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Variable response offsets?
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Variable response offsets?
dooj88
Is there such a thing as an exponential offset? i'm not sure how useful it would be outside a macro-knob type patch... like using one channel of blinds multed a bunch of times as a master-control knob ala cold mac style..

while typing this, i thought of perhaps using the offset to trigger an AHR exponential envelope.. i can't really see why this wouldn't work... hmm
modularblack
The 3x mia has an exponential offset.
KSS
Any expo VCA can apply an exponential offset. An expo EG can be used to control a linear VCA for exponential offset. An audio mixer makes an expo offset available related to its audio taper pot. Many ways to patch in an expo offset.
dooj88
KSS wrote:
Any expo VCA can apply an exponential offset. An expo EG can be used to control a linear VCA for exponential offset. An audio mixer makes an expo offset available related to its audio taper pot. Many ways to patch in an expo offset.


i never mess with the response curves of the vcas since i never noticed anything other than distortion when changing them. i'll give this a shot, thanks.
Dave Peck
But an "offset" is simply adding a continuous DC voltage to any signal. It is neither exponential nor linear. It's just an unchanging voltage, with no 'response curve'.
KSS
Dave Peck wrote:
But an "offset" is simply adding a continuous DC voltage to any signal. It is neither exponential nor linear. It's just an unchanging voltage, with no 'response curve'.

While your statement taken alone is true, it's clear from the title of this thread that an exponentially applied offset was the request.

edit: Actually only your first sentence is true. There is no requirement that an offset be unchanging over time. /edit
pugix
KSS wrote:
Dave Peck wrote:
But an "offset" is simply adding a continuous DC voltage to any signal. It is neither exponential nor linear. It's just an unchanging voltage, with no 'response curve'.

While your statement taken alone is true, it's clear from the title of this thread that an exponentially applied offset was the request.

edit: Actually only your first sentence is true. There is no requirement that an offset be unchanging over time. /edit


I have to agree with Dave Peck. An offset by definition is a fixed DC bias. An 'offset' that changes dynamically contradicts the common understanding of the word. When we talk about response curves or shape, we're usually taking about how the output of an envelope generator changes over time. Strictly speaking, an envelope generator does not generate an envelope. An EG generates a voltage that changes over time in the shape that a VCA using it would impart to the signal. The signal is 'enveloped.'
mskala
You could have an offset controlled by an exponential knob (like the offset on my Transistor Mixer), or something that processes a CV input through an exponential function before adding it to another input (easy to patch with a fixed offset, an exponential DC-coupled VCA, and an adder). I'm not sure whether either of these is what the original poster wanted, but they're both reasonable things to do.
KSS
pugix wrote:
I have to agree with Dave Peck. An offset by definition is a fixed DC bias.

Allan Strange agrees. Ch 5 of his seminal book uses the term Offsets:Fixed Control Voltages. So there's that. I had the same thought and therefore had to edit the reply to include who says it has to be fixed?
Because the OP opened a thought that seems to have merit.

Offset by itself as a noun means fixed. No problem there. However, it seems rather an old school and limited way to view it and that is what is exciting about the OP question. What does the verb offset mean? What about the term variable offset, or in this case exponential offset? Those have a great deal more meaning than the alternative suggested by strict or pedantic adherence to Strange. What is the term for a voltage which initially sets the base level of some other signal? An offset. What happens when that voltage changes over time? That's called CV. If we're patched to allow a varying offset, can we call it offset CV?

Quote:
An 'offset' that changes dynamically contradicts the common understanding of the word.

Common understanding? Or just traditional meaning when not modified with additional words as seen in OP question? Please find no fight here. See rather an opening for possibly useful discussion.

Quote:
When we talk about response curves or shape, we're usually taking about how the output of an envelope generator changes over time.

That is a surprising statement to see from you. We talk about many other response curves and shapes which have nothing to do with EGs.

There is no dispute that the word offset used alone usually or traditionally means a fixed offset.
Can you see the OP's question as a way to look at something familiar in a different light and gain appreciation for better understanding a patch as a result. 'Apply a variable offset' ultimately has the same effect as 'apply a variable control voltage to a place or as a means to adjust the base level of a signal'. Variable or exponential offset tells more about the patch than variable CV. 'Apply an exponential offset' tells that the offset cannot be fixed, and will apply to modifying a base level.

