Synth 76477 - A sound effects generator and synthesizer app for your Macintosh!

Synth 76477 is a powerful sound effects generator and synthesizer app, inspired by the famous SN76477 integrated circuit from the 1970s, but containing many enhancements.

Features:

Three oscillators, each of which can produce a sine, triangle, sawtooth, or square wave
The outputs of two of the oscillators can be used to modulate the main oscillator
Frequency modulation can be linear or octave based
The duty cycle of the main oscillator can be adjusted in square wave mode
Noise generator, either analog or digital, with an adjustable low pass filter
Oscillator outputs can be mixed to the audio output
Fully configurable ADSR (Attack / Decay / Sustain / Release) envelope, linear or exponential
One shot mode available
Unlimited number of sound effect generator boards
User configurable array of sound effect generator buttons on each board

Synth 76477 comes with a full set of sample sound generators, making it easy to understand how to use and configure them, and tap the full power of the app.

The sample board (you can open it from the File menu) has a bunch of examples to show off the capabilities of the app, and help you understand how the various settings affect the sounds that are produced. But the best way to learn is to just play around!

Click on one of the chip buttons to start generating that sound effect. Some sounds continuously play, others only play while the button is being pressed, they have the electronic symbol for a momentary switch in the background (you can control this behavior). Clicking the chip again will stop playback. Note that some effects use the ADSR envelope, so the sound will fade out, and not instantly stop.

To edit a chip, right click on the chip. When you do this, you'll be shown all the settings for the chip, and it will start to play unless One Shot mode is set, then you'll need to touch the One Shot button for it to play. There's a lot of settings, so let's go through them:

First, you can edit the name of the chip, which is displayed on the board. You can also change the button color by tapping on the colored box next to Color. A color wheel will appear, to select the color hue, and a slider for the brightness.

Each chip as three audio generators: The VCO (voltage controlled oscillator), LFO (low frequency oscillator) and SLF (super low frequency oscillator). The names are mostly historical, they all cover fairly wide frequency ranges.

First are the controls for the VCO. There are a set of buttons to select the waveform type: sine, triangle, sawtooth, or square. Then the volume and pitch (or duty cycle) can be set. Finally there is a slider to set the center frequency.

The LFO and SLF oscillators are similar, but with a few differences. There are no volume and pitch controls, but there is a set of buttons to select the frequency range.

There's also a gain slider for each, with an associated toggle button. When this button is turned on, the output of that oscillator can be used to vary the frequency of the VCO. That is, it frequency modulates it. The gain controls how much the VCO frequency varies, and and can be negative, so that for example the sawtooth ramp becomes inverted.

Here's how modulation works. There are two audio waveforms shown below. The top one is the VCO signal, the bottom one is the modulating signal (either the LFO or SLF). You can see how the VCO frequency varies, depending on the amplitude of the modulating signal:

In this example, the modulating waveform is a sawtooth

And here is another example, but this time the modulating signal is a square wave, rather than a sine wave:

By default the relationship between the LFO or SLF signal and the effect on the VCO frequency is linear, but if the Octave toggle button is turned on, then it becomes octave based, which often sounds more natural.

A noise generator is also available. It can produce either analog or digital noise, the pair of buttons with a sine and square wave respectively set this. There's a slider to adjust the amount of low pass filtering applied to the noise signal.

Four toggle buttons control which of the oscillator outputs (VCO, LFO, SLF, and noise) are applied to the output sound. The mixing is done in a multiplication fashion, rather than addition, so think of the mixer as being a giant AND gate, rather than an OR gate.

Finally there is the ADSR envelope control, which affects the amplitude of the signal. There are eight possible settings:

Mixer - the audio has no envelope applied to it
One Shot - the envelope starts when the One Shot button is pressed, and is sustained as long as it is pressed, then moves into release mode.
VCO - the envelope starts and stops with the VCO signal
Alt VCO - the envelope starts and stops with every other VCO signal, with a dead time between
LFO - the envelope starts and stops with the LFO signal
Alt LFO - the envelope starts and stops with every other LFO signal, with a dead time between
SLF - the envelope starts and stops with the SLF signal
Alt SLF - the envelope starts and stops with every other SLF signal, with a dead time between

The envelope is a standard ADSR envelope:

Attack - the initial rise of the signal, when it is triggered
Decay - the falling of the signal down to the sustain level
Sustain - a constant amplitude applied to the signal
Release - the falling of the signal down to zero after the sustain period ends

When the exponential toggle button is on, the applied envelope is smoothed as with an analog RC circuit. Otherwise, it is linear. The four ADSR periods are drawn so you can see their effects. Note that the absolute time of the sustain period is not actually used in the display, since it can vary due to how long the One Shot button is pressed, or the actual period of the triggering oscillator:

Email your comments and questions to info@blackcatsystems.com

Last modified December 7, 2014