[A6] Some waveform observations

[Chad Gould]

On 21 Nov 2004 at 11:18, Robert Skerjanc wrote:
> 1. the basic waveforms of the VCOs look very strange, when you see them 
> on an oscilloscope. "Saw" is not a saw wave at all, also the other 
> shapes are not mathematically geometrical, but they sound as they 
> should. Is this a specialité of the A6?

This is actually *typical* of a pure analog synthesizer and probably part of the reason 
why analog-generated synthesizers even today sound more "alive" than any given 
modelled synthesizer. Pure mathematical waves really are uber-mechanical 
sounding. Nice in some instances, but that's not what you buy an Andromeda for.

> 2. The VCOs have linear and expon. type of FM. Normally the linear type 
> is intended for the modulation to stay in tune (negtive slopes detune 
> the carrier in same amount as positive slopes), like the DX7. However 
> linear FM on A6 stays not in tune. Possibly the reason are the weird 
> waveforms mentioned above?

This actually is an unfortunate aspect of the Andromeda... the VCAs that control the 
linear and exponential FM are *not* tuned and calibrated per voice in the standard 
tuning routine. (I believe they are only calibrated during the VCA tune, but still it is not 
coded per voice. I can't quite remember the details. Somewhere in the long lost 
archives is a Mike Peake post with an even more technical explanation, describing 
why these VCAs couldn't be calibrated like the rest [cost reasons I believe was the 
final answer]...) 

Since this is an analog synthesizer, therefore, you will see some tuning drift between 
voice to voice. I think even session to session I've heard variance in an FM patch 
attempt I tried. 

It's a bit unfortunate, as this limits the ability to do both polyphonic analog FM (nuts!). 
However, by limiting the patch to monophonic mode, you can do pretty good with 
your FM. Though unless I'm mistaken about the slight variance from session to 
session I would limit FM patches to studio work only.