Is there such a thing as an exponential offset? That seems worth exploring.
listentoaheartbeat
Doesn't the OP just mean a variable offset that is controlled exponentially, or probably rather logarithmically? As in offset going through voltage divider with a log pot?
cptnal
listentoaheartbeat wrote:
Doesn't the OP just mean a variable offset that is controlled exponentially, or probably rather logarithmically? As in offset going through voltage divider with a log pot?


That's what I thought. Reckoned an offset was static by definition. Anyhoo, just checked my Samara and its offsets have exponential control. On the meter it's 0.75V at 12 o'clock and 5V fully clockwise. Maths and Blinds on the other hand appear to have an even sweep across their +ve range.
pugix
KSS wrote:
pugix wrote:


When we talk about response curves or shape, we're usually taking about how the output of an envelope generator changes over time.

That is a surprising statement to see from you. We talk about many other response curves and shapes which have nothing to do with EGs.



So now we can debate the meaning of the word "usually." Dead Banana

This discussion is absurd. It's ridiculous to define 'traditional' vs some other meanings for the word offset. No wonder people can't understand anything anymore. Words can mean anything you like. And that's my response curve.
pugix
cptnal wrote:
listentoaheartbeat wrote:
Doesn't the OP just mean a variable offset that is controlled exponentially, or probably rather logarithmically? As in offset going through voltage divider with a log pot?


That's what I thought. Reckoned an offset was static by definition. Anyhoo, just checked my Samara and its offsets have exponential control. On the meter it's 0.75V at 12 o'clock and 5V fully clockwise. Maths and Blinds on the other hand appear to have an even sweep across their +ve range.


That is a response curve for a potentiometer. I suppose if you wiggle it fast enough, you get an exponential offset.
KSS
pugix wrote:
So now we can debate the meaning of the word "usually."
It's ridiculous to define 'traditional' vs some other meanings for the word offset.

No, we're not debating the word "usually". And the meaning of offset has been agreed to from the start. But when words are added to the word offset, the meaning changes. Just like shape, envelope shape and wave shape. Or response curve, filter response curve and amplifier response curve.

Or have adjectives and adverbs lost their meaning? That would be 'absurd'? No words are being changed to "mean anything you like". Words still mean what they mean. Multiple words can and do mean something different used together than when used alone. Nothing absurd about that.

Quote:
And that's my response curve.

That's pretty good. I like it. fixed adjverb typo
KSS
Is bias allowed to change over time? Not being funny.
Asking if this word which is not indexed in Strange, but means something similar to offset would be more appropriate to describe a changing control voltage used to effect a change in signal base level? Are bias voltages also expected to be fixed?

How is bias the same or different from offset?
dooj88
listentoaheartbeat wrote:
Doesn't the OP just mean a variable offset that is controlled exponentially, or probably rather logarithmically? As in offset going through voltage divider with a log pot?


yes, pretty much this. (though i have to admit i'm not sure what the voltage divider would do)

i'm not sure using an exponential vca to apply an offset would have the same effect.. it seems like it would, but the pot is still linear.. very frustrating lol i really need to get in front of my modular to mess about with the ideas here

but for clarification, here's what i was originally asking.. blue is obviously the normal response. and by "voltage" i mean voltage output.

Dave Peck
A-ha. So what you are really looking for is a way to CONVERT a linear response from a variable CV source (not an offset) to an exponential response. This type of linear response variable CV source could be something like a triangle wave LFO, a linear manual potentiometer controlling a DC voltage level, or a linear envelope generator.

One easy way to do that is to connect a positive DC voltage (could be +5VDC, could be +10V DC, whatever is the max your VCAs will handle) to the SIGNAL input of a VCA, and then connect your variable linear response CV source to the EXPONENTIAL CONTROL input of that VCA. (Or, if your VCA just has one CV input and uses a switch to select linear or exponential CV response, set the switch to exponential).

Now the output of the VCA will be moving up and down along with the movements of the original variable linear CV source, but it will be converted to exponential curves instead of linear ramps.
KSS
Dave Peck wrote:
A-ha. So what you are really looking for is a way to CONVERT a linear response from a variable CV source (not an offset) to an exponential response.

