Uber Synth is MIDI-controllable layered polyphonic multi-timbral synthesizer that runs on iPhone, iPad, and Silicon Mac computers. The sound engine is a fully polyphonic triple-oscillator cross-modulated frequency modulated (FM) synthesizer. FM is widely regarded as the most efficient way of generating complex “organic” musical sounds.

Uber Synth is divided into groups of modules selected using the control buttons at the top right.

PROG

The “<” and “>” buttons cycle through 32 preset and 32 custom (user programmable) sounds. C/P copies settings of one patch location that you can paste into another. Sounds in the preset sound bank (the first 32 sounds) cannot be changed. There are currently 2 voices per key, which can be changed using the V1/V2 button, and blended with the V1/V2 BLEND rotary control knob. To create your own patch go to a user programmable sound and change any of the oscillators or cross modulation controls. To save the patch tap C/P twice.

At start up for the first time, a file called “patches.xml” is created that contains all of the preset patches. To return to the “factory settings” remove this file from the app’s documents directory using iTunes File sharing. When you restart a new copy will be created. Each time your settings are saved this file is automatically updated. You can also edit this file manually if you like. (Make sure the app is not running so your changes are not over written.)

OSC-A, OSC-B, and OSC-C

xMod uses FM (frequency modulation) synthesis to generate complex sounds from three cross-connected oscillators. Oscillator A sets the fundamental frequency. The reference frequency is A=440 Hz with the TUNE knob straight up. This is the default value. The tuning range for A is 415-465 Hz. (Double tap any control knob to return to the default setting for that control.)

FREQ A shifts the pitch of oscillator A in octave increments up (knob right) or down (knob left). Oscillators B and C run at frequency ratios B:A and C:A relative to A, which are set by the RATIO B:A and RATIO C:A knobs. Although the knobs seem to operate in a continuous manner the frequency ratios are actually quantized to the following values {0, 1/3, 1/2, 2/3, 1, 4/3, 5/3, 2}. This insures the oscillators produce harmonic overtones, which makes it easier to program the synthesizer. Oscillators B and C also have DE-TUNE knobs that add up to ± 0.05 to the frequency ratios to create vibrato, warmth, and non-harmonic overtones.

ATTACK, DECAY, ENVELOPE and GAIN/MOD are controls common to all three oscillators.

GAIN/MOD is the constant output level of the oscillator.

ATTACK and DECAY (really RELEASE in ADSR) are standard envelope generator control parameters.

The envelope generator is triggered when a key is depressed. ATTACK controls the rise time of the sound; DECAY is the rate at which the sound decays after the key is released. ENVELOPE controls the amplitude of the envelope signal, which is added to the output level of the oscillator. When it is straight up there is no change in the output level when a key is pressed. With the knob to the right, the output level increases when a key is depressed and decreases when it is released. With the knob to the left the control signal is inverted, decreasing when a key is depressed and increasing when it is released. Moving the knob further left/right increases the amplitude range.

XMOD

Push buttons A, B, and C route the oscillators to the output. The CROSS-MOD matrix is a 3×3 array of push buttons that cross-connect the three oscillators. For example, the button B~A connects the output of oscillator B with the input of oscillator A so that B modulates A. Oscillator B’s MOD/GAIN controls the modulation index. A~A feeds the output of A back to itself, which is a simple way to generate triangle waveforms, or even noise if the modulation index is high enough. In all there are 2^9 = 512 unique ways to connect the three oscillators.

GLOB

Press GLOB to reveal two modules that provide global controls.

DELAY and DEPTH controls the delay time and depth of a built in reverb unit. BEND changes the pitch of a note when you move your finger left/right after the key is depressed. Try it with stringed instruments. TREMO changes the volume of a note when you move your finger up/down along the key. PORTA slides from note to note. ARPEG generates arpeggios. N.B. TREMOLO and BEND only work with the device keyboard. They cannot be controlled by an external keyboard.

In an adjacent window, KEY SHIFT moves the keyboard up-down. The lowest note is A0 and the highest is B7. KEY SIZE changes the size of the keys. Move either of these sliders to turn off “stuck” notes if they should occur. Touch the window to sustain notes while playing the device keyboard. The sustain feature also works with external MIDI data.

N.B. Turn off multitasking gestures in the settings app when playing the keyboard for best results.

MAP/DYN

Pressing either the MAP or DYN buttons reveal a 2-D map of the different sounds that displays all of the preset sound patches in a 2-D “space” of icons. Sounds that are similar in timbre are near each other. (Each preset and custom sound is represented by a 16-dimensional parameter vector that is projected into the 2-D sound map. The projection algorithm (called non-linear mapping) is not unique and gives somewhat different visualizations each time it is computed at app startup.)

Tap an icon to move to that sound. You can also “smudge” sounds by holding your finger down and moving it around the sound map. The amount of smudging is controlled by the INERTIA knob. Tapping an icon in the sound map gives obtain the original sound.

There are three other ways to blend sounds. Tap SPACE to assign sounds to different notes. Press a key and move your finger in the sound space to the sound you want. Press another key and move your finger to a different location in the sound space. Now play the keys between the two notes and notice how Uber Synth blends the two sounds. You can combine as many sounds in the sound map in this way as you like. When playing watch the sound map change as different sounds are selected and combined depending on the position of the note on the keyboard. Tap RAND to assign random sounds to notes. The variation is controlled by the RANGE knob. CLR clears the assigments.

Another way to blend sounds is to move around the sound space automatically each time a key is pressed. To enable this mode, tap TIME. Each time a key is pressed the current sound which is represented as a point in the sound map moves. RANGE specifies the variation. CHANGE is a randomized amount that moves the point each time you tap a key. INERTIA controls blending between sounds. The V1/V2 BLEND knob controls the mix between the sound of the central icon and the sound of the icon closest to the moving point.

You can also change sounds automatically at a rate controlled by the RATE knob. Tap AUTO for this mode.

Click here to buy Uber Synth on the App Store.