor (it
> has other
> applications as well but that's a whole `nother
> story).
> Analog synthesis is one of the realms where voltage
> control is STILL
> , pretty much, THE crucial method of control. A
> device that turns a
> voltage into a resistance is one of the handiest
> things designers can
> have in their toolkits when they set out to steer
> voltage on complex
> courses. Now, there are a bunch of components that
> can pull this
> conversion off. Diodes, Transistors,
> Photoresistors, even
> M.O.V's can do this trick too. But the
> distinguishing feature of
> the OTA is it's PRECISION. i don't know of any other
> analog
> component that yields 1v/octave scaling as
> painlessly as an OTA.
> That's why they're so desirable. Tom Henry of
> Midwest Analog
> Products wrote a terrific little book called `Making
> Music with
> the 3080 OTA.'
> http://www.midwest-analog.com/catbooks.html
> It's a great source of information on OTA's in
> general, not
> just the venerable and capricious 3080.
> Another issue is why they're becoming so rare.
> The quick
> and dirty answer is that `science' marches on, but
> money
> SPRINTS ahead. It's a digital world now. The entire
> commercial
> analog hardware `industry' is barely more than a
> hobby for
> about a couple dozen people. It's ENTIRE annual
> financial
> input/output is the equivalent of one smallish
> owner-operated
> american tavern. Digital hardware designs and
> software yield much
> greater precision and economy. The synthesizer -
> industry � moved
> there 20 years ago, so thoroughly in fact, that even
> experts are now
> hard-pressed to discern quickly whether an order for
> that synth you
> see in an EM ad will bring an actual synthesizer,
> or a little
> cardboard box with a disc in it to your house (hint:
> the price is the
> best criterion). Digital hardware (and so much less,
> softsynths) have
> no need for OTA's. The cheapest DAC can outperform
> the best OTA
> in a contest for precision. So just like steam
> engines the economy
> sets the context and OTA's are obsolete.
> So everybody knows that they don't make
> ARP2600's
> anymore but it's less widely known that they don't
> make the
> components with which you could MAKE (or repair)
> ARP2600's
> anymore either. Modern hardware design is
> standardized on
> surface-mount (SOIC) chips (even Grant used this
> method for the
> noiz-ring). These chips are TINY � about the size of
> a booger .
> They have the advantage of being cheap, and
> plentiful and, to be
> fair, many of the `greatest hits' of the analog chip
> world
> are still being manufactured in SOIC packages. But
> these lilliputian
> critters are designed for the convenience of
> automated assembly lines
> not human fingers. As Grant has pointed-out,
> manufacturers have
> stopped making many OTA types altogether So the
> only stocks in
> existence are in the discontinued stock of
> distributors and prices
> are adjusted accordingly until they're all sold and
> then it
> becomes an auction. In this sense EVERY piece of
> analog gear is a
> limited edition!
> This screed is not the whole story of course,
> there are many
> corollaries to the axiom "all things must pass' (the
> tube
> renaissance, handmade discrete op-amps etc.) but
> beware! I can
> prattle on for hours about that too!
> i can't say this enough: get `em while you
> can.
>
>
>
>
>
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