Gate Man II

Author: Scott Gravenhorst

GateMan II & III

GateMan II

  • - (GateMan II, version g - Last updated 09-23-2007), includes GUI patch editor (VB.NET 2005) and sample patches.

The features are essentially the same as for GateMan I. There were minor changes to some modulation sources. The main improvement was replacing the audio path single stage IIR filter with a digital state variable filter. The filter makes a big difference in the synth's sound.

The new patch editor adds a slider for filter Q (1.0 to 23.4) and what I call a DAC window. I found that the amplification with higher Q settings could cause distortion which I first fixed by manually changing the window position in Verilog, so it seemed sensible to make this a user control. The DAC window value defaults to zero, which can cause zero output. Most of the patches I've made have a setting of 15 or 16. The setting changes the position of the 12 bit window into the NCA output used to present data to the DAC.

New Features

  • Oscillator Synch (09-22-2007)

Sample Sound Files

Here is a sound file, just some notes, the patch is something I call "grinder5", included in the (above) zip file. Velocity is controlling the filter corner frequency in the sustain stage of the NCF ADSR, filter Q is set to 10.0. Two oscillators are set to saw, two are set to velocity controlled PWM. All oscillators have a varying amount of pitch modulation by filtered noise.

Both NCO pairs are synched, all sawtooth, but set slightly differently. (the clicks were caused by a problem found in the NCF ADSR and has been fixed in version f)

GateMan III

GateMan III is a yet unreleased version of this monosynth. GateMan I and II are both very "flat" flipflop heavy designs. GateMan III replacess addressable flipflops with distributed RAMs to reduce routing and total slice usage. The design appears to work at the moment, but is not tested thoroughly enough to release. The slice count was reduced about 5 percentage points and is currently just below 50%.

Once I determine that all functions are working correctly, I want to add some things:

  • LFOs to modulate pitch
  • LFOs will be added to the ADSRs to modulate during sustain
  • Ring modulators which will be assigned similarly to the GateMan II hard synch
  • Noise source included as an additional NCO waveform

Due to the changes required to convert addressable flipflops to RAMs, the synths internal address map had to be changed. Because of that, the GUI patch editor will be replaced with a new one which will work only with GateMan III. Older versions will not work correctly. Because the order of the patch data words was preserved, GateMan II patch files should still work. Even GateMan I patches will work, but may need tweaking and resaving because GateMan I does not have the DAC window parameter and the GateMan I patch editor doesn't save data to it's file location.