[sdiy] Silly vector synth question

[Richard Wentk]

I'd guess it works like this:

Component 1 is a simple four axis volume control, with zero in the middle. Pushing the stick N scales the N output from 0 to 1, but with no S. Pushing it S scales from 0 to 1, but with no N. E+W work similarly.

Component 1 gives you the correct mix around the edges, but creates a zone of silence towards the middle. 

Component 2 is a static 0.25*(N+S+E+W) mix of all four components that fills in the zone of silence. 

The relative mix of 1+2 is scaled by the *radius* from the centre position. So when the radius is 0, you get component 2 only, with the correct centre mix. When radius is 1, you get the edge mix from component 1. 

For all other radius values, you get a correct proportional mix of all four components.

Doing the rect to pol conversion is slightly more work, but you only need to do it for each control change. 

I'm not sure linear scaling covers this. At - say - NE, you should get 50:50:0:0. If you use linear scaling, you get some element of W+S mixed in, because the x & y distances from W+S aren't 100%.

R

On 6 Feb 2011, at 12:40, Tom Wiltshire wrote:

> Thanks Gabriel. I'd had the same thought and have just been reading the Prophet VS user manual.
> 
> What I found most interesting is that if you push the stick North, you get 100% of that oscillator, not the 2/1.414/1.414/0 mix that Gordon suggested.
> Furthermore, pushing the stick hard NW gives 50% / 50% / 0% / 0%.
> I'm going to have to think about what they did to the simple X and Y position to get those numbers. It means the two axes are not independent, since the amount of E and W is affected by the position on the N-S axis.
> 
> T.
> 
> 
> On 6 Feb 2011, at 12:22, Gabriel Lindeborg wrote:
> 
>> Hi All!
>> 
>> In birth of the Prophet VS Chris Meyer writes:
>> "The first major change to the Diamond Patch (a name that curses Vector Synthesis to this day...it would be much easier to use if the four oscillator positions were the corners of a square instead, but Josh [Jeffe] felt the name demanded that the user interface arranged them like a diamond -which everyone has followed ever since) was to allow the four waves to be separately tunable."
>> 
>> The "Sequential Circuits Prophet VS Owners Manual" (page 6-5) goes on to say:
>> "To exploit the sonic power of four oscillators, Sequential engineers turned to the basic concepts of analytic geometry and found a very elegant solution in the Cartesian coordinate system. By assigning an oscillator to each of the four poles, a single point can simultaneously represent the mixture level for all four oscillators. For example, if the mixture point is exactly in the oenter (at the "origin"), you have an equal mixture of all four oscillators. Of course as the mixture point moves away from center, the oscillator(s) towards which it heads become louder and the oscillator(s) it moves away from get softer.
>> The basic way to move the oscillator mixer point is with the Waveform Mix joystick. Please see Figure 6-3 (next page). One dimension of the mixer (the "A-C axis"), is the blend of oscillators A and C, and the other dimension ("B-D axis") is the blend of oscillators B and D. 1'he mixer values for each oscillator are represented as percentages and always add up to l00%. So, when the joystick is centered, each oscillator level is 25% of the overall mix. One oscillator can have 100% of the mix."
>> And on the following page (6-6) four examples of stick position and mix result can be found.
>> 
>> Both documents are available at the web.
>> 
>> //Gabbe
>> 
>> 
>> Tom Wiltshire skrev 2011-02-06 12:15:
>>> On 6 Feb 2011, at 10:26, Gordon JC Pearce wrote:
>>> 
>>>> On Sat, 2011-02-05 at 22:48 -0800, DTK wrote:
>>>> 
>>>>> Its not so much about the proximity to center as it is the distance between
>>>>> the outlying point and the current stick position, if that makes sense.  If
>>>>> you think of it in terms of linear distance, when you move the stick to the
>>>>> far north position, you are (obviously) farther away from the south, but the
>>>>> distance to east and west also increases significantly as compared to the
>>>>> center position.
>>>> Ah! so if I have the values so that with the stick centred I get:
>>>> 
>>>> N = 1, S = 1, W = 1, E = 1
>>>> 
>>>> then when I move the stick north I should have:
>>>> 
>>>> N = 0, S = 2, W = 1.4142, E = 1.4142
>>>> 
>>>> because I'm calculating the hypotenuse of a triangle between the centre,
>>>> the stick position and the oscillator.  That makes more sense.
>>>> 
>>>> Gordon MM0YEQ
>>> Does anyone know if the Prophet VS worked like this too? (Aaron? Don't you have a VS in your rack somewhere?)
>>> 
>>> It seems like more sums than are really necessary, but I suppose it has the advantage of getting you closer to having just a single oscillator when the stick is pushed to an extreme. I should really have a play with this.
>>> 
>>> T.
>>> 
>>> 
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