curve fitting

[walters]

What is Curve Fitting?


here is a site:
http://archives.math.utk.edu/visual.calculus/0/curve_fit.5/


Parallel resistance changes the "wiper resistance" per shaft rotation?
( curve of resistance versus shaft rotation)

1.) approximate log
2.) approximate reverse log
3.) approximate exponential
4.) approximate square-law pattern

What are the tappering values for each types?

 

[audioguru]

Curve Fitting is a way of changing the voltage-divider action of a linear potentiometer to approximate a logarithmic pot for use as a volume control. You add a resistor to ground at the slider of the pot.

 

[walters]

Thanks for the help

How do i get a exponential curve?

How do i get a square-law pattern curve?

 

[audioguru]

Adding a resistor to the slider of a linear pot only approximates a logarithmic response. I don't know how to make it approximate other curves.
I figure that if you need a log pot then buy one, instead of fiddling with a linear one.

 

[walters]

But how do i get a exponential curve pot ? and a square-law pattern curve pot ? who makes them please?

 

[_3iMaJ]

But how do i get a exponential curve pot ? and a square-law pattern curve pot ? who makes them please?

Least squares is a "best wrong solution" approximation. It minimizes the 2-norm solution. It's best to understand what you're trying to do before doing it.

Least squares is commonly used in matrix algebra when a solution does not exist. A least squares solution is guaranteed to exist so in some cases it is advantageous to use it.

 

[theinfamousbob]

To be a bit more broad, curve fitting is the calculation of a line/parabola/higher degree equation that fits a set of data. Curve fitting can be useful for predicting possible outcomes. For example, I could have data for prices of a certain make of car from the past ten years. On a graph, I would have price on the Y-axis and year on the X-axis. The price for each year would be a point on the graph. Now, let's say I want to find out what the car will roughly cost ten years from now. I use curve fitting (I do it on my graphing calculator (TI-86)) and pick an appropriate curve depending on what the data looks like (this assumes you're famillar with the standard graphs for various equations.) Now, I can fit a line and a second degree equation (largest exponent on a variable is 2) and see which curve fits better (gets closer to more of the points.)

Curve fitting in a nutshell.

 

[audioguru]

But how do i get a exponential curve pot ? and a square-law pattern curve pot ? who makes them please?

I don't know why you would need one and I can't think of an application for one. Therefore they aren't available and you must order one to be custom-made for you or make it yourself.

 

[walters]

my Vox wah wah pedal is design for exp and square curves pots only i need one not linear or log

 

[walters]

someone told me to use a spreadsheet problem to do curve fitting

 

[_3iMaJ]

someone told me to use a spreadsheet problem to do curve fitting

do you even know what you're fitting a curve to?

 

[walters]

how do u find out what curve to use or design it to a circuit?

 

[audioguru]

Walters,
Do you want to play with numbers or do you want to replace the worn-out pot in your wah-wah pedal?

You could also copy or design a new wah-wah circuit that uses an ordinary linear or log pot.

What do you want to do?
:?:

 

[walters]

i want a square root pot curve how do i get it please

 

[audioguru]

Walters,
You get the replacement pot for an old wah-wah pedal from a guy who makes and sells copies of the pedal.

Look in Google for Wah-Wah Pedal. A link has the history and an article all about them.
One guy wanted to get rich by making and selling new wah-wah pedals that sound exactly like the old ones so he tried pots from 8 manufacturers with all the tapers they made. The pots were different so he ordered some custom-made pots that were identical to the original old pots.

The guy who makes copies of the old wah-wah pedals might not sell just a pot. He wants to get rich so he will probably try to sell his extremely expensive entire pedal.

Then if you are rich and want to make and sell wah-wah pedals to become richer, you could order a few thousand custom-made pots yourself. :lol:

Quote:
"The subject of potentiometers also warrants another look. Numerous differently tapered pots found their way into use in the THOMAS/VOX wahs. These included, but were not limited to: Allen Bradley Type J, Allen Bradley Type EJ, Centralab (two different, non-labeled tapers), Clarostat EJ, Clarostat J, Clarostat NP, Ohmite AB, Alpha, ERT, ICAR, and FRT.
The unofficial "right" pot was the ICAR. This unit did not have a standard type taper. Because of this, the effect achieved while using an ICAR pot was unlike that achieved using a more standard (U.S.) pot. The ICAR was pretty much in a class by itself.
Interestingly, Centralab offered a pot in Europe that almost duplicated the ICAR, but apparently, they did not sell it in the U.S.

Since the ICAR pots have been unavailable for years, I've had a number of 100% accurate pots manufactured for my use in my tunable RMC3 wah."

 

[walters]

Thanks for the help

The wah is designed for a square root pattern curve pot

The ICAR is a special taper but reverse log

If u look at the wah design its frequency response is center frequency is doing it by square root so its design for a square root curve pot

Where can i get a square root curve pot?

 

[audioguru]

I designed a slowly dimming and brightening LED circuit that has a square-law so that it matches the logarithmic brightness response of our vision. It could give a voltage output to be used directly, or control the resistance of a FET. Its input is linear.
Maybe an audio expander circuit could also be used.
Maybe a multiplier IC could be used.

 

[walters]

what are u talking about i don't get it?

 

[audioguru]

what are u talking about i don't get it?

I was talking about electronic circuits that can convert an ordinary linear pot to a square-law resistance change.

 

[walters]

convert an ordinary linear pot to a square-law resistance change

How do u do this? what circuit would convert a linear pot to a square law resistance?