This section describes the single-channel processors provided by sfFDN. These are audio processors that operate on a single channel of audio. They can be used at the beginning of the input gains block, at the end of the output gains block, or they can be combined in a FilterBank object and used as a multi-channel processor.

Processors

Delay: A simple delay line that supports interpolation for fractional delay lengths.
Dattorro Delay: A modulated delay line with blend, feedforward and feedback controls, as described by Jon Dattorro in "Effect Design Part 2: Delay-Line Modulation and Chorus". Vibrato, flanging, chorus, doubling and echo are all obtained from this one processor; see MakeDattorroDelayOptions.
Schroeder Allpass: An allpass filter consisting of a delay line and a feedback and feedforward path. See also SchroederAllpassSection, which implements a group of Schroeder allpass filters placed in series or in parallel.
Time-Varying Schroeder Allpass: An energy-preserving allpass whose gain coefficient can be modulated while its integer delay remains fixed. TimeVaryingSchroederAllpassSection groups stages in series or parallel.
FIR: A finite impulse response filter.
Sparse FIR: A sparse finite impulse response filter that allows for non-uniformly spaced coefficients.
IIR: An infinite impulse response filter implemented as a cascade of biquad sections.
One Pole: A simple one-pole filter.
Allpass: A first-order allpass filter.
Controllable Full-Wave Rectifier: A waveshaper that blends between the input and its full-wave rectification, with first-order antiderivative antialiasing and an optional dc blocker. Generates even harmonics.
Signal-Dependent Fractional Delay: Delays the positive and negative half-wave components of the input by different fractional amounts, distorting the waveform around its zero crossings. A milder alternative to the rectifier.
Ring Modulator: Multiplies the input by a sinusoid, replacing its spectrum with two sidebands.

AudioProcessorChain

The AudioProcessorChain class allows you to chain multiple single-channel processors together. This is useful for creating more complex processing chains without having to create a custom processor class. You can add any of the single-channel processors to the chain, and they will be processed in the order they were added.

Energy-Preserving Time-Varying Allpass

TimeVaryingSchroederAllpass implements the normalized Type V structure from J. Werner, "Energy-Preserving Time-Varying Schroeder Allpass Filters," DAFx-20. For input x, delayed state w, instantaneous gain g, and c = sqrt(1 - g*g), it computes y = c*w - g*x and stores u = c*x + g*w. This orthogonal transform preserves y*y + u*u = x*x + w*w at every sample.

Here, "time-varying" means gain modulation only: the delay is a fixed integer number of samples. Fractional or modulated delay lengths are outside the energy-preservation guarantee. ModulationOptions::frequency is measured in cycles per sample, amplitude is the peak gain deviation, and both must be non-zero. The complete range must satisfy abs(base_gain) + abs(amplitude) < 1. Use SchroederAllpass for a fixed-gain allpass.