MIDI Controlled VCA for guitar...

Using Arduino Audio
#1

Started my first Arduino project about a year ago, and bit off way more than I could chew for a first project, then found a commercially available product (BOSS MS-3) that did everything I wanted and more for a very affordable price... So I abandoned the project and went that way..

Good news is I have a lot of parts from that project from which to work with for the one I need to build now...

I need to build a volume control for a dry signal from my guitar, that is controlled with MIDI #CC.. Basically, it will go in between the output of the guitar and the input of the amp, and be controlled via an Expression pedal plugged into my MS-3, sending MIDI data out of the MIDI port on the MS-3..

I have an Arduino UNO and an Arduino Mega.. I also have Mike Cook's book on Arduino Music and Audio Projects... But have only browsed through it..

I'm hoping to find a ready to build project somewhere, that I can just follow instructions plug in the code and see it work (but life rarely works out that easy, does it?)..

Found a sound card schematic in Mike's book, and I guess I could get an Arduino Duo, build the card, add MIDI ports to the Arduino and write/load some code, but I'd have a lot of learning to do that (or would I), and I'd like to finish it sometime in this millennium..

Thing needs to fit in a 1U 19" rack enclosure with other jacks, relays, etc. in it, So I guess the thing should be 1.25" or less in height.. Plenty of room in the other dimensions...

So, where do I start? Any projects out there that will accomplish this (already searched in the audio project hub)?

Or should I build Mike's sound card, add MIDI, and then come back for help programming it all?

Looking for good quality sound, and an analog VCA circuit would work fine for me as well (seems like D/A and A/D conversion is overkill for something like this, but I don't really know)..

So, basically, I need some direction/advice..

Commercial solutions that I found are 'way' expensive (I found 2, one for $230 and another for $300) for what they do...

Thanks,
Mark

#2

PS: I will need to be able to 'mute' the signal via MIDI as well via #PC message..

Thanks,
Mark

#3

Do you want a MIDI controlled Voltage Controlled Amplifier, or a MIDI controlled volume control?

There are examples with digital potentiometers available, and you can even get specialized volume control chips (a quick Google search yielded the MAS6116, for example, but there might be better-suited alternatives for an unamplified mono guitar signal).
Adding MIDI to that shouldn't be too hard.

Pieter

#4

PieterP:
Do you want a MIDI controlled Voltage Controlled Amplifier, or a MIDI controlled volume control?

I'm not sure?? :o

PieterP:
There are examples with digital potentiometers available, and you can even get specialized volume control chips (a quick Google search yielded the MAS6116, for example, but there might be better-suited alternatives for an unamplified mono guitar signal).
Adding MIDI to that shouldn't be too hard.

Pieter

I really have no idea which direction to go.. I have enough of an electronics background (lifelong tinkerer, former electrician, avionics tech in the marines, avionics tech for Magnavox, Garrett AirResearch, etc.) to breadboard and solder (even know how to make circuit boards, or I can use my CNC router for that), but man, when it comes to design I don't even know where to start..

#5

Would something like this work for what I’m trying to do?

The thing uses a circuit board with a pot on it for control, but I’m wondering if an arduino could replace that and then I could control the arduino with MIDI…

It’s impedance matching, voltage supply, grounding, and noise that I have no idea whether this would work or not… Not to mention gain… I’d hate to blow the input circuits of my amp or something…

Digital Stereo Audio Volume Control Board PT2259 Headphone / Audio Amplifier DIY

Thanks,
Mark

#6

I wonder if I could use an inexpensive guitar preamp somehow…

Can an arduino be used to replace a potentiometer on a preamp circuit?

If so, then it would simply be a matter of picking out a transparent preamp, wiring the arduino to where the pot connects, attaching a couple MIDI jacks to the arduino (MIDI IN/THRU), and coming up with some simple code, no?

Or maybe I could mod an old distortion pedal or whatever?

#7

Okay, so a search of arduino digital potentiometer returned a lot of results..

Now I know I could get an old pedal (anything with a volume control that goes from zero sound to max) and replace the pot in it with a digital pot controlled by an arduino..

Would such pots work on the high Z magnetic signal by themselves, or would they inject a bunch of noise or whatever?

