MATRIXSYNTH: Roland GR-300 Waveform Mod


Tuesday, March 22, 2016

Roland GR-300 Waveform Mod


Published on Mar 22, 2016 Expedition Electronics

"Excuse the tuning issues; I should have tuned the guitar and the synth to the guitar

Roland GR-300 mod to provide variable pulse width waveform, PWM, and filter mod from a tap tempo LFO. I did a poor job describing how it works. Essentially, as part of the pitch determination the GR300 samples the height of a ramp wave (the same wave used as second oscillator in Duet mode) on the zero crossing of the incoming signal. That means the sampled voltage gets larger the lower the frequency of the incoming signal. This sampled voltage is used as the reset point for the main ramp oscillator. Therefore, that voltage is equal to the peak voltage of the oscillator sawtooths (ramps, really). So, the servos figures out how much to attenuate that sampled, relatively stable, voltage to bring it to a constant level and applies the same attenuation to the oscillator waves. Thereby, making the output of the oscillators have a fixed height as they would in a normal synthesizer. From there, standard synth stuff to do PWM."

Update:

Multiple Filter Modes for Roland GR-300

Expedition Electronics
Published on Aug 10, 2017

"Second in the series of Gr-300 mods and it's a long one! This mod provides 15 different filter modes in a similar manner as the Oberheim Xpander. I ramble on through the list of modes first without playing the synth. Actual synth output audio starts at about 5:30. Skip ahead if you want to get right to it! The synth output is panned mostly left and commentary mostly right if you want to try to balance it (or want to mute commentary)

Just near the end I mention a 3 bit DAC, but I should have said 3 bit ADC."

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