What’s in a Vocoder – voice synthesisers and Robots

Kraftwerk, Styx and My Vocoder – Shaping human voices

Generating and shaping audio and RF wave patterns has long been an interest for many and is seen in the medical, military and commercial industries.

Not wanting to re-invent the wheel but rather looking at another spin, what is the appeal?

Although there are many makes and models, dedicated or otherwise two entry level but well rated models are the Roland VT-3 and the Paia Vocoder designed by Craig Anderton. Check out an upcoming series as we attempt to build our own.

An off-tuned SSB received signal through the BFO will create vocals which sound like monkey chatter or off pitch. It doesn’t take radio students long to see the multiple effects ring modulators and different tones have on the output.

Circuits and Kits

Instructables – Build and Analog Vocoder by Planetone

MFOS – Music from Outer Space / Article / Makezine

Ghetto Talk Box

Muffwiggler / Elektor 10 channel vocoder

And of course….

Crank That Soulja Boy Talk Box (from Ghetto Talk Box)

Audio Tools

Two of my favourite audio tools would be Audacity (free) -multitrack recording which allows effects and of course, Reaper, a fully equipped DAW.  Free for 60 days then although not crippled, $60.00. You will not find this kind of software anywhere for this price.

Both the above allows vocoder inserts and with proper manipulation are exceptionally good.


Further Reading

How Vocoders work – Craig Anderton (Paia)

The VCO or Voltage Controlled Oscillator

VCO in synthesisers

The VCO – the beginnings of a new era in synthesis

The voltage controlled oscillator is a very common circuit often used in conjunction with a phase locked loop circuit.  VCOs often use a varactor diode to control the output frequency of the oscillator. They are cheap to build and are often used in modular synthesiser designs.

VCO in synthesisers
Rick Wakeman – the king of Moog (photo credit above, Aurelio Moraes, live, Sao Paulo, Brazil)

This page is not necessarily a continuation of the building blocks in a synthesiser as the VCO in it’s own right makes for a very versatile piece of test equipment.

The VCO can have a control voltage which is fixed to get a single tone or the control voltage can be that from a modulation input which causes shift in pitch synched with the input control.

The VCO in a synthesiser is normally tuned to one of either:

  • Volts per Octave, the common standard used in Moog where e.g. in sequence each volt equals one octave. This is currently the more popular configuration;
  • Hertz per Volt, commonly found in Yamaha where each octave equals double or half one Volt.

The VCO is very versatile and in modular form will have a multitude of outputs, usually being ramp (sawtooth), triangular, sine and square. VCOs can be connected together through the control voltage, the outputs can be wave-shaped and of course, modulated from an external (or internal source).

One of my favourite circuits is brought to you by Analogue Designs, using the AD654

the VCO - analog designs AD654
Analogue Designs – AD654 – Technical Information


Some circuits of the VCO 

Schematic of popular but ingenious VCO by Thomas Henry on Birth of a Synth – Scott Stites.

Nuts and Volts, as always, gives a very interesting view of OTAs (Operational Transconductance Amplifiers – Part II the LM13700). Article by Ray Marston.

Onsemi MC74HC4046A – VCO/PLL

Further Reading:

Muff Wiggler – Wave Shape Transition (beyond the scope of a beginner but very interesting, thanks to “Highcooley”).

Experimentalists Anonymous – Oscillators, Minimoog VCO etc

Vintage Synthesisers using Ring Bridge Modulation

Oscillators for the Newbie – Positive Feedback

The 741 Operational Amplifier

FM in Music Synthesizers