Press [FUNCTION] repeatedly to advance to screen #4
Press the second red dot on the multi-touch pad to select “VOICE INIT”
Press it once again to answer “YES”

Press [EDIT]
Press [ALGO]
Using the first column in the touch slider area select Algorithm #8

The numbers inside square boxes represent the Carriers (and will be audible); the numbers inside the circles are Modulators (their influence will be applied to the Operator to which it is connected). In this first experiment we will use Operator 2 to modulate Operator 1. 
In this initialized Voice only Operator 1 has any Output LEVEL. Touching the keyboard you will hear a pure sine wave. Sine waves have no harmonics and much like a single “drawbar” on a tone wheel organ, you are hearing just the fundamental tone of the key you have struck.

Shown at left is the output of Carrier Operator 1 (four complete cycles of a sine wave are shown).
Output is set to 100 (0-127).
We describe this tone as pure, whistle-like – it contains no harmonics (no overtones). It is just the Fundamental pitch.

Touch the [FREQ] button
Here you can see the tuning Frequency of the Operators (called the Ratio). All Operators are initially set to sound the Fundamental, 1.00. This means: if you press the key “A3” (A440 – the ‘A’ above middle ‘C’) you will hear a pure sine wave at 440 cycles per second. Harmonics are whole integer multiples of the Fundamental (1.00) – so that when you see a whole number 1.00, 2.00, 3.00, 4.00 etc, you are seeing the harmonic (or overtone) series. And as with frequency values, when you double the integer you go up an octave: 2.00 will be an octave above 1.00; and 4.00 will be an octave above 2.00; and 8.00 will be an octave above 4.00 and so on.

When the Frequency Ratio between Modulator and Carrier is 1:1, that is, they have the same value, this will create a Sawtooth Wave (Sawtooth describes a wave that contains all harmonics).
To hear this we will need to raise the Output Level of the Modulator (Operator 2).

Press [LEVEL]
Using the second column in the touch strip slowly raise the LEVEL of Operator 2. As you raise the LEVEL you will hear a change in timbre – the sound will start to become more complex. The relationship in LEVEL between the Carrier and Modulator affects the brightness of the sound. As you continue to raise the LEVEL of Operator 2, the brighter the timbre. The Sawtooth wave will include all harmonics. This sound is described as bright and buzzy.

Shown at left is the Output of Operator 1 while being modulated by Operator 2 (Modulation Index = 75). As you increase the Output Level of Operator 2 it will further distort the wave shape – it is this disturbance in the wave shape that our ears/brain interpret as richer harmonic content. Again we show four complete cycles of the wave.

Return the LEVEL of Operator 2 to 0.

Now lets set the Ratio of the Modulator to 2.00 and try the same experiment by raising the LEVEL of Operator 2… as you approach about 75 you will hear a very distinct Square Wave timbre. The Modulator:Carrier ratio is 2:1 – this results in generating every other harmonic (odd numbered multiples of the Fundamental). The Square wave will include all the odd number harmonics 3.00, 5.00, 7.00, 9.00 etc. This sound we describe as hollow, woody, reedy. 

Shown at left is the Output of Operator 1 while being modulated by Operator 2 (Modulation Index = 75). As you increase the Output Level of Operator 2 it will distort the wave shape – in this case we see a distinct ‘squaring’ of the wave shape. Again we show four complete cycles of the wave.

Once again return the Level of Operator 2 to 0

Now lets set the Ratio of the Modulator to 3.00 and try the same experiment. Again as you approach about 75 and more, you will hear a very tight, narrow waveform (Pulse wave). And as you can guess, the 4:1 and 5:1 will give ever narrower results – and tighter narrower pulse waves. While the M:C of 2:1 could be used to recreate a Clarinet. The M:C of 4:1 could be used to recreate an Oboe. Both “reedy” sounds but one more nasal than the other.

Learning to use a two Operator stack to build these basic wave shapes (Sawtooth, Square and Pulse) is a good start to sound designing on the reface DX. In the next installment we’ll take a look at these “new” Operators and their ability to Modulate themselves and how this opens some new opportunities for detail. 

If you want to discuss this article or have any questions, go here!

Inspired by the classic DX7 style FM synthesis, the reface DX offers some different wrinkles. Stereo, dual Insertion Effect processing, capacitive touch data entry, and more. The original DX FM required, at minimum, a short stack (2 Operators) to generate a complex waveform. In reface DX each Operator can be made to generate a complex waveform. There are four Operators, each is initially a sine wave generator, but each can be fedback on itself to create more complex waveforms from a single Operator.

Frequency Modulation is basically using the output level of one waveform to modulate or change the output of another. This is accomplished by feeding the output of one oscillator into another. The Modulator is not heard directly, but you do hear its influence on the result from the other oscillator which is called the Carrier. FM, yes like the radio signal FM… Those radio signals are transmitted at frequencies far above what we can hear, DX-style FM takes place with frequencies well within our range of hearing. But it is the same FM.

As musicians, we can better understand this Modulator:Carrier relationship by thinking musically. Imagine a violinist bowing a single string with their right (bow) hand and adding vibrato (pitch modulation) with their left hand. The bow puts the string in motion at a pitch of A440 (it carries the audio signal), while the left hand modulates the pitch by shortening and lengthening the vibrating string several times a second. The bowed string is the Carrier, the vibrato is the Modulator.

The frequency of the vibrato might be 4 cycles per second. Below our audible perception as a steady pitch… But you do hear the influence of this variation on the resulting sound. Dr. John Chowning, the Father of FM, discovered as you sped up the vibrato (modulator) you could effect a profound timbre change in the oscillator acting as the Carrier. Doing this electronically, he was able to speed the vibrato up to any frequency. As the Modulator frequency crossed into the audible frequency range, this caused a change in the overall tone of the resulting sound. And as the output level (called “modulator index”) increased so did the harmonic complexity of the results. Sidebands that included harmonic and even non-linear harmonic levels were generated and the complexity of timbre opened the door to a virtually unlimited range of tonalities.

Why this is musically important is sounds are made up of complex harmonic relationship, FM is a synthesis method that lends itself well to recreating both musical and non-musical timbres in an extremely wide variety of categories. Sound design with this FM engine can be mastered via this hands-on interface.

The Operator (oscillator) includes the sine wave generator, an Amplifier, an Amplitude Envelope Generator, and inputs from other Operators and the keyboard. This is different from the typical analog Oscillator – because it includes the EG as apart of this single block – each tone source has its own Amplitude Envelope. In your typical analog synth, the Oscillators share the same AEG.
The Amplitude Envelope Generator is responsible for changes in output level of this Operator over time. You can control how it comes in, what it does while it is in, and how it disappears when you let go of the key. In the analog world this was referred to as ADSR or Attack-Decay-Sustain-Release – four parameters that defined the “shape” of Loudness in the case of the AEG. On the reface DX, you have 8 parameters to define this shape. The parameters are four LEVELs and four RATEs.

Basically you control how fast (Rate) the envelope travels from one Level to the next. In future articles we will show you how to take command of these Rates and Levels to create the results you require. Rates have values between 0 and 127, where the higher the number the faster the travel… think of the rates as miles per hour… higher is faster. This is not a strict TIME parameter, because if the distance it has to travel is longer the same value for RATE may not result in the same amount of elapsed time. So Rates and Levels work in combination. A Rate of 100 does not denote a specific value of time, if the distance it needs to travel is greater, it simply will take longer to travel that distance. Think real world again: Even if you are moving at 100mph, if you have to travel a greater distance it does take more time.

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