SYNC

A pair of signals with frequencies related by a ratio are useful in musical synthesis. For sub-audio signals, the ratio represent a rhythmic relationship; for audio, it represents a tonal relationship.

If this doesn't immediately click, imagine an instrument playing quarter notes at 120 BPM. It plays two notes per second. An accompanying instrument plays eighth notes, or four notes per second.

Thinking of each new note as one "cycle", the note frequency is 2 notes per second for the first instrument and 4 notes per second for the accompaniment, also understood as a 2/1 frequency ratio. At any tempo, the instrument playing eighth notes will play twice as many notes as the instrument playing quarter notes, and the 2/1 ratio remains.

Extending this, imagine two oscillators with the same 2/1 frequency relationship, but with one at 440Hz and one at 880Hz. The quarter note/eighth note relationship doesn't make sense any more, but another universal musical object emerges: the octave. This is not the only musically relevant interval generated by a ratio of simple integers; the perfect fifth (3/2), perfect fourth (4/3) and any just-intoned interval are all derived in this manner.

Below is a figure of various ratios, their relationships as intervals and rhythmic values, and what a contour at that frequency would look like relative to a timing clock.

The effective space of rhythms and intervals is far from a discrete set of integer ratios (drummers and equal tempered tuning protest), but these idealized frequency relationships can be a solid musical foundation.

SYNC main output borrows the crossfader configuration used by the META and SCANNER modules, but the timing of the crossfade contour is set with a clock input and a ratio.

The SYNC input establishes an external reference frequency. It can accept a wide frequency range, allowing operation as a modulation or sound source. The maximum measurable clock time is about 59 seconds, with measurement quality gradually degrading as the clock frequency exceeds 1khz. SYNC can serve as a master clock source as well; the tempo can be tapped out on the pushbutton.

The X and Y controls pick a ratio from a "scale", arranged as a 2-dimensional grid. The selected ratio and clock input determine the frequency of the contour generator. Each scale has a particular quality, with some suited for tempo-synced modulation, others quantized pitches, and a few designed for all of the above. The arrangement of ratios in each grid is designed to open up the exploration of musical spaces with control voltage signals.

Phase locking ensures consistency when generating tempo-synced signals or audio-rate modulation of the clock. A range of methods are available with increasing correction speed. The modes elicit unique frequency artifacts as they impose phase alignment.

A patch starts with your choice of clock input. From there, you can control ratio selection, crossfader sample and hold behavior, and contour shape. A set of auxillary outputs broadcast related signals to further add musical structure to your patch.

If you haven't yet, take a glance at this introduction of Via's controls, IO, and user interface.

RATIO X and RATIO Y are manual controls for selecting the ratio from the scale grid, setting a position in the X and Y axis.

controls the shape of the crossfade contour. Each WAVE has its own smoothly-adjustable set of contour shapes. They are generally arranged in order of increasing complexity.

RTO X CV is combined with the RATIO X knob to select the current ratio along the X axis.

MOD CV can be set to three destinations, Ratio Y, Phase Offset, or Skew, selected with the MOD parameter.

CV morphs the shape of the crossfader contour. 0 to +5V will span between the position set by the manual control and full-scale morph, and 0 to -5V between the manual control position and minimum morph.

SYNC is the master clock input of the module. Clean square, pulse, or negative-ramping saw waveforms provide the most solid clock. Simple waveforms such as sine, triangle, and positive-ramping saw will give expected results as well, but the phase of the output will be shifted somewhat. The base frequency of complex waveforms won't be extracted; instead the calculated frequency will jump between multiple values. This can create interesting but unpredictable results.

A rising edge at the RESYNC input causes the phase to reset to 0 on the next rising edge.

A X BThe analog output derives its crossfade position between the A and B inputs from the contour generator.

is a reconfigurable logic output, selected by holding shift and tapping S+H. It is either high during the "attack" part of the contour and low during the "release" part, or it is high while moving towards B and low while moving towards A, tracking the changes in direction of a complex waveform. The logic high level between 4.5V and 5V

is a reconfigurable signal output, selected by holding shift and tapping MOD. It can be a triangle, or it can be a direct output from the contour generator. The output range is -5.3V to 5.3V

on the expander produces a trigger when the frequency ratio changes. The length of the trigger is the gate length of the input clock. This signals a change in pitch due to a changing ratio if the contour generator is oscillating at audio rates.