Thanks,
Mark

#8

Most guitars use 250k or 500k audio taper pots for volume

So far all of the digital potentiometers I'm finding are either 10k or 100k resistance..

Is 100k enough, or am I missing something? Do I chain 2 or 3 of them in series, and apply the control voltage in parallel?

Or is there a 250k or 500k digi-pot out there somewhere?

None of them list whether they are linear or audio taper.. Can audio taper be done easily via programming?

Thanks,
Mark

#9

Most guitar preamps have an input impedance of close to 1 MΩ, so you'll need a preamp if you want to use one of those digital pots.

The output impedance of effect pedals will probably be lower than the actual pickup, but still.

You could use linear digital pots, but you would lose some resolution at low volume.

Pieter

#10

You probably need a chip that is designed for volume control like this:-

This will need to be connected to the Arduino through its SPI interface. You will need to write code to control it, and then use incoming MIDI messages as input to this code. It should not be difficult but it is not a task for a beginner.

#11

Grumpy_Mike:
You probably need a chip that is designed for volume control like this:-

http://www.ti.com/lit/ds/symlink/pga2311.pdf

This will need to be connected to the Arduino through its SPI interface. You will need to write code to control it, and then use incoming MIDI messages as input to this code. It should not be difficult but it is not a task for a beginner.

Truthfully, I was thinking/hoping that 'someone' had to have run into this need before, and there would be a project out there I could just follow...

But apparently not..

Sounds like I'm gonna get stuck forking out $250-300 just for a simple volume control...

#12

Truthfully, I was thinking/hoping that 'someone' had to have run into this need before, and there would be a project out there I could just follow.
But apparently not.

I haven't searched the internet for you, but if you haven't found any ready built project then I guess no one has put one on line. It is an unusual thing to want to do as most people using MIDI will just use the volume commands in what ever DAW they are using.

Sounds like I'm gonna get stuck forking out $250-300 just for a simple volume control.

As you have discovered a volume control is not simple. It might appear like it is to you, but look at that data sheet I posted, it is anything but simple inside.

#13

This isn’t really what you want, but if you’re willing to sacrifice the need for it to be an Arduino project, you could consider using an Axoloti. I have one on my (guitar) pedalboard that responds to MIDI and does all kinds of things, including CC-controlled volume. It has a graphical programming interface for creating patches from a mountain of provided components (e.g. oscillators, filters, fx, mixers etc.), although you can create your own in C (advanced). The boards are 65 Euros.

#14

gutbag:
This isn't really what you want, but if you're willing to sacrifice the need for it to be an Arduino project, you could consider using an Axoloti. I have one on my (guitar) pedalboard that responds to MIDI and does all kinds of things, including CC-controlled volume. It has a graphical programming interface for creating patches from a mountain of provided components (e.g. oscillators, filters, fx, mixers etc.), although you can create your own in C (advanced). The boards are 65 Euros.

Very Interesting!

Is it transparent sounding as a volume control?

Can the volume curve be adjusted?

What else can it do? FX?

I had woken up this morning deciding it would be cheaper to just find a MFX unit that has 5 pin MIDI I/O, then I could also have MIDI FX to the amp...

This might be the hot ticket.. Looks like it might fit inside my 1U rack too!...

Don't really care how it gets done.. Easy and affordable are the main considerations, after that size... Definitely don't want to spend $200-300 for a simple volume control.. That just seems ridiculous..

Thanks for the heads up!
Mark

#15

@gutbag,

It appears they are out of stock.. Do you know if this is a typical thing, a temporary thing, and how long this condition might last? Are you active in the forums there?

Thanks,
Mark

#16

Very interesting product!
Do note that it has low-impedance line inputs, not instrument inputs. You could use a DI box for your guitar and then plug it into this device.

If they don't have new stock soon, you could relatively easily create your own.
Looking at the schematic, it's basically an I²S ADC/DAC chip and an STM32 as a DSP in between.

You can get the same thing by using a Teensy 3.x, an I²S ADC/DAC chip. Axoloty uses an ADAU1961, but there are many similar chips. Teensy has great audio support, so you can add not only volume control, but also effects, audio over USB, 5-pin DIN MIDI, USB MIDI, etc.
See the Teensy Audio library, programming is going to be relatively simple.

