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 MicroKorg and other Best Selling Synth

Korg M1 - By Deepsonic, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=66234414

Best selling synthesisers of all time

Just in case you may have the MicroKorg don’t be too surprised to know that it may just be one of the best selling synthesisers of all time.  Without having the data from any manufacturer readers may not be entirely convinced but considering that they have been manufactured since 2002 reflects the popularity of this model series.

The pure versatility that digital or DSP driven synths brought to the market ensured a very quick surge in sales especially in the home and garage band amateur and pro space. Having purchased a CZ1000 in the mid 80s whilst in Yokohama it became more a showpiece until a musician friend showed me the full potential. Sadly it was stolen about two years later, possibly as a result of its popularity. 😈  Continue reading “The MicroKorg and other Best Selling Synth”

Applying Digital Electronics to Stomp Boxes

Simplifying matters with the Arduino Due – Digital Stomp Boxes

Stomp boxes have been with us for ages, giving Hendrix, Slash, Gilmour and Page their famous signatures.  Of course the older stomp boxes were tube and semiconductor devices, the diodes and transistors used being more often the Germanium type and even today the Ge semiconductor is a sought after  commodity for it’s own unique blend of sound.  Continue reading “Applying Digital Electronics to Stomp Boxes”

Total Harmonic Distortion meter

Hantek DSO

THD Meters – how they work

Many years back the must haves for anyone building audio equipment would have been the multimeter (DVM), oscilloscope and a function generator. With specialised audio test equipment falling in price over the last twenty years two other pieces of equipment are now also found on the test bench, the THD meter and spectrum analyser.  Indeed your laptop or desktop could be used for many of these functions but it can be cumbersome and/or inaccurate because of sound-card bandwidth limitations.

Hantek DSO
Hantek DSO – 1202B

The THD Meter is definitely a must have, even something for impressing one’s audiophile friends.  Consisting of an oscillator, internal or external, a notch filter to attenuate the fundamental to as little as possible and a voltage / instrumentation amplifier to drive the resultant combination of harmonics and noise to the output meter or video graphics display.

Block Diagram of THD Meter using Wien Bridge Notch Filter
Block Diagram of THD Meter using Wien Bridge Notch Filter

Interesting DIY angle to THD metering from “Wensan” – DIY Audio – Simple THD Meter

Robert Cordell,  American (as in USA) electrical engineer and expert in the audio field kindly publishes his high end THD Analyzer circuit on his website, Cordell Audio.

Analysing the Waveform – skirting the FFT

The analysis of signal waveforms is rather mystical to most of us and becomes a highly complicated mathematical subject when breaking a signal or rather batch of frequencies down to a function of time. FT, or Fourier Transform converts the waveform data in the time domain into the frequency domain each containing individual signals of phase, amplitude (magnitude) and frequency.

Modern computer software makes this previously time consuming and highly mathematical task accessible to the home experimenter using what is now commonly known as FFT or Fast Fourier Transform.

Digital Signal Processing

Digital signal processing in the modern computer has made decomposition of signals in audio a common discussion point on the forums, possibly not always in our best interests because of the complexity and hence confusion.

FFT and Nyquist are of interest to the engineer, especially now in the DSP domain where bit rates and sampling frequencies have become an integral part of our lives.

Our modern (and even older) hardware can run software for analysing and changing the audio signal – and sometimes it’s free. See Audacity and it’s features.

Shit in Shit Out

Technically speaking it is not probable that an ill designed amplifier using inferior components will sound good. 🙂

It is probable that with the assistance of application notes, spec sheets and white papers from most manufacturers to build a quality product with the minimum of fuss.

Hantek  – USB oscilloscope, multi-function

I have four oscilloscopes, three of them analogue. I like the ease of triggering and set up. Coming from the analogue era certainly assists – the digital scopes don’t appeal from a GUI perspective until one needs to record an event or compare functionality to price. They become indispensible. Just look at the hand-helds.

The digital scope I use is the Hantek 3062. It has a logic and spectrum analyser, frequency counter and of course it’s a scope.  It cost about R4K five years back from Kmeasure, based in Pretoria. Very good service. I mention this as an aside, there are always sensible, cost effective solutions in our pinched South African market.

Lastly, of course we need a good quality function generator.  I find Instek to be of exceptional quality and reliability. Available at Mantech Electronics. (Cape Town, Johannesburg, Durban).