When a touch sensor is pressed, the LEDs show the mode of the corresponding parameter.

The white LEDs connected to the A and B inputs are illuminated whenever the sample and hold on that channel is holding a value. The LED connected to the main logic output is illuminated when the logic level is high, and the LED connected to the MOD CV input gives information about the MOD mode: constantly illuminated when in Phase Offset mode, off when in skew mode, and in Y Modulation mode it blinks each time it crosses into an adjacent row.

The RGB display shows a hue corresponding to the current scale. Each group has a unique base color, and each scale in the group shifts the hue displayed. The display is off when the contour generator is at A, and follows the contour in intensity as it moves closer to B.

The red/green LED above it shows the state of the analog output. It is off at 0V and becomes brighter green with positive voltages, and brighter red with negative voltages.

A SCALE is a two dimensional grid of frequency ratios. Ratios are selected from the grid using the X RATIO and Y RATIO controls and corresponding CVs. An example scale could be visualized as follows:

In case you were wondering, "phase" and "frequency" are related but distinct characteristics of an oscillating signal. As shown in the following figure, "frequency" refers to how fast a signal is oscillating (how many cycles per second). "Phase" refers to how much of a cylce has been completed at a given instant (the top hump of a sine wave is 90 degrees along the way towards a full 360 degree oscillation).

Now that you have seen what phase alignemnt looks like, know that SYNC will adjust its crossfade contour until it has come back into alignment the clock input after a ratio or clock frequency change. There are four possible sync settings:

1. Slow
2. Medium
3. Fast
4. Instantaneous

Each mode imparts a type of artifact when phase aligning. If you want to smooth out glitches in the phase locking behavior and don't mind a gradual glide into aligment, try one of the slower modes. For tightly tempo synced modulations, try one of the faster modes. The following diagram shows the phase correction over time for each of the modes:

MOD routes the the MOD CV (CV2) to one of three possible destinations: (1) the Y dimension in the scale grid, (2) phase offset, or (3) skew of the contour generator. Phase offset and skew accommodate input signals through the audio range, whereas Y modulation is best suited to lower frequency CV signals.

The sample and holds at the analog inputs behave identically for A and B in each of the three modes. In mode (1), they both continuously track the input. In mode (2), they sample the input when the crossfade contour reaches that channel and release the sample when the crossfade contour reaches the other channel. In mode (3), they resample the input every time the crossfade contour reaches the other channel.

Holding SHIFT (GROUP) and tapping SYNC sets a fixed phase offset from the input clock in 90 degree (aka quarter-cycle or quadrature) increments.

The AUX WAVE parameter, toggled by holding SHIFT (GROUP) and tapping WAVE , enables a "global" bank of four broadly useful wavetables that do not change with the GROUP parameter.

The function of the output can be selected by holding SHIFT (GROUP) and tapping S+H.

The function of the output is selected by holding SHIFT(GROUP) and tapping MOD.

The available options are described in the Controls and IO section.

Harmonics

The scales are arranged such that RTO X sets the numerator and RTO Y sets the denominator from a set of ascending integers. As such, a clockwise turn of RTO X increases frequency and a clockwise turn of RTO Y decreases frequency.

1. Integers - Integers up to 8, well suited for general purpose use.

2. Evens - Even integers to 16, also well suited for general use.

3. Mult 3 - The first 8 multiples of 3, which elicits triplets and an unusual overtone/undertone series.

4. Odds - Odd integers through 15, reinforcing odd overtones and creating Bohlen-Pierce intervals.

Arpeggios

RTO X scans through a row of ratios containing harmonically related pitches. RTO Y selects the row from a set of complementary options.

1. Modal Tetrads - Each row contains an arpeggio that walks up the inversions of a seventh chord. The root note of the seed chord progresses up the major scale as RTO Y is turned clockwise.

