Anti-aliased bitcrusher with independent bit depth and sample rate reduction. More...

#include <gin_bitcrusher.h>

Public Member Functions
	BitCrusher (int maxChannels_=2, int maxBlockSize_=4096)

void	setSampleRate (double sr)
	Sets the sample rate.

void	setParams (float bitDepth, float rateHz, bool dirtyMode)
	Sets the parameters.

void	reset ()
	Resets all internal state.

int	getLatencySamples () const
	Latency in samples for the current mode.

void	process (juce::AudioSampleBuffer &buffer)
	Processes a buffer of audio.

Detailed Description

Anti-aliased bitcrusher with independent bit depth and sample rate reduction.

BitCrusher combines two classic lo-fi effects with optional anti-aliasing:

Bit depth reduction quantizes the amplitude of the signal to a reduced number of bits (1 to 16). Quantization is a static nonlinearity that generates harmonics which alias back into the audible range, so the quantizer runs inside a 4x juce::dsp::Oversampling stage - the signal is upsampled, quantized at the oversampled rate, then filtered and decimated back down.

Sample rate reduction resamples the signal to a lower rate (e.g. 500Hz to 48kHz) with a sample & hold driven by a phase accumulator, like a sync'd oscillator. Each hold transition is a step discontinuity which would normally cause fold-back aliasing. Instead of naively holding values, a polyBLEP correction is injected around each discontinuity (across the samples before and after the step, via a one sample delay line), giving a band-limited step that keeps the audible stepped character without the harsh fold-back. The held value is sampled at the exact step instant by linear interpolation of the input.

Signal chain: oversample -> quantize -> decimate -> BLEP sample & hold. The sample & hold runs last, at the project rate, since the BLEP correction band-limits the steps relative to the output Nyquist, and holding after quantization keeps the steps exactly on the bit grid.

Dirty mode bypasses all anti-aliasing (naive quantization and naive hold, zero latency) for the raw aliased sound of a classic bitcrusher.

Key Features:

Bit depth reduction (1 to 16 bits), anti-aliased via 4x oversampling
Sample rate reduction via phase accumulator sample & hold
polyBLEP band-limited steps to suppress fold-back aliasing
Dirty mode toggle for the classic raw aliased character
Smoothed parameter changes
Latency reporting for host compensation

Usage:

BitCrusher crusher;
crusher.setSampleRate (44100.0);
 
// 8 bits, hold at 6kHz, anti-aliased
crusher.setParams (8.0f, 6000.0f, false);
crusher.process (buffer);
 
// raw lo-fi: naive quantization and hold
crusher.setParams (8.0f, 6000.0f, true);
crusher.process (buffer);
 
// report crusher.getLatencySamples() to the host

See also: ValueSmoother, AirWindowsDistortion

Constructor & Destructor Documentation

◆ BitCrusher()

BitCrusher::BitCrusher	(	int	maxChannels_ = `2`,
		int	maxBlockSize_ = `4096`
	)

References setSampleRate(), and ValueSmoother< T >::setTime().

Member Function Documentation

◆ setSampleRate()

void BitCrusher::setSampleRate ( double sr )

Sets the sample rate.

Resets the effect.

References reset(), setParams(), and ValueSmoother< T >::setSampleRate().

Referenced by BitCrusher().

◆ setParams()

void BitCrusher::setParams	(	float	bitDepth,
		float	rateHz,
		bool	dirtyMode
	)

Sets the parameters.

Parameters

bitDepth	Bits of amplitude resolution (1 to 16)
rateHz	Target sample & hold rate in Hz. At or above the project rate the signal passes through unheld.
dirtyMode	true bypasses all anti-aliasing for the classic raw aliased sound

References ValueSmoother< T >::setValue().

Referenced by setSampleRate().