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

Synth 76477 is a programmable sound effects generator, inspired by the famous SN76477 integrated circuit chip from the 1970s. It contains three adjustable frequency oscillators that can be slaved, as well as a noise generator and ADSR envelope.

Your virtual sound effects, called chips, are arranged as boards. Each board can have up to 50 chips (up to a 5 by 10 matrix). And you can create as many boards as you'd like.

When you first start the app, you'll see the list of boards, which initially contains just the default Sample board. You can create your own boards by tapping Edit then the green plus sign next to Add Board.

The sample board 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!

After you've read this help, exit it and tap on the Samples board to get started.

Tap on Setup to change the title of the board, or set the number of rows and columns. You can also export a board to a file, which you can copy off your device using iTunes File Sharing, or import a board from another device. This makes it easy to share your boards between devices.

Tap 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). Tapping 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, tap the Edit button, then tap 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 Color. There's a color wheel to select the color hue, and a slider for the brightness. The Copy and Paste buttons here let you easily copy a button's color, so you can use it elsewhere.

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 switch. When this switch 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 switch 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 switches 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 switch 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:

Tapping on Tools let's you do a few useful things:

You can copy a chip's settings, then paste them into another chip. This is handy if you want to use a chip as a basis for other chips.

You can also export and import chip settings. Tap export, and a file will be created with the same name as the board. You can use iTunes File Sharing to get the resulting file off your device, and copy it to another device.

To import a board, copy it to your device using iTunes File Sharing, then tap Import and select it.

To use iTunes File Sharing:

  • Connect your device to your computer, and start iTunes on your computer
  • Select your device in iTunes
  • Go to the Apps tab
  • Near the bottom of the iTunes window is File Sharing vUnder Apps, select Synth76477 on the left
  • On the right you will see all of the documents for this app. You can copy them off your device, or add new documents to your device.

You can also clear the chip settings with Clear entry.

Please feel free to contact us at with any suggestions you may have for the app!

Visit the Synth 76477 App page page for details on how to get the app.

Are you looking for a technology or radio related iPhone/iPad app but can't find one that does what you want? Have an idea for an app that you'd like to see? Contact us at!

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Last modified March 10, 2014