Further Reading:

Cordell Audio:  Robert Cordell Build your own THD Meter

KMeasure – Professional measurement systems (based in Pretoria)

Signal Lab – SigView Signal Analysis software

The VCF or Voltage Controlled Filter



The Wien Bridge Oscillator

The Merits of Wien Bridge Oscillator types

The Wien Bridge oscillator is an oscillator type used in many circuits which rely on a sine wave to drive or act in part on a circuit designed for another purpose.

The Wien Bridge oscillator is possibly one of the more versatile and easier to build circuits, used often to generate a 20Hz to 20kHz sine wave for testing audio equipment.

The Wheatstone Bridge

But first of all, let’s look at the Wheatstone Bridge, another very important circuit and used to accurately measure very low (or high) resistances.  Most Ohm Meters or resistance checkers are not accurate when going down to below a few Ohms and the Wheatstone Bridge is the solution.

Wheatstone Bridge
Wheatstone Bridge

The circuit above works on the theory that if the potential difference across a Volt meter (galvonometer, a device which measures electric current), there would be no deflection of the needle as no current flows through the meter.

Now if there are two known resistors in circuit plus a carefully calibrated potentiometer, VR1 we can use the above circuit to calculate an unknown resistance.  If this was a device used to measure very low resistances, in the order of 0.1 Ohms we would have a current limiting resistor in the circuit, possibly in the (+) line of the PSU.

E.g R1 = 4.7 Ohms, R2 = 2.2 Ohms and the meter shows no deflection when VR1 is set to 4 Ohms the formula above would give an output, read off the potentiometer indicator as 1,87 Ohms.   Read up on Kirchoff’s Law.

This circuit is used for impedance measurement as well. Below is another variation, the Wien Bridge:

Wien Bridge (for capacitor check)
Wien Bridge (for capacitor check).

The Wien Bridge, known after Max Wien is similar to the Wheatstone Bridge where the potential divider networks need to have an equal ratio to null the network. This is often used to determine, capacitive, inductive (Maxwell-Wien), frequency and resistive values. In an AC circuit things become more complicated and a damned sight more interesting than DC. Both capacitive (Farad) and inductive (Henry) values need a known frequency to determine the capacitive or inductive reactance, resp. Xc or Xl. Xc = 1/(2πfC) and Xl = 2πfL.

In the circuit above there are two variable components, the capacitor C1 and VR1 in parallel. The component being checked is a capacitor which also has a high internal resistance.  By adjusting VR1 and C1 a null will be reached where the values of the two variable controls are read off and the parallel impedance calculated, and likewise the values of unknown components calculated through the null value balanced equation Z1/Z2 = Z3/Z4.

The Wien Bridge Oscillator

Basic Wien Bridge Oscillator
Basic Wien Bridge Oscillator – note the series R1C1 and parallel RC networks R2C2

The Wien Bridge oscillator is based on the bridge circuit.  The circuit above is the classic student’s build using a small incandescent bulb in the circuit to control the amplitude. (AGC).

The capacitors and resistors are of the same value. The result of this is C1 = C2 = circuit C and R1 = R2 = circuit R.  Frequency of oscillation is calculated as being 1/(2 * π * R * C).  Rf  is the positive feedback resistor.

A stable oscillation output is determined when the bulb filament resistance is equal to the feedback resistance / 2 or Br = Rf/2

Sine wave output is generally of good quality, undistorted and even amplitude. Limitation is generally only the lower frequency range, making it good for testing audio equipment.

Next:  Total Harmonic Distortion meter for audio equipment





Roland CR 800 and BOSS – the legend continues

boss ds-1 simple block

The Rhythm Composers

Although I am not big on rhythm composers and generators the articles covering electronic music synthesis would be totally irrelevant without at least a few lines on the TR-808 and a few other “drum machines” which come from the analogue era of the 60s to 80s and dare I say, even today.

Ikutaro Kakehash founded Roland after huge success with his pioneering company, ACE Electronics. Some of his better machines using the then cutting edge technology were passed on to Roland, one machine being the TR-77 Rhythm 77.

The early 70s brought on the TR series (Transistor Rhythm) and then later, the CR where the CR-78 became the first machine which utilised integrated circuits (this I believe was the first of it’s kind).  The CR-78 was cloned recently by the French company Cyclone Analogic, named the TT-78. Although the CR-68 was limited in functionality unlike the 78 with programmable memory it was popular at the time due to it’s lower costing. The CR-800 is another classic, more known for it’s rarity however. The unit came complete with amplifier and floor mounting loudspeaker.  Great bit of kit described here with images.  Personally, I have never seen one of these units in South Africa.

The Dr-55 became a model which was most famed for stepped rhythm programmability. It was simple, it was cheap and as students we all tried to emulate the circuits as electronic students.

