Convert 0 to +10v CV to -5 to +5v

I just got a Flame C3 knob recorder which outputs 0 to +10v offsets (thanks, Paul Normand Lebel for the module, and @M.Fischer for the inspiration). I’m now attempting to map the entire range of the knob to the entire bipolar range of parameters like V/Oct on a Ladder Filter and want a second opinion.

Here’s what I’ve done:

  • Ladder Filter V/Oct
    • Input C3
      • Offset #1 Amt = 1.00
      • Linear VCA #1 gain = 0.280
      • Linear VCA #1 bias = 0.100
      • Offset #2 Amt = -0.400

After lots of fiddling, I landed on this approach, but I don’t really understand it. Could someone more voltage/math-smart than myself offer a better solution/explanation of how this is done?

To follow up, taking those three Units (Offset, VCA, Offset) and encapsulating them inside a Custom Unit reduces the range of the mapped values. Once in a Custom Unit, the knob range covers only a small portion of the entire 10v span, but covers the entire span when used as a chain of individual units.

If anybody has any explanation of this, please, do tell.

To shift a 0V to 10.24V range (represented as 0 to 1 inside the ER-301) to a -5.12V to 5.12V range (aka -0.5 to 0.5) then you just need to offset by -0.5.

However, I am a little confused by your goal. Trying to cover the entire bipolar range of the V/oct control is not necessary (nor possible I think). Your knob recorder gives you a 10 octave range so just choose the root (aka lowest) frequency that should map to 0V using the F0 control and then you have 10 octaves of control above that. Afterwards if you want to shift up or down by up to 3 octaves you can use the semitone offset provided inside the V/oct control.

Oh, right. Wow. I somehow landed on the most convoluted way to do that. Thanks for your patience, @odevices. The semitone offset does the trick along with a Linear VCA inside to scale it down a bit so that the top of the knob range maps precisely.

As for trying to cover the entire range of the V/Oct control, I like this approach because when I drop the value all the way down, it’s effectively a mute. When knobs/offsets are limited, it’s a handy addition.

Im not sure the above answers what I am trying to achieve - so hopefully you can shed some light.

Expert Sleepers FH1 which I am using to control my ER301.

Im using a Behringer BCF2000 which is plugged into the FH1 input and then MIDI fader messages are sent out of the corresponding FH1 outputs into the 301. All good.

However, Id like the CV to mirror my MIDI faders. So when the fader is at the top the assigned value in the 301 is at the top and visa versa. At the moment, the +/- 10V scaling means that I am only getting a small amount of range within the 301 when turning my fader up and down.

Ive had a play with the BCF2000 and made sure it is kicking out full range 0-127 values and as CC messages. Ive tried scaling the ER301 - for example using the gain and bias on a Ladder Filter LPF f0 to increase the levels somewhat but of course the the +/-10V means that the f0 value is still not scaling as I want it to.

So I thought you may have something worth suggesting?

Thanks in advance


To what voltage range does the FH-1 convert the 0-127 CC messages?

I found a jumper which has allowed me to provide 0-10V coming from the FH1.
This has improved the performance somewhat. However with the fader at maximum (kicking out 127) the assigned LPF f0 is going to approx 90% of its maximum value. I have increased the gain on on the LPF f0 to get to this level. With the gain set to default, I am only getting a maximum range of about 30% of the LPF f0 value.

My desire ultimately is to control many aspects of the ER301 with this FH1 and BCF setup.

It sounds like you already succeeded in solving your problem? :thinking:

Actually, after reading this sentence more carefully, I’m even more confused. The default modulation gain on the LPF f0 value is zero so that must mean your are talking about some other gain (a gain setting inside the FH-1?). But then on the other hand you obviously know about the f0 modulation gain because you must be setting it at some point but then why wouldn’t you just keep increasing it until you get the desired range for your fader sweep?

I would like the LPF f0 to go to 100%

I think I understand the problem now…

The Problem

  • You have set the f0 gain to its maximum at 5000x.
  • The ER-301 maps the input range of -10.24V to 10.24V to internal range of -1 to 1.
  • Therefore your f0 is sweeping from 0 to just under 5000Hz.

The Ideal Solution

  • Let the f0 gain go up to 20,000x.
  • I will do this for v0.3 of the firmware. In the meantime…

The Workaround

  • Place a VCA in the modulation chain and set its gain to 4x.
  • Now your modulation signal with sweep from 0 to 4 which after 5000x means f0 sweeps from 0 to 20kHz.

I am referring to the modulation gain which can be added to the CV input along with bias (I am not increasing the bias however). I have increased this modulation gain to 5000 but the result of this sees the f0 only getting about 90% of the way. I would like the f0 value to go to 100% of the way.

I’ve come across this restriction too and yes, this would be great - thank you!!

1 Like