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bassdude

Midi remote volume controller

11 posts in this topic

G'day,

I was directed here from another forum (http://www.organforum.com/forums/showthread.php?17098-Midi-controlled-analog-volume-pedal-how-to-or-available-anyone). A quick look around tells me I'm way out of my depth as a noob to midi, so I'm bound to mess up terminology & any & all assistance is welcome!

A search for "remote volume" yielded 1 hit utilising a Midibox CV and I don't know if that's the only solution, nor where to start.

Basically I would like to utilise one of an FCB-1010's expression pedals to remotely control volume of an analog signal. I would be hoping for a compact solution that needs at least a midi-in, audio in & out (both 1/4"). A nice to have would be some method of selecting the midi channel in which to receive the continuous controller input.

One solution exists here (http://www.prostage.eu/en/shop/shop_1.html), but I don't have €198 to throw at this solution.

Peter Sharp

Ballarat Australia

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Hi Peter,

Let me see if I can help you find the correct terminology for the solution you seek. As I understand it, the FCB-1010 has an expression pedal that puts out MIDI messages when it is moved. The messages are probably MIDI Continuous Control (CC) messages, probably Volume (CC 7) or Expression (CC 11). You want a device that will receive those MIDI messages and use them to control the volume of an analog signal. The volume control might be by controlling an attenuator (variable resistance) or an amplifier (VCA or voltage controlled amplifier although you really are using MIDI rather than voltage for the control).

I am 99% sure that one or another of the MidiBox projects can do what you want. There is probably another area of this Forum that is more appropriate for your question. In Midification we are trying to go the other way, taking inputs and creating MIDI Messages. So we are primarily focused on the MIDIO128 project. That is not what you want.

One last thing, I assume that what you want to do with the analog signal can be easily accomplished with an audio taper potentiometer and that what you want to is in effect turn the knob on the potentiometer using the MIDI from your pedal. Do you know if that is the case? Knowing that will help to define the analog requirements. I will also point out that almost all electronic organs use an expression pedal that mechanically turns the shaft on an analog taper pot to control the organ volume. Have you considered finding such a pedal from an organ that is being discarded and using that, bypassing MIDI entirely? Slightly more elegant would be to add a mechanical linkage to your FCB-1010 pedal connected to an audio taper pot to control the analog signal directly.

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Thanks Jim,

I don't have access to an organ for scavenging parts, but I guess it's an option. My situation is I have 2 signals from my bass guitar - the raw signal and a midi-fied signal driving a Roland XV-2020 synth. The goal I'm trying to achieve is to be able to operate the FCB-1010's two adjacent expression pedals to control the volume of each signal path either independently or in unison with one foot. The synth chain responds nicely to volume (CC7) commands from the FCB=1010, & I'd like to achieve the same with the raw analog signal using the 2nd expression pedal. Yes, the expression pedals generate CC commands of whatever type it's programmed to send.

I'll have to explore the MidiBox forums to see what's available.

Peter

Edited by bassdude

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Basically I would like to utilise one of an FCB-1010's expression pedals to remotely control volume of an analog signal. I would be hoping for a compact solution that needs at least a midi-in, audio in & out (both 1/4"). A nice to have would be some method of selecting the midi channel in which to receive the continuous controller input.

The Good News:

There is a project here called "MBMixer", based on the PIC core, that can do exactly what you want. The design is tested, the software is here online... I'm too tired to look it up, but Google "MidiBox Mixer" and you'll find it.

The bad news:

The boards have never been produced in any quantity, so you'll have to hand-wire or design your own PCB to make it work. If you choose to hand-wire one, the PGA2311 is available in a DIP package, and will work fine with the software.

In addition to that chip, you will need a Bipolar (plus and minus) 5 volt regulated supply, and you should consider an op-amp input buffer (very simple once you have the supply).

The sound quality is very good, I have been using my mixer daily for years now. My first design was hand wired, the current design uses circuit boards.

A newer revision was made, but never produced or released.

If you decide to go in this direction, I will gladly offer my personal E-Mail address and support you with information along the way.

LyleHaze

edit: after reviewing the light dimmer kit you linked to.. it looks like that kit can convert knobs/foot pedals into MIDI messages, and can also convert MIDI messages into a variable voltage output, but I do not see any circuitry that would provide audio volume controls. Perhaps if you added a VCA for each audio channel, but otherwise I think you'll be missing part of what you asked for.