2. Major to Minor - Arranged similarly to scale 1, the seed chords move from a major mode to a minor mode as RTO Y is turned clockwise.

3. Impressionist - A clockwise turn of RTO X scans up one mode of a scale and then down a complementary mode. RTO Y guides the scales through a harmonic movement according to minimal voice leadings.

4. Bohlen-Pierce - Similar to scale 3, but the scales are modes of the Bohlen-Pierce scale spanning a single tri-tave. B-P scales use only odd integers, so they are complemented by a wavetable based on triangle shapes containing only odd harmonics.

V/Oct Quantization

RTO X scans through a row of pitches scaled to v/oct at the CV input. RTO Y selects the row from a set of related scales.

1. Modes - Each row contains a modal scale such as major, dorian, mixolydian, etc. The rows move through the possible modes as RTO Y is turned clockwise.

2. Tetrads - The quanitzations provide 4 pitches per octaves, with ratios chosen to approximate familiar equal tempered intervals.

3. Harmonic Entropy - The quantization scales favor open intervals at either extreme of the RTO Y control and a denser cluster of more dissonant pitches in the middle of the range.

4. Bohlen-Pierce - Similar to group 2, scale 4, but the scales are extended across the full v/oct span of the CV.

Rhythms

The scales are arranged such that RTO X selects a frequency ratio representing a rhythm relative to the "tempo" provided at the clock input. RTO Y sets the available rhythms. Some scales enforce a phase reset after a certain number of input clock cycles.

1. Rhythmic Harmonics - The ratios are arranged in the fashion of group 1, but the integer set is chosen to create the frequency ratios associated with common rhythms.

2. No Triplets - Similar to scale 1, but without ratios containing a multiple of 3.

3. Triplets - Similar to scale 1, but all multipliers are a multiples of 3.

4. Dotted - Similar to scale 1, but with dotted rhythms.

Audio and Modulation

1. Additive Evens - Mimics a smooth transposition through increasing even harmonics.

2. Ramps - Each slope consists of an increasing number of ramps; existing ramp start and end points stay in place as new ramps are added.
   

3. Bounce - Morph through snapshots of bouncing ball simulation with increasing number of bounces.
   

4. Circular - The shape morphs from a logarithmic-like shape to an exponential-like state. Intermediate shapes have flatted regions between curve slopes.
   

Audio

1. Impulse Train - Impulse waveforms with increasing overtones resembling a filter sweep without resonance.
   

2. Tri to Square - Morph from a triangle to an additive recreation of a square wave.
   

3. Perlin Noise - One dimensional slices from a spatial noise algorithm, increasing the frequency of noise per waveform.
   

4. Synthesized Vowels - Morph through renders of a modeled vocal tract using an impulse train and a filter bank tuned to the resonances of different vowels.
   

Audio

1. Additive Pairs - Emerging pairs of odd overtones.
   

2. Filter Model - A square wave through a modeled transistor-ladder lowpass filter with increasing cutoff frequency.
   

3. FM - Samples from a two-operator FM configuration with increasing modulator frequency.
   

4. Sampled Train Whistles - Morph through waveforms re-synthesized from train whistles.
   

Modulation

1. Symmetric expo/log - A pair of exponential curves transform into a pair of logarithmic curves.
   

2. Asymmetric expo/log - The first half morphs from a bowed out logarithmic curve to a sharp exponential curve. The second half morphs between the same shapes in the other direction.
   

3. Steps - The slopes are stepped, morph adds steps.
   

4. Sequences - Interpolate through a set of 16-step sequences, with 8 steps per slope.
   

Audio and Modulation

1. Odd Triangles - Mimics a triangle wave transposing through increasing odd frequency multipliers.

2. Odd Sines- Mimics a sine wave transposing through increasing odd frequency multipliers.
   

3. Euclidean Ridges - Distribute ridges across the slopes according to the euclidean algorithm and morph through underlying patterns.
   

4. Skip Saw - Impose sawtooth ridges on a triangle wave with an increasing number of ridges.