start and stop ranges for phase shifting

[markphaser]

how do u set the start and stop ranges for a phase shifting filter?

Most the start and stop ranges are fixed resistors/capacitor network for a phase shift filter or a regular filter

A Wah Wah is a notch filter how can u set the start and stop ranges from low to high? would be that feedback back capacitor called the vocal cap.

But each phase shift filter DOD,Boss,maestro,EH,MXR has start and stop frequency from high to low

[markphaser]

Does the LFO change the start and stop frequency of the phase filter?

[Mark Hammer]

No.  The "start" and stop" controls determine the two extremes of sweep that the LFO is permitted to take.  Really, they should be labelled "lowest sweep point" and "highest sweep point".

In SOME circuits, such as the E-H Microsynth, the sweep really does "start" from somewhere, and "end" somewhere.  In most instances, though, the LFO simply remains on, cycling up and down, at whatever rate it is set to, and with whatever output amplitude the LFO circuit produces at that supply voltage.  The controls you are interested in would adjust the impact of the LFO by:
a) adding some sort of DC offset voltage to the AC waveform so that it "started" at a higher or lower DC voltage
b) attenuating the AC voltage of the LFO output so that the peak of the LFO is some particular amplitude above the DC offset.

It is like saying "I will give you anywhere between $1 and $500 above whatever tips you are able to make this week."  If the fixed amount is closer to $1 and there aren't many tips, then the two don't add up to much.  If I add $10 but you make $1200 in tips, then the $10 "offset" has little impact.

[markphaser]

Thanks alot Mark Hammer for the information

How do u set the "lowest sweep point" and "highest sweep point" in a LFO circuit? how can i have a "lowest sweep point" variable parameter(pot) and a "highest sweep point" variable parameter(pot)

Most LFO circuit only have a rate/speed and a depth and i can't set the "lowest sweep point" and "highest sweep point" its fixed

Envelope followers replace the LFO , envelope followers can have a "lowest sweep point" and "highest sweep point" to sweep the frequencys of a filter or phase filter what sets the "lowest sweep point" and "highest sweep point" in a envelope follower please?

[Seljer]

it depends on many things

the range of your LFO (some LFO's have a depth control and other biasing and such things to control it)
the range of the things you are using to interconnect the LFO and the phase shifts (the min/max resistance of your LDRs or JFEts or whatever else you're using)
the other capactors and resistors in the phase stages

[Mark Hammer]

Suppose your LFO produces a triangle wave whose amplitude is 3v, peak-to-peak.  Now also suppose the circuit works off a 9v supply, and that the "control element" the LFO is controlling can be influenced by voltages as different as 1.5v up to 6v.  That is a 4.5 volt range of possible voltages you could feed it.  If you combine a fixed voltage source (of up to no more than 1.5v), and the LFO output, then you can sum the two voltage sources together, so you could get a combined output that went from 1.5v to 4.5v (full LFO, no DC offset) up to 3-6v (full LFO, plus 1.5v DC offset).  Look at the schematics of 4-knob flangers like the Boss BF-2 which use this.

Now, the LFO output can often be fairly large amplitude, and the user of the pedal may wish the "start point" to be up fairly high in the range, so what many manufacturers do is use the Depth/Width control as a sort of pan control.  You can see this in the BF-2 and the A/DA flanger.  If, for example, the LFO could sweep over a 7v range, there would be very little DC offset that could be added before you simply ran out of control (you can't expect to add a 5v offset to a 7v LFO output when using a 9v battery).  So, the pedals I mentioned allow for more DC offset when the LFO depth is reduced.  In effect the Depth control determines how much of the DC offset (Manual control) you want, versus how much of the LFO you want.  The more you want of one, the less you can have of the other.  In that way, the circuit is automatically adjusted so that the LFO+DC sum will never be higher than is technically possible, or advisable for the LDR/FET/clock/OTA you are controlling.

[markphaser]

Thanks Mark Hammer again for the information

Does the DC offset sets the"lowest sweep point" and "highest sweep point"?

