Session 03: Analog Oscillator Waveshapes

Objective: Hear and identify the four analog waveshape types -- sawtooth, triangle, saw-tri mix, and pulse -- and understand why waveshape is the foundation of timbre.

Warm-Up (2 min)

Load your basic patch (Bank 1, Program 128). Play a few notes across the keyboard. Solo Osc 1 (hold the OSC 1 button). Now solo Osc 2. They should sound identical -- both sawtooth waves, one in each stereo channel. Release the solo button.

Setup

From the basic patch:

• Set Osc 3 Level to 0 and Osc 4 Level to 0 (we only want to hear the analog oscillators)
• Keep Osc 1 and Osc 2 at Level 50

Exercises

Exercise 1: The Four Shapes (5 min)

Solo Osc 1 (hold the OSC 1 button). Hold down a note around middle C and change the Shape parameter through each option. Listen carefully to each for at least 5 seconds:

1. Set Shape to Saw -- you should hear a bright, buzzy tone. This is the "generic synthesizer" sound because sawtooth waves contain all harmonics. It responds very well to filtering (Anu Kirk p.11)
2. Set Shape to Tri -- you should hear a muted, flute-like tone. Triangle waves have very few harmonics, similar to a sine wave but with more character (Anu Kirk p.12)
3. Set Shape to Saw-Tri (the mix setting) -- you should hear something between the two: some brightness from the saw, but softer
4. Set Shape to P-50 -- you should hear a bright, hollow tone. This is a square wave (pulse at 50% duty cycle) which contains only odd harmonics (Anu Kirk p.12)

Now play each shape at a low note (C1) and a high note (C5). You should hear how the character of each shape changes dramatically across the range.

See Anu Kirk p.11-12 ("Sawtooth", "Triangle", "Mix", "Pulse Waves")

Exercise 2: Pulse Width Exploration (5 min)

Stay on Osc 1 solo. Set Shape to P-50 (square wave). Now slowly change the pulse width number:

1. P-50 -- full square wave, bright and hollow. You should hear the classic square wave tone
2. P-25 -- narrower pulse. You should hear a thinner, more nasal tone
3. P-75 -- wide pulse from the other side. You should hear it sound similar to P-25 (think about why -- the ratio is symmetric)
4. P-10 -- very narrow pulse. You should hear a thin, buzzy tone with less volume
5. P-01 -- almost nothing. The pulse is so narrow it barely produces sound -- "the pulse width will turn off at the two extremes" (DSI Manual p.15)
6. P-99 -- same disappearing effect from the other extreme

The pulse width determines the ratio of "on" to "off" in the wave. P-50 is equal (square). Moving away from 50 in either direction makes the sound thinner until it disappears at the extremes. This disappearing behavior is what makes pulse width modulation possible -- interesting territory for modulation.

See Anu Kirk p.12-13 ("Pulse Waves"), DSI Manual p.15 (Shape/PW parameter)

Exercise 3: Two Oscillators Together (8 min)

Release the Osc 1 solo. Now you hear both Osc 1 (left) and Osc 2 (right) in stereo.

1. Set both to Saw. Play a sustained note -- you should hear a full, classic synth sound in stereo
2. Set Osc 1 to Saw, Osc 2 to Tri -- you should hear the saw dominate but the triangle adds warmth and body underneath
3. Set both to P-50 -- you should hear a very hollow, organ-like quality

4. Set Osc 1 to P-48, Osc 2 to P-52 -- slightly different pulse widths. You should hear subtle movement because the tiny difference creates timbral interaction between the channels
5. Now set Osc 1 Fine to +3 cents, keeping both as slightly different pulses -- you should hear a slow beating/chorus effect from the detuning
6. Set Osc 2 Fine to -3 cents (so they detune in opposite directions) -- the beating should be richer now
7. Return both Fine values to 0 when done

See Anu Kirk p.11 ("Fine") for detuning technique

Exploration (optional, hyperfocus days)

• Try each waveshape with the 4-POLE switch engaged and LPF Frequency at 80 -- you should hear how filtering interacts differently with each shape's harmonic content
• Set both oscillators to Saw but put Osc 2 one octave lower (Frequency C-1) -- this is the classic sub-oscillator technique
• Find a waveshape combination you genuinely like and save it to an empty program slot

Output Checklist

• Can identify sawtooth, triangle, and pulse waves by ear
• Understand what pulse width does and why extremes go silent
• Heard the effect of detuning (Fine) between two oscillators
• Session logged in Obsidian daily note

Key Takeaways

• Waveshape determines the harmonic content of a sound -- saw has all harmonics (bright), triangle has few (muted), square has only odd harmonics (hollow)
• Pulse width controls the duty cycle ratio and the sound thins out toward the extremes, disappearing at P-01 and P-99
• Small detuning between oscillators (Fine +/- 2-3 cents) creates chorus-like richness without any effects

Next Session Preview

Next time you will use an LFO to automatically sweep the pulse width, creating the classic analog string sound. This is pulse width modulation (PWM) -- your first modulation technique, and it sounds great.