RE: Input and Biquad/QuadBiquad.h and Source...

silver2row am I allowed to use more than one boot setup class in the source?

you can only have one setup() function in a project.

silver2row I looked up the math_neon.h file and there is nothing in it on the docs. Is that on purpose?

there is not much to know about it. It contains fast implementations of some of the math functions available in the standard C library. See, e.g.: https://github.com/BelaPlatform/Bela/wiki/Fast-math-functions, or The Source https://github.com/giuliomoro/math-neon.

silver2row Anyway, do I need to make the bool class in .cpp file aware of my interactions/source within render?

I have no idea what this means.

The full file would look like this:

#include <Bela.h>
#include <libraries/math_neon/math_neon.h>

bool setup(BelaContext *context, void *userData)
{
	return true;
}

void render(BelaContext *context, void *userData)
{
	for(unsigned int n = 0; n < context->audioFrames; ++n)
	{
		for(unsigned int c = 0; c < context->audioInChannels && c < context->audioOutChannels; ++c)
		{
			float gain = 1;
			float in = audioRead(context, n, c);
			float out =  tanhf_neon(in * gain); // using tanh for distortion. Experiment with other functions here
			audioWrite(context, n, c, out);
		}
	}
}

void cleanup(BelaContext *context, void *userData)
{}

I'm curious if you want distortion or a filter sound? Or maybe some of both?

To be clear on terms, "distortion" is usually taken to mean a mathematically nonlinear function that creates harmonics that aren't naturally in the source material.

A filter can selectively make certain frequency components more or less audible (like filterbanks or audio EQ).

Modulated filters can create a form of distortion (like frequency shifting) but we don't often call it distortion since this term is often reserved primarily for waveshaping functions.

Maybe some more explanation for what type of effect you want to perform on the violin somebody can give some specific help. Perhaps the Biquad is the thing you want and you only need some ideas to make this change the sound of the violin in a way you can easily hear.

Maybe you want some distortion like suggested by @giuliomoro where you clip the signal and make it sound more like electric guitar.

For example, I have coded a variety of sound effects which can be implemented on Bela that somebody could use for many fun experiments with a violin. These aren't simple enough for me to recommend them as examples for learning how to use Bela. The examples provided by the Bela team are better for learning because they are short and focus on one thing at a time.

https://github.com/transmogrifox/transmogriFX_bela

Everything works as-is, but you need to have something connected to the Analog Inputs to adjust levels or you might get settings stuck in very strange positions...and you need switches on digital inputs.

as far as i get it, you want to have this violin open to the public, or at least have it played by people who don't normally play the violin? nice.
so i understand that you would prefer some sort of 'different', 'unexpected' or 'surprising' sound to come out of the speaker, instead of just a badly played violin. hah.

and while trying out all the examples may be a good starting point, i have to agree with @[deleted] and @[deleted] that this conversation would become easier once you decide what you want to do with the sound to make it surprising.
you could have distortion, but only on the lower notes. you could have the higher notes be chopped up with a tremolo and disappear into an echo. or maybe you want to trigger Winston Churchill speech samples and speed them up as the violin gets louder?

people here are more than willing to help you get the results you want - but it's kind of hard to help you if you don't know what you want to achieve.

(that said, i can only help you if you choose to go with Pd - my C++ is still at kindergarten level.)

silver2row Enjoy the Faire!

silver2row
The vocoder has the best instructions. If you make the connections as diagrammed on the github README.md then the vocoder will work. You will need a microphone preamp for the ADC CH1 connection
https://github.com/transmogrifox/Bela_Misc/tree/master/vocoder

The "klingon tone" will also work without external connections because the defaults are set to something that will change the sound, and quick review of the code shows it starts in an active state:
https://github.com/transmogrifox/Bela_Misc/tree/master/klingon_tone
^You can do more with knobs connected, but it will do something audibly different without.

The sample/hold modulator, ADSR and state variable filter require more understanding of Bela and the code. The TransmogriFX repo ( https://github.com/transmogrifox/transmogriFX_bela/tree/master/src ) works as a complete system but it requires a combination of correct hardware connections and an understanding of what the hardware inputs do in the code -- neither of which are documented yet, so you have to study the code and experiment to figure out my particular way of doing things to make it work.

ryjobil quick review of the code shows it starts in an active state

i was under the impression that the default was 'bypass = true'.
i should think that it therefore starts in bypass?

Remork i was under the impression that the default was 'bypass = true'.
i should think that it therefore starts in bypass?

While it is true that make_klingon(...) will create a Klingon Tone initialized to bypass state, the specific sketch referenced sets it to active state when you start the sketch.

See render.cpp, in function setup(...)

    //Bypass is the least intuitive function:
    // If second argument is true, it forces bypass state.
    // If second argument is false, it toggles bypass state.
    // The second call below is all that is needed after make_klingon(), since the constructor function
    // sets bypass state to true.  A call to kot_set_bypass(kot, false) would then toggle to active-state
    // since it is already initialized to bypass state (true).
    // However for clarity in the example it is explicitly set to true, then toggled to demonstrate the normal sequence when
    // the current bypass state is unknown.
    kot_set_bypass(kot, true);
    kot_set_bypass(kot, false);

Notice I fixed the comment here, but haven't pushed a fix to the comment in the code, so you will see a discrepancy if you read this section of the code before I get around to fixing it.