Biramp

Overview

Produces an up-and-down ramp signal from an input phasor ramp signal. Things like this are useful for creating quick time-synced LFO signals. Because it ramps down to 0, it won't clip.

A few flavors of biramp will be created: a stateless version with position control, a stateful version with position that only updates at the beginnig of the phasor, and a stateful version with no position contorl that inverts the direction of the phasor at the beginning of each phase.

Tangled Files

Tangles into biramp.c and biramp.h.

#ifndef SK_BIRAMP_H
#define SK_BIRAMP_H

#ifndef SKFLT
#define SKFLT float
#endif

<<funcdefs>>
#endif

#define SK_BIRAMP_PRIV
#include "biramp.h"
<<funcs>>

Version 1: Stateless

The stateless version of biramp is called sk_biramp_stateless.

SKFLT sk_biramp_stateless(SKFLT phs, SKFLT pos);

The stateless version needs only the input phasor signal and split position (expected to be a normalized value).

When the phasor is less than the position, the output is phasor/position.

When the phasor is greater than or equal to the position, the output is 1 - phasor/1 - position.

The position cannot be 0 or 1 exactly. Instead of throwing an error, these will just return themselves.

SKFLT sk_biramp_stateless(SKFLT phs, SKFLT pos)
{
    SKFLT out;
    out = 0;

    if (pos == 0 || pos == 1) return pos;

    if (phs < pos) out = phs / pos;
    else out = (1 - phs) / (1 - pos);

    return out;
}

Version 2: Stateful

The function sk_biramp_stateful is a variation of the stateless biramp with some managed internal state.

SKFLT sk_biramp_stateful(SKFLT phs, SKFLT pos,
                         SKFLT *lphs, SKFLT *lpos);

The stateful version of this functionality can be used so that the position only updates when the phasor resets back to zero. To do this, two additional pointer values are given: the previous phase, and the used cached position parameter.

This will use the cached position value instead of the immediation position value to compute the biramp. The cached value will update itself if it is less than 0, or if it finds the phasor has reset. The phasor resets when the last phasor value is greater than the current phasor value.

The cached phasor value is updated here as well.

SKFLT sk_biramp_stateful(SKFLT phs, SKFLT pos,
                         SKFLT *lphs, SKFLT *lpos)
{
    SKFLT out;
    out = 0;

    if (*lphs > phs || *lpos < 0) {
        *lpos = pos;
    }

    out = sk_biramp_stateless(phs, *lpos);

    *lphs = phs;
    return out;
}

Version 3: Flipper

The final variation, called a flipper, will produce a phasor signal whose direction is flipped when the phase is reset. The stateful variables here include the cached phasor signal from the previous signal, and an integer storing the direction. When the direction is 0, it is normal. Non-zero is a flip.

The direction state is updated on a phase reset, when the cached phasor is greater than the current phasor.

It's important that the cached last phase value is stored pre-flipped. That way, the phasor consistently stays in one direction and makes the reset checker very straight-forward.

SKFLT sk_biramp_flipper(SKFLT phs, SKFLT *lphs, int *flipit);

SKFLT sk_biramp_flipper(SKFLT phs, SKFLT *lphs, int *flipit)
{
    SKFLT out;
    out = 0;

    if (*lphs > phs) {
        (*flipit) =  ~(*flipit);
    }

    out = phs;
    *lphs = phs;

    if (*flipit) out = 1 - out;

    return out;
}