[sdiy] Is everything digital?

[Bob Weigel]

bbd's and switched cap filters are...sort of hybrids almost..but not 
really the way we think of hybrids in synths.  Add to that the EG's I 
just made not of for the Jupiter 4.  Using a variable clock to set 
charge rates on capacitors.  It's a digital control element interacting 
with an analog circuit.  As are the previous two example.  In pure 
digital circuitry, all that gets considered are 1's and 0's.  In pure 
analog- non-digital circuitry only continuous voltages are used.  As 
soon as you introduce a ...switch for instance, you have introduced a 
digital element of sorts.  It has two states.  On/off.   All synths I 
know of have at least a couple 'digital control' elements...; 
keyswitches and/ or trigger/gate inputs. 
    But anyway if it's our intent to properly convey the NATURE of the 
circuit design when we use these terms, we should try to express the 
elements of the circuit which are digital.  These things are just 
assumed in the cases of synths.  HOWEVER (and here's a thought for some 
industrious person) someone MIGHT create a device and....call it 'the 
world's first keyboard based totally analog synth'  hehehe.  And 
well...you know what i'm thinking right?  Put some kind of cool ...maybe 
even controlled enviroment...where you leave it plugged in all the time 
and a peltier device keeps it constant temp...key movement induced 
analog oscillator/resonator circuit instead of key switches in the 
keyboard.  I've thought of doing something like this someday when I have 
the funds.  Create a new totally analog touch interface of some kind 
where each note has a unique character like a rhodes.  Then perform 
analog synthesis on all those.  Would that be sick or what?! :-)  
Probably would be back to weight 150lbs too.
       Anyway all that to say that there are digital aspects to bbd's 
and switched cap filters but there are also non-digital aspects.   While 
the final factor to consider in 'should we apply the word digital to 
this circuit?' is the signal information itself, sometimes the digital 
aspects in schemes like switched cap filters can be more detrimental to 
what we like hearing in analog than just going all digital. :-)  I guess 
they've improved them some.  I haven't listened to one for some time.    
-Bob

Magnus Danielson wrote:

>From: The Old Crow <oldcrow at oldcrows.net>
>Subject: Re: [sdiy] Is everything digital?
>Date: Sat, 14 May 2005 22:24:15 -0400 (EDT)
>Message-ID: <Pine.LNX.4.44.0505142209580.3063-100000 at crowsnest.oldcrows.net>
>
>  
>
>>  My only other comment on this topic is how I perceive digital vs. 
>>analog:
>>
>>  discrete time domain = digital
>>
>>  continuous time domain = analog
>>    
>>
>
>Nope, that's not it!
>
>You can have discrete time domain in pure analogue too. There's bunches of
>switch capacitor filters out there in real life to prove me right.
>
>There is actually two independent (ortogonal) things happening:
>
>* Continous vs. Discrete time scale
>* Continous vs. Quantified signal level scale
>
>In traditional "analogue" you have continous time and signal level.
>In traditional "digital" you have discrete time and signal level.
>
>Put a signal through a comparator, a schmitt trigger or quantizer and you have
>continous time scale but quantized signal level. Not quite "digital".
>
>Put a signal through a sample and hold stage, and you have continous signal
>level scale, but discrete time scale. Not quite "digital".
>
>Infact, you can have _both_ discrete time and signal level scale, without
>really be "digital". In "digital" we transport signals in binary (or on odd
>occasions other modulations forms like trinary), but many times we define the
>signal as being one or more of the transporting bits, and for continous signals
>(sampled) we often use Pulse Code Modulation (PCM).
>
>I strongly recommend the reading of Shannons article on digital telephony from
>1948. Briliant motivation for the concept. In the Appendix the now called
>"Nyquist theormem" is being prooved, but with a error in the proof I might add.
>
>Cheers,
>Magnus
>
>
>  
>