Do note that this is a digital solution, and you'll probably lose some quality, because it's only 16-bit at 44.1kHz (although the ADC/DAC will probably support rate conversions). However, as long as you watch your levels, the low bit depth shouldn't matter, and you probably won't really hear a clear difference anyway.

I think the possibility to implement your own effects far outweighs the audio quality concerns, it could be a lot of fun.

#17

I'm going to keep the Axoloti in mind for future as my Pedalboard is currently based around a GP-10 synth pedal and and MS-3 so it will fit right in (could just plug the thing into one of the MS-3 loops), but I have decided to go with a LINE 6 M5 MFX pedal..

It has a 5 pin MIDI DIN connector, responds to #CC messages to control any parameter in the thing, has the awesome LINE 6 sound quality, and it's only $150.. This way I get a MFX solution on the way to the amp too.. When not using the amp and just going direct to Mixer, I can use the thing in an MS-3 loop to insert it into the existing FX chain....

This is a great solution for me.. Gonna download the manual and 'make sure' it will do what I need and then pull the trigger..

I'll eventually find a purpose for the Arudinos I bought that isn't so 'over my head' for a beginner.. I haven't even looked into a Arduino based security system I was thinking about using it for when I first bought the thing..

All the usual commercially based systems are designed to work with cellular service, and we don't have any here where I live, so I wanted to create something with an autodialer that would contact my neighbors with a prerecorded message, or even have capability to transmit over my HAM radio..

Even if I have to hack into a simply safe somehow (it does have a land line feature that calls to their service as aback up to the cellular) to just do the autodialer/radio part.. It also has no aux contacts I can use not only to trigger an auto dialer but to trigger a 'louder' audio alarm (we all live kinda far apart here, lots of big trees so I'd need something 'loud' like a 120v fire alarm for my neighbors to hear it...

So that will probably be what I try and use these things for, unless I run into another 'emergency situation'..

Thanks,
Mark

#18

Re Axoloti:

Is it transparent sounding as a volume control?

I think so. In my setup, it's always on, so perhaps I've compensated with other settings.

Can the volume curve be adjusted?

Yes, although I haven't done it. There will be several different ways of varying complexity.

What else can it do? FX?

Basic guitar FX. I use delay/chorus/flange and some bitcrusher distortions.

It appears they are out of stock.. Do you know if this is a typical thing, a temporary thing, and how long this condition might last?

It's a one-man operation, and he makes batches from time to time. You could post a message on the forum asking about the next batch if you wanted.

Are you active in the forums there?

Not active, just a browser. Now that I've got it doing what I want, I'm not changing it. I have bursts of work on it (adding new patches as the music demands).

Do note that it has low-impedance line inputs, not instrument inputs.

Yes, I have it between two buffered pedals.

If you do decide to consider it again, you can download the software and get a feel for how much it can do - without the hardware. There's an active community of people developing all kinds of good stuff. Much of it is more to with synthesis than guitar processing, but I've found some useful things that would be very hard to find in an off-the-shelf pedal.

Hope that helps.

#19

gutbag:
Re Axoloti:
If you do decide to consider it again, you can download the software and get a feel for how much it can do - without the hardware. There's an active community of people developing all kinds of good stuff. Much of it is more to with synthesis than guitar processing, but I've found some useful things that would be very hard to find in an off-the-shelf pedal.

Hope that helps.

Pretty sure I will be considering it.. I'm already looking at the Meris Enzo, and some of EHXs synth pedals to augment the GP-10... Those are to be inserted in the MS-3 loops, and the Axoloti will be better suited there too... Gonna leave room for it in the 1U rack box for the second pedalboard..

So can patches be saved and shared?

BTW, Ordered the M5 this afternoon.. I think it is the perfect solution for my need, and half the price of the dedicated solutions..

#20

So can patches be saved and shared?

Yes. You can save the patches in source form from within the GUI. The compiled versions can be saved on the Axoloti's SD card, and the active patch can be changed with a MIDI PC message - although it's a bit tricky. The patch sources can be shared (it's just an XML file).