Recreate Bitcrusher Module in Scriptnode

Casey Kolb

@Christoph-Hart Running into a slightly weird issue with the custom bitcrusher scriptnode module within CUBE. For some reason the bit rate will create a perpetual fuzzy signal even after the sound has finished.

Here's an example:
https://www.dropbox.com/s/n3ehwtbvx18syii/Scriptnode Bitcrusher generating noise even without input.mov?dl=0

Christoph Hart

@Casey-Kolb If you're modulating the bit crusher it will create varying DC offsets at low bit values. What's in the modulation chain?

Casey Kolb

@Christoph-Hart Just a global modulator LFO.

Casey Kolb

@Christoph-Hart Even without modulation, the bitcrusher node it scriptnode leaves a signal active perpetually if the bit rate is anything below 16. The meters will show signal.

JL.LV

@Casey-Kolb I think thats DC offset, you would need to find a way to supress that. I think you would need something to stop th signal from going below -1 and above +1. I tried doing this with the clip node (by modifying the min/max) but it didnt work

Christoph Hart

@JL-LV No you don't get rid of DC offset by clipping to -1...1. What you need is a high pass filter (DC offset is a signal with the frequency 0Hz, so even a simple one pole high pass set to 20Hz will get rid of this).

Casey Kolb

@Christoph-Hart Great! That works for removing the phantom signal from the meter, but I'm still experiencing this weird static noise in my CUBE project: https://www.dropbox.com/s/n3ehwtbvx18syii/Scriptnode Bitcrusher generating noise even without input.mov?dl=0

Christoph Hart

@Casey-Kolb Hmm, the problem is still the DC offset that the bit crusher introduces.

I've made another bitcrusher as snex_shape node which behaves better when modulating (and there's no DC offset introduced).

The snippet export doesn't work with SNEX nodes yet, so you have to do it manually:

Add a snex_shaper node.
Make sure you have a "SNEX code editor" floating tile somewhere (best place would be a tab in the scripting editor tabs).
Create a new file (call it bitcrush2). Click on the SNEX button. Then you should see the shaper class in the SNEX editor.
Enter the code below and press compile.
Add a parameter and set its range to 4-16 (or whatever bit range you want to support
Use and compile the node like any other.

template <int NumVoices> struct bitcrush2
{
	SNEX_NODE(bitcrush2);
	
	// Implement the Waveshaper here...
	
	float getSample(float input)
	{
		const float invStepSize = Math.pow(2.0f, bitDepth);
		const float stepSize = 1.0f / invStepSize;
			
		if(input > 0.0f)
			return (stepSize * Math.floor(input * invStepSize));
		else
			return (stepSize * Math.ceil(input * invStepSize));
	}
	// These functions are the glue code that call the function above
	template <typename T> void process(T& data)
	{
		for(auto ch: data)
		{
			for(auto& s: data.toChannelData(ch))
			{
				s = getSample(s);
			}
		}
	}
	template <typename T> void processFrame(T& data)
	{
		for(auto& s: data)
			s = getSample(s);
	}
	void reset()
	{
		
	}
	void prepare(PrepareSpecs ps)
	{
		
	}
	
	void setExternalData(const ExternalData& d, int index)
	{
	}
	
	float bitDepth = 16.0f;
	
	template <int P> void setParameter(double v)
	{
		bitDepth = v;

	}
};

Christoph Hart

@Christoph-Hart NVM, I've added this as additional mode to the bit crusher node. You can now choose between DC and Bipolar. I couldn't just change the bit crusher algorithm because it sounds very different, but when you want to modulate the bit depth, the new Bipolar mode is much better because it doesn't create a DC offset that is dependent on the bit depth parameter.

(If you load an existing network, it will complain about a wrong parameter structure, but this is OK in this case).

Casey Kolb

@Christoph-Hart Amazing! Will give this a spin :) Thank you

Casey Kolb

@Christoph-Hart @langermarc19 We're hitting a snag here with the bitcrusher in scriptnode. In the compiled VST plugin, it will output only the left channel when the bitcrusher is active, regardless of the mode, DC or Bipolar, and regardless of the bitrate. It seems to happen in most DAWs, but not in standalone.

We're going to take a look at the node code for the bitcrusher, but any immediate thoughts?

Matt_SF

@Casey-Kolb I won't be of much help, but I built a simple bitcrusher here and it works fine (I recall I'm using the bipolar mode)

blezzbeats

Kinda related: Is there any way to access the in-between sample rates of the bitcrusher effect with an integer or float? To get at the rates between 22-44khZ for example, and not just jump that big notch.

Christoph Hart

@blezzbeats Do you mean the sample and hold module? The bitcrusher allows float bit rates.

blezzbeats

@Christoph-Hart I mean the Degrade processor, the samplerate parameter takes big leaps first. Is there another module that has that option? Where I can decide to set the samplerate to 24504 Hz instead of 24000 Hz for example

orange

@Casey-Kolb Have you tried processing for the L - R channels individually?

float getSampleL(float input)
{
	
}

float getSampleR(float input)
{
	
}


// Process the signal here
template <typename ProcessDataType> void process(ProcessDataType& data)
{
	auto frame = data.toFrameData();
	    
	while(frame.next())
	{
		frame[0] = getSampleL(frame[0]);
		frame[1] = getSampleR(frame[1]);
	}
}

Also I reckon that in the above example, float getSample(float input) is used.

With an extra "s", float getSamples(float input) is working here for both channels.

blezzbeats

@Christoph-Hart Nevermind I misunderstood, sample and hold will do it for me! Didn't realize we were talking ScriptFX so I just learned that. Sorry for cluttering the thread .

langermarc19

@Christoph-Hart where in the codebase is polyphonic_base located? Want to look at how prepare is implemented to see if I can write breakpoints/debug output to find where this is getting reduced to mono. Thanks!

langermarc19

@Christoph-Hart nevermind I found FXNodes_impl and I think that has what I need

Casey Kolb

@Christoph-Hart After a lot of debugging, we realized it's not the bitcrusher node but actually the split node that's creating issues in certain DAWs and only allowing the left channel to pass through. We're using the exact configuration of this dry/wet example, just with the bitcrusher instead of the reverb: https://docs.hise.audio/scriptnode/101/drywet.html

When you add a second chain the split container, it won't properly split the channels and the chain on the right will only output the left channel in certain DAWs, including Cubase and Bitwig. This only seems to happen with the node below.

We've tried removing everything and added every node back until the right channel broke. The instant we added a split container with another chain, one of the chains would stop outputting a right signal. This doesn't happen in standalone, and this only seems to happen with the following configuration. Any ideas for things we could try?

Screen Shot 2022-09-07 at 9.34.51 PM.png

Recreate Bitcrusher Module in Scriptnode

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