SumDif

Shakmat Modular 2HP
fw 1.1
UTILITY MIXER MULT

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Dual precision adder/differentiator. Each section produces A+B and A-B outputs from two inputs. Handles audio and V/Oct-grade CV with 0.1% resistors. Per-section -6dB jumpers.

Patch Ideas · 6

★ V/Oct transposer
Keyboard pitch into A · static offset CV into B · A+B delivers transposed pitch · A-B delivers inverse transposition for a stereo-mirrored voice
▸ Show diagram
Patch diagramPatch diagram with 5 modules and 4 connections. Modules: SUMDIF, Keyboard, Offset, VCO 1, VCO 2. Signals: 1 cv, 3 pitch.SUMDIFKeyboardOffsetVCO 1VCO 2A1v/octBcvA+B1v/octA-B1v/octPitch1v/octCVcvV/Oct1v/octV/Oct1v/oct121. transposed up2. mirrored downcvpitch
★ Mid/Side processor
Stereo L and R into A and B · Mid (A+B) into a reverb · Side (A-B) kept dry · second section (C,D) decodes processed Mid+dry Side back to L/R
▸ Show diagram
Patch diagramPatch diagram with 4 modules and 7 connections. Modules: SUMDIF, Source, Reverb, Output. Signals: 7 audio.SUMDIFSourceReverbOutputBoth -6 dB jumpers: ONAaudioBaudioCaudioDaudioA+BaudioA-BaudioC+DaudioC-DaudioLaudioRaudioInaudioOutaudioLaudioRaudio121. Mid2. Side dryaudio
Precision CV inverter pair
Two modulation sources into B and D · A and C left unpatched · A-B and C-D deliver inverted CVs for spreading modulation across opposite-polarity targets
▸ Show diagram
Patch diagramPatch diagram with 5 modules and 4 connections. Modules: SUMDIF, LFO 1, LFO 2, VCF 1, VCF 2. Signals: 4 cv.SUMDIFLFO 1LFO 2VCF 1VCF 2BcvDcvA-BcvC-DcvOutcvOutcvCutoffcvCutoffcv121. inverted LFO 12. inverted LFO 2cv
★ Buffered V/Oct mult
Single pitch CV into A · B unpatched · A+B and A-B both carry buffered copies of A with V/Oct accuracy preserved to cents
▸ Show diagram
Patch diagramPatch diagram with 4 modules and 3 connections. Modules: SUMDIF, Sequencer, VCO 1, VCO 2. Signals: 3 pitch.SUMDIFSequencerVCO 1VCO 2A1v/octA+B1v/octA-B1v/octPitch1v/octV/Oct1v/octV/Oct1v/octpitch
Sum & difference sidechain
Drum bus into A · bassline into B · A+B mix feeds main output · A-B (drums minus bass) feeds compressor sidechain for rhythmic ducking
▸ Show diagram
Patch diagramPatch diagram with 5 modules and 4 connections. Modules: SUMDIF, Drums, Bass, Mixer, Compressor. Signals: 4 audio.SUMDIFDrumsBassMixerCompressorAaudioBaudioA+BaudioA-BaudioOutaudioOutaudioInaudioSidechainaudio11. drum-only envelopeaudio
Dual CV offsetter
Two CVs through section 1 and section 2 · DC offset patched to B and D · A+B shifts CV up, A-B shifts CV down · four simultaneous offset variants from two modulations
▸ Show diagram
Patch diagramPatch diagram with 9 modules and 8 connections. Signals: 8 cv.SUMDIFLFO 1Offset 1LFO 2Offset 2VCO 1VCO 2VCF 1VCF 2AcvBcvCcvDcvA+BcvA-BcvC+DcvC-DcvOutcvCVcvOutcvCVcvFMcvFMcvCutoffcvCutoffcvcv

Behaviors

Unity Mixer two signals at A and B

A+B outputs the sum at unity gain. 3V at A plus 1V at B yields 4V at A+B. Suitable for CV summing (transposition) or audio mixing with 0.1% precision.

Signal Inverter signal at B only

With A unpatched and B carrying a signal, A-B outputs the inverted B. Turns SumDif into two independent inverters per section if A inputs are left open.

Buffered 1:2 Mult signal at A only, B unpatched

A+B and A-B both deliver a buffered copy of A. The precision buffers preserve V/Oct accuracy, unlike passive mults.

Mid/Side Encode/Decode stereo L and R at A and B (audio)

A+B = Mid (sum), A-B = Side (difference). Feed the second section C+D/C-D reversed to recover L/R. Both jumpers ON for -6 dB unity round-trip.

V/Oct Transposition pitch CV + transpose CV

Precision resistors keep V/Oct linearity within cents. Sum a keyboard CV with a static offset for exact-octave/fifth transposition or with an LFO for precise vibrato.

Controls

Section 1 -6dB Jumper (A+B) Rear jumper that attenuates the A+B output by 6 dB, preventing clipping when summing two hot signals.
ON = -6 dB (unity after two inputs summed) · OFF = full gain
Section 1 -6dB Jumper (A-B) Rear jumper attenuating the A-B output by 6 dB. Matches the A+B jumper so a Mid/Side encode stays unity.
ON = -6 dB · OFF = full gain

I/O

IN · 4

  • A CV or audio, V/Oct capable CV
    Section 1 input A. Summed with and subtracted from input B. Unused B input leaves A buffered through both outputs.
  • B CV or audio, V/Oct capable CV
    Section 1 input B. When A is patched alone, B is the inverted A (A+B=A, A-B=A).
  • C CV or audio, V/Oct capable CV
    Section 2 input C. Summed with and subtracted from input D.
  • D CV or audio, V/Oct capable CV
    Section 2 input D. Behaves identically to B for the second section.

OUT · 4

  • A+B sum of inputs CV
    Section 1 sum. Unity mixer of A and B (or -6 dB with rear jumper). Precision enough for V/Oct transposition.
  • A-B difference of inputs
    Section 1 difference. Subtracts B from A. With B unpatched, acts as a buffered mult of A; with A unpatched, outputs inverted B.
  • C+D sum of inputs
    Section 2 sum. Identical behavior to A+B.
  • C-D difference of inputs
    Section 2 difference. Identical behavior to A-B.