DIY IR+mic pedal: Axoloti

[Cuki79]

Hi everyone,

here is my latest project: a DIY pedal for solo performer.
* Guitar FX:
- 1024 pts IR convolution (Fishman Aura, Tonedexter like: see my previous threads)
- Blend pot for IR
- Full Parametric + high pass filters
- Reverb
* Mic input:
- 12V Phantom power
- 60dB quality analog gain
- High pass filter
- 2 Full parametrics
- High shelf filter
- Reverb
* 3 x standard Li-ion Battery operation

Non tested yet: Compressor, Mic analog preamp + phantom power, battery operation

Irrealistic: Looper (all the above features take 90% of the processing power. IR taking the most of it)

Realistic: Stompbox, maybe auto Stompbox function with a sequencer

The platform is the axoloti a 65€ (wo VAT) board that uses similar (slightly more powerfull) chip than the AMT CP-100 cab pedal. It does not need programming skills... You just wire the FXs. (It's meant for synth, sequencing and FXs)

Here is my axoloti


Here is the current program (it's working!!!)


So now, what's left to be done is the analog board to provide phantom power
Here is a prototype of battery powered analog mic input preamp with phantom power. This box could power the AMT CP-100 IR pedal. The goal is to replace the AMT CP-100 IR pedal by the axoloti.



One amazing axoloti features is the ability to add controls. There are commercial boards that fits on it (see picture)


I will try to make my own board with XLR input, a high impedance analog input and programmable pots. Note that wireless midi control with a smartphone is also possible!!!

I am so excited that the FX already works.

Cuki

[Uncle Pauhana]

This looks fascinating and I look forward to your further experiments with Axoloti.

… But I admit that it makes me crazy that the creator of this device seems to have misread the Nahuatl name for the Mexican salamander, and named it Axoloti instead of Axolotl.

.

[wood nacho]

Super cool! Keep us updated.

[martingitdave]

Cuki,

Can the IR be longer than 1024 pts?
Do you have to have a condenser mic? Why not dynamic and omit the phantom power?

[Peter Z]

That is really impressive, Cuki!

[BT55]

Very interesting project. How hard is the programming and what resources are you using?

[rschultz]

That’s so freakin’ cool. Once you figure it out, sell me one as a kit👍

[Cuki79]

Originally Posted by martingitdave

Cuki,

Can the IR be longer than 1024 pts?
Do you have to have a condenser mic? Why not dynamic and omit the phantom power?

You can add couple hundreds, but then the convolution module would not allow you to go up. The required computer power increases exponentially with the number of points. But for me 1024 pts is enough. I like my tone to be "dry". I'll try to post a demo when I have time.

The condenser mic is a must for me. I have tried many dynamic mic and I still love my SM58 but as soon as I use the Beta 87a... I stick to it.

Note that the project could be much simplier if one would not need high input impedance for the guitar and quality gain. The axoloti provides up to 55dB digitally controlled analog gain.

Input impedance with respect to gain is:

-12 dB gain -> 84.5kΩ
0 dB gain -> 53kΩ
35.25 dB gain -> 2kΩ

Anyway the fun is to make the secondary board with a nice analog electronics and physical controls.

Note that 12v phantom power only requires few resistors and capacitors and is not dangerous so it's an almost "free" feature.

[Cuki79]

Originally Posted by BT55

Very interesting project. How hard is the programming and what resources are you using?

The axoloti comes with a free software. You don't need to know how to program.

The software enables you to make a "patcher" (which is bacically a signal chain) using "objects" which are for example (fx, EQ, compressors, oscillators, inputs/outputs...)

Many objects are programmed by the original designer and there is a whole community adding new objects to the projects (those people know how to program for real)

To make your own patch, you just add "objects" from a list and then wire them as you would do for a vintage synthetizer.


See for example an old Moog:

Of course, for an average guitarists the name of those objects do not ring any bell. A vintage synth enthousiast would know most of the objects and know what to do with them.

In our case, we only use "objects" that are filters, mixers and FX like reverb, compression... but the axoloti was initially meant to play sequence and generate synth sounds.

The only thing I acutally programmed is the conversion of my IR wav file to a format axoloti can read (a table of integers). The longest part being... finding what was the format and how to include the table... Axoloti is a community thing, when you try a new object, you should clic help and it will open an example. Then you can explore the example and infer how it works.
In this case it was simple, if you want to make some special mod to the FX, now you need some programming skills.

PS: However you need some programming skills to know how to make IR wav files for your guitar. This have been discussed in length in my previous posts/threads.

Cuki

[hess]

Cuki, you have the most interesting and educational posts! Keep ‘em coming.

[Cuki79]

Thanks everyone,

Here is a demo of the Axoloti


The signal chain is:
* Martin HD-28 +TA Amulet > BOSS RC-30 Looper > Axoloti
* Beta 87a > DIY mic preamp (Phantom power) > Axoloti

the output of the axoloti is recorded in mono by a Focusrite 2i2. The sound quality of the video does not enable to hear acurately the reverb parameter tweaking... But it works.

Please use headphones and watch in full screen if you want to see what I do with the mouse:


So the axoloti acts as a 2 channel mixer with IR hosting and high pass/parametric or shelf EQs and reverb.

PS:
* Battery operation: checked. The battery was shared with the mic preamp and no extra noise detected. Sometimes digital FX can dump digital noise on the DC power lines. This is not the case.
* Operation with an amp (JAM150+): checked.

Cuki

[Cuki79]

Similar test with a more recent IR file made with a different recipe. This one is made with a sample pre-selection time & frequency based and a post selection to get rid of the digital artifacts.



Can you hear a difference?

(Note that the "selection" recipe is the secret that is not revealed in the Tonedexter patent: it just says that they make the selection based on what a good IR should be. I have my own recipe but it evolves all the time)
Cuki

[The Kid!]

Great idea! Can’t wait to see this when it’s ready to go!

[Cuki79]

Added some controls for test

1 Pot
1 Switch for "layer"
1 LED



Pot works

The switch is supposed to change the function of the layer
* Trouble 1: Sometimes there is a lag before the pot is actually working with its new function.
* trouble 2: When going from layer 1 to 2, the pot "remembers" its position and automatically encode the previous position: that's bad. Imagine you set your gain of your mic to 3/4 turn and then switch layer to set the guitar gain: and it sets alone to 3/4.

...that's bad

Cuki

[martingitdave]

Some of the digital systems will use an infinity encoder in place of a pot. Is that an option?