Why does the LFO output need DC offset voltage?

The depth parameter on most LFO looks like to me a LFO master volume not a adjustable "lowest sweep point" and "highest sweep point"
parameter trim pots

depth control example:
LFO depth at 3 would be like 1volt peak to peak lets just say
LFO depth at 5 would be like 2 volts peak to peak lets just say
LFO depth at 10 would be like 5 volts peak to peak

The depth is just change the Peak to Peak voltage or amplitude not the "lowest sweep point" and "highest sweep point" u know what i mean?

THe DC offset parameter: is shift up or down the zero crossing point (starting point)

example DC offset paramter:
LFO depth at 3 would be like 1volt peak to peak with DC offset of 1 volt
LFO depth at 5 would be like 2 volts peak to peak with DC offset of 1 volt
LFO depth at 10 would be like 5 volts peak to peak with DC offset of 1 volt

LFO depth at 3 would be like 1volt peak to peak with DC offset of 2 volts
LFO depth at 5 would be like 2 volts peak to peak with DC offset of 2 volts
LFO depth at 10 would be like 5 volts peak to peak with DC offset of 2 volts

LFO depth at 3 would be like 1volt peak to peak with DC offset of 3 volts
LFO depth at 5 would be like 2 volts peak to peak with DC offset of 3 volts
LFO depth at 10 would be like 5 volts peak to peak with DC offset of 3 volts

If any more DC offset with cause LFO Clipping going past or over the power supply rail voltage

What is the DC offset changing?
What does the DC offset do to the control elements(LDR,Lamp,LED,OTA)

If DC offset is set at zero volts the swing of the LFO output is going to be the "same peak to peak volts" where ever u set the depth parameter at it just shifts it up or down but the voltage output is still the same unless u ADD them like superimposing DC volts with AC voltages to equal the rails of your power supply, but still the output of the LFO depth peak to peak voltages is going to be the same swing with zero DC offset or 1,2,3volts DC offset unless the DC offset changes the "STARTING" point for the "lowest sweep point" and "highest sweep point"

DC offset voltage: sets the ""starting point"" in a steady constant voltage not phase or time interval for the "lowest sweep point" and the "highest sweep point"? the DC offset is not changing or setting the "lowest sweep point" and the "highest sweep point" its just shifting up or down the "starting point" on which the "lowest sweep point" and the "highest sweep point" are doing to be superimposing sitting on top of.

Most Boss,MXR,DOD chorus,phaser,flanger LFOs are mostly around 10hz to 15hz?

So the "lowest sweep point" and "highest sweep point" of a 10hz LFO would be?
The "lowest sweep point" and "highest sweep point" of a 15hz LFO would be?

The "lowest sweep point" and "highest sweep point" of a 10hz LFO with 1 volt of DC offset would be?
The "lowest sweep point" and "highest sweep point" of a 10hz LFO with 2 volts of DC offset would be?
The "lowest sweep point" and "highest sweep point" of a 10hz LFO with 3 volts of DC offset would be?

The "lowest sweep point" and "highest sweep point" of a 15hz LFO with 1 volt of DC offset would be?
The "lowest sweep point" and "highest sweep point" of a 15hz LFO with 2 volts of DC offset would be?
The "lowest sweep point" and "highest sweep point" of a 15hz LFO with 3 volts of DC offset would be?

On sweep function generators u can set the "start" and "stop" frequency

The Start and Stop frequency is not the same as the"lowest sweep point" and "highest sweep point"

So the "Start frequency point" and "Stop frequency point" of a 10hz LFO would be?
       a.) Start would be Zero hz to 10hz stop frequency point?
       b.) A constant 10hz not change only the amplitude peak to peak voltage change but
            its still only 10hz at every voltage?
      c.)  Start frequency point is at Zero hz the positive peak voltage is at 10hz and the negative
            peak voltage is at 10hz
      d.) Each instantaneous voltage has a different frequency?