Edited by lylehaze

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Lyle,

Tom actually said he would supply a completed version of this kit modified to generate a CV of 0-5V corresponding to the full CC range of the midi expression pedal. He said it also needs a VCA and suggested this (http://www.musicfromouterspace.com/analogsynth/DLLVCA001/DLLVCA001.html) as one possibility. It's just a PCB & parts list, which is hopefully relatively inexpensive to fit out.

On another forum this (http://highlyliquid.com/midi-decoders/md24) was offered as a possible solution. It offers 24 outputs as either logic or servo/PWM for a similar price to the offered Miduino CV kit, so it looks like good value. However, I've no idea about converting a pulse signal into a CV, nor do I really need 24 options to choose from - but it could come in handy to have that flexibility available...

If you have an alternative solution to offer for the VCA I've been shown, please contact me :-)

PS. I really know nothing about electronics, besides being able to solder & whatever I've picked up on a few forums just these past few weeks. So all help willingly received.

Peter Sharp

Ballarat Australia

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If you have an alternative solution to offer for the VCA I've been shown, please contact me :-)

Well, yes. As I suggested above.

PGA2311 can be used in the MBMixer

A single PGA chip(or as many as you want) can be connected directly to a PIC core to give

a really high quality volume control in 0.5 dB steps. No PWM, averaging caps or VCAs needed.

All it does need is positive and negative 5 volt supplies, and the software that has been

posted here.

Whatever path you choose, I hope you have fun with it.

LyleHaze

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While it would (I suppose) be overkill, if you wanted to use the newer STM32 based CORE32 rather than the CORE8, you could use Jonathan Farmer's dpot (Digital Potentiometer) driver.

Digital Potentiometers work in a similar way to their analogue counterparts but are controlled by an SPI interface rather than fingers :)

The code is available here and currently supports the MCP41xxx series of dpot IC's. You would probably need a simple op-amp as well as you don't want to feed the audio straight through the dpot.

Obviously no PCB's or indeed software (other than MIOS32 and the dpot driver) exist to achieve this so it is something that you would need to create yourself. I know that Lyle has suggested the MB-Mixer and this is another great solution to the problem with the added benefit that the software has already been written !!!

If you are looking at a DIY solution as a way to save money against a commercial one then I think that you will be disappointed, unless you find a 'kit' that already does exactly what you want, you will probably end up spending more than €198. What DIY gives you is the warm fuzzy feeling that you created it yourself :)

Cheers

Phil

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While it would (I suppose) be overkill, if you wanted to use the newer STM32 based CORE32 rather than the CORE8, you could use Jonathan Farmer's dpot (Digital Potentiometer) driver.

Digital Potentiometers work in a similar way to their analogue counterparts but are controlled by an SPI interface rather than fingers :)

At the risk of going too far off-topic, most digital pots require all connected signals to be between the supply rails of the chip.

In the case of the chips you mentioned, this means the audio signals have to stay between 0 and +5 volts. Since an audio signal is AC, this means you'll have to add a DC offset before the digipot, then block the DC offset afterwards to get back to an AC signal.

This is an often overlooked restriction on analog pots. You can find all of this in the device datasheet.

LyleHaze

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I think those dpot and pga solutions would not allow to sweep the volume while playing, because the output would be steppy.

Building a Midibox CV with an Aout-LC and feeding its voltage to a VCA will allow sweeps and could be way cheaper than €198.

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Thanks all for the input. I think I'm settled on going with Tom Scarff's Miduino midi-CV option. An added advantage for me is that I can play with the Arduino code myself to enhance the midi-out send, as Tom also is happy to supply the source code. I also have a need to add some midi channel multiplexing logic to allow the FCB-1010 expression pedals to control synth volume (or other effects) over multiple channels simultaneously. That will allow me to make the most of the Axon AX100 string splitting capability (ie. separate channel for each bass string) coupled with driving an external synth (the Roland XV-2020). While I'm at it (tinkering with code), I may also add a reverse volume capability/option, so that instead of simultaneous fade & swell of synth & raw bass signals, I can instead also operate the 2 expression pedals in unison to fade out one signal while fading in the other. Sounds like it'll be fun :-)

Peter

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