Ambisonic Pan-Rotate

Posted on Feb 18, 2013

LM13700 VCAs are used in a configuration identical to that shown in the Nat Semi data sheet that produces minimal distortion. It is not perfect but then VCAs never are. Two VCAs are used in inverse polarity for each of the X and Y multiplier sections to guarantee zero output for zero control current. This ensures that change of control voltage amplitude will only result in increased gain and not an imbalance in the B format signal. (This could happen if one VCA was used as a four quadrant multiplier) The reversible quadrature oscillator from the frequency shifter project is used to provide the sine-cosine control voltages for automatic rotation of the output signal. An X-Y joystick with circular outer restraint is used to provide manual sine-cosine voltages for manual signal rotation.

Ambisonic Pan-Rotate
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Controls and Inputs: Mono to B-format Section Mono source input 1/4 inch jack unbalanced mono B format output 5-pin XLR unbalanced LOG CV input 1/4 inch jack mono LOG manual control ordinary pot LIN CV input 1/4 inch jack mono LIN manual control ordinary pot Oscillator LOG/LIN switch toggle Oscillator range switch toggle Oscillator direction switch toggle Joystick - oscillator select Pan-rotate control joystick Pan-rotate CV input, 1/4 inch jack stereo, shield GND, X control ring, Y control tip, +/- 1V The rotate mode switch is set to oscillator. The ACW-CW switch is set in either position depending on the clockwise/anti-clockwise sense of rotation required. In this mode the sound is continually panned around the soundstage at a frequency set by the oscillator. For conventional operation the oscillator will be set to the LOW position for slow rotation. In the HIGH position the sound will be spun around at audio frequency so that unusual rotation-modulation effects can be created. The oscillator has two modes of control those being LOG or LIN. In the LOG mode the direction is set solely by the ACW-CW switch and the speed is set in a logarithmic sense by the manual LOG control. Alternatively the oscillator can be controlled in this mode by an input voltage which obeys the 1V/octave synth control law. The voltage is fed into the LOG CV input which overrides the manual setting control. This gives the...

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