The difference between a LFO VS a sweep function generator
1.) a LFO is a constant set frequency does not change the frequency its FIXED
2.) A sweep function generator each instantaneous voltage has a different frequency?
    its sweeps from 0hz to 10hz or 5hz to 10hz (where ever u set the start and stop frequencys at)
3.) a LFO is FIXED at 10hz but the instantaneous voltages changing but the FIXED frequency
     stays constant
4.) the LFO is sweeping the voltage swing not the frequency of the LFO unless u are automating 
     the LFO speed from slow speed to fast speed thats sweeping frequency
5.) The LFO sweeping the voltages at a FIXED frequency/speed to modulate a filters frequency
     response curve or time constance/phase shift time
6.) If u automate the LFO to sweep from low speed to high speed this = equal what a sweep
     function generator does for setting a start and stop frequency points to sweep at

[markphaser]

A LFO outputs a peak to peak voltage at a FIX frequency
at each instantaneous voltage to changes/modulates the filters frequency response curve , time constants , phase angle

Each instantaneous voltage from the LFO changes the filters frequency **(not the LFO frequency)**
So at each instantaneous voltage value from the LFO change the filters frequency

The frequency Pot on a filters is replaced by a LDR or FET
by change the resistance it changes the frequency of the filter

LFO instantaneous voltage values VS filters instantaneous frequency values chart:

Most people think the LFO is sweeping the frequency of the LFO
like a sweep function generator this causes confussion
Its sweeping the filters frequency from a LFO voltage value

At each LFO voltage value there is a different frequency value from the filter section

[ashcat_lt]

Does the DC offset sets the"lowest sweep point" and "highest sweep point"?

Yes, both.  But actually, no.  It sets the center of the sweep, which thus determines where the highest and lowest will be.

Why does the LFO output need DC offset voltage?

In order to set the center of the sweep higher or lower than the nominal value.

The depth parameter on most LFO looks like to me a LFO master volume not a adjustable "lowest sweep point" and "highest sweep point"
parameter trim pots

The depth parameter is in fact very much like a master volume.  It sets the distance between the lowest and highest sweep point, or if you prefer, the distance between the center and the extremes. 

I don't understand why you would prefer to adjust the "lowest" and "highest" rather than setting a center and a maximum distance of sweep.  Unless you're looking to have an asymetrical wave of some sort, where the distance from center to highest is different from the distance from center to lowest?

There is probably a way to do what you're looking for, but it sounds like a mess to me.  Let's say you could put the LFO into a hold mode for a minute, in order to "preview" your highest/lowest point.  You could then set these by feeding the voltage control input of your filter from your "lowest" knob.  Then flip a switch and set the "highest knob."  Then when you put it back into normal operating mode your circtuitry uses the difference between these voltages to set a virtual "depth" control, and the average of the two to set the center.  No idea how to actually pull this off in a stompbox, maybe somebody around here can help.

I still think it's easier to set a center and depth, which is probably why everybody else uses that method.

[StephenGiles]

Seems to me that what you need is the EH Space Drum envelope generator converted into an LFO.

[oldschoolanalog]

I'm surprised nobody asked this obvious question. What do the start and stop controls on the fabled Mu-Tron flanger actually do?

[markphaser]

Thanks ashcat_lt for your information

StephenGiles 
Seems to me that what you need is the EH Space Drum envelope generator converted into an LFO.

What u mean by this? can u explain more in detail because the envelope generator does have a start and stop frequency points
but how does it work?

the start and stop controls on the fabled Mu-Tron flanger actually do?
        1.) Sweep Start :controls the amount of delay at the start of an LFO sweep
        2.) Sweep Stop :controls the amount of delay at the top of an LFO sweep

I still don't really know what this means the delay at the Start of what im guessing the DC offset voltage
The sweep stop delay at the Top of what?

[markphaser]

I can't really find the Mu-Tron flanger to look at the LFO section does anyone have this?

[R.G.]

It's like shoveling sand against the tide.