Big Brother TR-808

This conundrum (pun intentional) of an electronic drum generator was supposedly one of Roland’s biggest flops, an all analogue synthesiser which was designed to compete with the digital sampling Linn LM1. Although the TR-808 was marketed at nearly quarter the price of the LM1 and was initially scoffed at, it was used on more labels than any other machine in history.  One needs to remember of course that our most talented musicians and sound engineers are a pool of creativity and the only limitation to any synthesiser is really only the user. Being a highly affordable and analogue drum machine lent itself perfectly to “bending the rules”.

Although Roland continued to bring out analogue machines until the mid-80s, drum synth became hugely popular on the hybrid and digital platforms, memory storage and programmability being a huge plus.

BOSS Pedals

BOSS is a division of Roland and amongst the many achievements it can boast of, is also the proud manufacturer of some of the world’s best and unique stomp boxes,  guitar pedals and synthesisers.

Although the advances in digital technology has reduced pricing of all-in-one packages it’s certainly no surprise that most guitarists, hobbyists and professionals alike, veer towards their favourite.  And this, more often than not would be the analogue pedal, the one that screams and shouts, gives blisters and tears skin off the otic canal.  Flangers, distortion, phasers,  echo, delay, chorus,  screamers, overdrive, fuzz, modulators, tremelo, you name it, they have it.

My favourite Two (out of Ten)

OK, let’s be realistic.  Certain styles of music lends itself to guitar synth but not all. Here we single out the player and his or her style. I don’t know what a Stratocaster will sound like played clean but maybe I don’t want to. Hendrix was a great user of Wah and Fuzz.  In my mind he could have used any effects pedal and one would know it was Hendrix.  A very under-rated guitarist is Mark Knopfler.  I think he was positioned at number 25 in Rolling Stone mag a few years back.  He may just be genius – I give him full credit.  Orange Whip Compressor, Cry Baby, Volume make up his distinct sound. I don’t think any pedal will bring out his distinct sound – he was (is) never a show off.

Guitar pedals are not full of magic. In our previous articles on music synths we touched base on some of the tricks used.  All the effects used by all the musicians in one box is the big advantage of digital.  Multi-FX, used in the BOSS ME-80. At a touch over R5 000.00 this is not a bad buy. Of course there’s literally hundreds of multi-fx pedals being sold these days so one can take their pick.

boss ds-1 simple block
BOSS DS-1 – simple block

This subject to be continued – a base for effects in guitar, circuit description and how it works.


Further reading:

From FACT magazine

In 2004, John Wood stood outside Hollywood’s Amoeba Records, selling bumper stickers emblazoned with the slogan: “Drum machines have no soul”.


Electronic Kits and Synths

eti4600 - voltage controlled synth

Electronics:  Kits and Synths

Minimoog VCF

A word of thanks to Paul in Cape Town for this great link:  Minimoog VCF – interesting that one can bounce around the internet and miss some gems.

The patent 3475623

Voltage controlled filters, although covered only on a surface level is daunting at design level but is an area in which Robert Moog excelled. Of course we couldn’t write this paragraph without including Moog’s patent 3475623 – 3974461 (David Luce: Inventor)

Patent 3475623 is a very important part of electronic music, then and now – covering VCFs and termed or rather more commonly known as the Ladder Filter. An excellent article can be  found on the Sage Audio website,  The Importance of Patent 3475623 (A Celebration of Robert Moog’s Influence on Modern Recording).

Sound on Sound:  The ladder filter

Moving on to our own home front I am pleased to see that Yebo Electronics in Cape Town is now selling a Class D amplifier 20Hz ~ 20kHz  100W+100W. Sold as KIT63S for about R600.00.

class d 100wx 2 south africa
Class D Amplifier 100W x 2 at 32V DC – TDA7498  Min load 6 ~ 8 Ohms

Fatman Kit – PAIA

A remarkable synthesiser which is also affordable.

fatman 9308 analog midi
                                    Fatman 9308 Analog Midi

PAIA is world renowned for some amazing kits:  The above, Fatman Kit retails for about 200$. 9308K US version, KP international 220V, 9308FP, rack mount chassis about 35$ and 9308C, Case, 53$. Also Vocoders and tube preamplifiers.   The more expensive synthesiser kits, the 9700, sell for about 600$. Description: P9700S Series Analog Synthesizer Modules

The Maplin ETI4600 Synthesiser

Now here’s an interesting one.