Yes. As my very first reply said. But converting is not a requirement for the desired result. Using the audio mixer of my first reply will already make the conversion when fed with a fixed dc source. Or mskala's similar use of his own module described above. Both you and Richard seem to require offset be a noun, when it is perfectly ok to use it as a verb. The fixed thing offset and the action of an offset on a patch are both valid uses.
Restating the OP's question as originally understood and now verified by his graph could be, How do I exponentially apply a control voltage to a point or several points in my patch to effect an offset at those points. The macro knob of his OP.

Dave Peck wrote:
One easy way to do that is to connect a positive DC voltage (could be +5VDC, could be +10V DC, whatever is the max your VCAs will handle) to the SIGNAL input of a VCA, and then connect your variable linear response CV source to the EXPONENTIAL CONTROL input of that VCA. (Or, if your VCA just has one CV input and uses a switch to select linear or exponential CV response, set the switch to exponential).

Yes. Again you are saying the same thing as the first sentence of my first reply. Thank you for expanding the details of the patch left out before.

Dave Peck wrote:
Now the output of the VCA will be moving up and down along with the movements of the original variable linear CV source, but it will be converted to exponential curves instead of linear ramps.

But it doesn't have to be a linear CV or an expo VCA if it is used with a CV generator like an EG with already expo'd output or the Audio taper pot in a mixer fed with fixed voltage. Expo VCA with linear CV or linear VCA with expo CV both work.

Whether OP starts with variable linear CV processed to become expo or with variable expo CV directly, the placement of this variable voltage at a point in the patch where it effects an offset completes the answer to the question stated in the thread title.

The two sides seen here about a "fixed" offset definition may be brought together by seeing that once any of these solutions is set up, the divide between the two sides is how often the knob is moved. It can be set once and left fixed. Or it may be changed several times and left fixed at each point in time. Or it may be changed even more often. Carrying this to the point of becoming a variable exponentially applied CV to an offset. Which is what the OP asked about.

Once that is understood, automation like an EG or your triangle LFO can be used to remove or augment the manual knob.
KSS
dooj88 wrote:
yes, pretty much this. (though i have to admit i'm not sure what the voltage divider would do)

He may be describing the use of a resistor or two with a linear pot to make it behave as an Audio tapered pot. Intellijel and others do this with a switch on some of their modules to make them suitable for both audio and cv mixing.

Quote:
i'm not sure using an exponential vca to apply an offset would have the same effect.. it seems like it would, but the pot is still linear..

It may help to see your question as two questions. One is making a conversion from the blue line in your plot to the red line. The second is using that now variable expo CV at the points in your patch where you want an exponentially increasing or decreasing CV.
You called that an offset. Your plot X axis label suggests you may have meant turning the knob and getting an output which is "offset" from the input? A different amount of change in the output compared to the input? Or you may have meant the generally understood offset in synths where a fixed voltage is added to a signal to move it to higher or lower average voltage. two sides of the same thing. One is a source. The other is its application. Replies in this thread show different opinions about correct word use.

Whether you meant the offset action of setting or moving a signal base level or not, you have a knob function which gives more change at one end of the travel than the other in line with your plot. How you use that voltage will determine what it's called beyond just saying CV.

In Dave Peck's patch description the VCA makes the change between the blue and red lines of your plot. mskala and my reply tell how to do it without a VCA. Most replies have included ways to replace the manual knob with CV. Using an LFO to give a repeating behavior once something has made the change from blue to red, or an EG which could be used to both change from blue to red and automate at the same time.
Dave Peck
KSS wrote:
Dave Peck wrote:
A-ha. So what you are really looking for is a way to CONVERT a linear response from a variable CV source (not an offset) to an exponential response.

Yes. As my very first reply said. But converting is not a requirement for the desired result.


My reply is based on the illustration in the OP's comment just above my reply. He's starting with a CV source that has a linear response curve (blue line) and wants to convert it to an exponential response curve (red line).
listentoaheartbeat
I don't think this is what the OP wants. My understanding is that it's just an offset, and the voltage level is set by a log potentiometer instead of a linear one.
Dave Peck
Then either the VCA method I describe or the methods KSS describes would work.
mt3
The variety of interpretations were insightful.
Can anyone recommend the best AC offset utility module for gray area synthesis?
KSS
Dave Peck wrote:
My reply is based on the illustration in the OP's comment just above my reply. He's starting with a CV source that has a linear response curve (blue line) and wants to convert it to an exponential response curve (red line).

Yes. Apreciate your posts in the thread!

I was remembering his Blinds and master Macro knob reference in the OP. Suggesting that he may be content with a knob only based answer.
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