Richard Atkinson

Web Audio MOS 6581 SID simulation

This is a Web Audio simulation of my software for the HardSID card. Every button or slider on this interface (except the Start / Stop button) corresponds to a button or knob on the Behringer BCR2000 MIDI control surface which is used to control the SID sounds. In the HardSID version, the pitch and duration of the note can be controlled using a MIDI keyboard or sequencer.

Some differences exist between the capabilities of the Web Audio software synthesizer and the MOS 6581 digital/analogue hardware synthesizer. Rather than emulate SID exactly, this simulation allows some Web Audio characteristics to be explored, and also reveals differences between browser implementations (Chrome and Firefox).

Filter cutoff may be varied between 20 Hz - 20 kHz. Resonance may be varied up to 1000, which is an enormous value for any hardware resonant filter. This will distort the output of the Web Audio simulation, so to reduce the final output gain a Volume slider is provided (equivalent to register $18 in the SID). Filter modes are low pass, band pass, high pass, notch and all pass in the Web Audio simulation and the oscillator waveforms available are sine, triangle, sawtooth, square and pulse.

Global controls

Cutoff
Resonance
Filter mode
Volume

Oscillator one

Coarse tune
Fine tune
Waveform
Pulse width
Attack
Decay
Sustain
Release

Oscillator two

Coarse tune
Fine tune
Waveform
Pulse width
Attack
Decay
Sustain
Release

Oscillator three

Coarse tune
Fine tune
Waveform
Pulse width
Attack
Decay
Sustain
Release