Trevor Marshall

An Australian design, was it a rival to the American Moog products? The 4600  was designed by Barry Wilkinson and Trevor Marshall (Australian electronics engineer and scientist) for “Electronics Today International” in the  70s.  An important criteria for Trevor Marshall was to make his work accessible to those that could not afford the high end synths of the day and sadly, in so doing he didn’t make any financial gain out of the project.  His genius and passion will always be remembered by ETI readers of the time. (and not unfortunately his dealings in the medical profession, he was after all an electrical engineering graduate).

Complete construction details can be found on the ETI4600synthesiser.org website.  Although an exciting build for any awe struck electronics enthusiast it also came at quite a price. I do believe in South Africa, at the time, the pricing was set to about R10 000.00 for the 4600.

There are numerous articles on the 3800~5600, one being at Future Software.

With all the technological advances in electronic music, effects, computers and VST there is still a staggering amount of musicians, DIYers and professional audio manufacturers sticking to the rules of analogue.  Of course here we should always credit the pioneers, Moog and Marshall for their incredible work.

The ETI 4600 – Voltage controlled synth

eti4600 - voltage controlled synth
                                                                 Voltage Controlled Filter – ETI4600

SA Music – The beginning of the beginning

South African Music – our musicians, not really but nearly!

Manfred Mann, rather then Manfred Sepse Lubowitz, was born in South Africa in 1940.  I would hasten to add that we all like to see him as a South African,  like Elon Musc, but truth be told much is driven by influences within the musician’s host country.

Famous as a musician first and foremost, then for the hits “Do Wah Diddy Diddy”, “Pretty Flamingo” and “Mighty Quinn”, then Manfred Mann and now Manfred Mann’s Earth Band was and still is an inspiration to many song-writers.

I have added Manfred Mann to our “SA Music” articles page because he is after all native South African, he did leave South Africa most probably due to political pressures at the time and the article that most gave insight into the Mann we know comes from an interview with Andrew Brel of Keyboard Magazine in 1993.

Oh yes, nearly forgot – Manfred Mann is known for his solo acts on the Minimoog synthesiser. Let that not be forgotten. Please read up on the series based on synth modules used in analogue synthesisers.

And of course, this could not be complete without the famous Bob Dylan track, “Quinn the Eskimo (Mighty Quinn)”

And next, moving on to our top export, “Mchunu’s Bull”. (Coming Up)

Ring Bridge in Audio Synthesisers

Kraftwerk - the minimoog

Ring-Bridge Modulation for Audio

The audio synthesiser uses two popular means of modulation, one being the popular VCA or voltage controlled amplifier, also commonly known as a 2-quadrant multiplier and the other, the 4-quadrant multiplier.  The 2-quadrant multiplier accepts a unipolar signal, the 4-quadrant, a bipolar signal.

unipolar vs bipolar wave
Unipolar Vs Bipolar Wave – the unipolar only covers the positive region, bipolar swings to negative.

The VCA uses a control voltage (CV) to modulate the amplitude of the signal, this can be anywhere between 0V to max carrier amplitude or Vcc. Bear in mind that the carrier need not be a continuous sine wave of fixed amplitude but also a signal of differing amplitudes and wave shapes.



Kraftwerk - the minimoog
Kraftwerk –  Andriy V. MakukhaOwn work. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Above:  Kraftwerk co-founder Ralf Hutter used a Minimoog in their highly successful album, Autobahn.

The ring modulator (RM) is also known as the Ring Mixer although purists prefer the term Ring Modulator or 4 quadrant multiplier.

We briefly covered the ring bridge modulators used in SSB and you will notice that the audio and RF modulators amount to the same thing (albeit minus the sometimes tuned LC circuits). The Hugh Davies modulator uses a 1:1 transformer.

The above video is a very good demonstration by an accomplished user in the power of the Minimoog.

Playing around with the side-bands generated in a modulator creates the unique sounds of an analogue RM/synth. As many have discovered, the analogue synthesiser is very much still in demand as can be seen on eBay, with prohibitive pricing. Digital processing has become more the de facto but in tonal quality (and this I really do mean unique to analogue) the analogue VCAs, VCOs and filters have kept the analogue synth very much alive. Price wise, digital is king.

Beginning topic:  The Ring-Bridge Modulator

Next: Where does it all fit in and Minimoog breakdown

Further reading:

The AD633 – Analogue Systems Low Cost Multiplier

Hugh Davies Ring Modulator

Analogue Ring Modulator Guitar Pedal – Daniel Klingler and Prof.  Steve Errede


Passive Ring-Modulator Kit

Yusynth Kit – dual RM

MFOS RM – Soundtronics (UK)


Miniwarp 633 – Marc Bareille

And to end off 🙂