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Custom modular synthesizer

alien music

<![CDATA[]]>@charlesjuliank<![CDATA[]]> <![CDATA[]]>rabidaudio/synthesizer<![CDATA[]]>

???

I'm Julian. By day I write software for drones, and by night I make side projects. As the week progresses my nights take over my days, so I freelance hardware and software development so that I can just do side projects for a living.

Today I thought I'd show you one of my side projects, the synthesizer I'm putting together, and maybe inspire you to dive into hardware.

I figure most of the people in this room are software people. And I suspect there are a few people who've maybe played with an arduino or a raspberry pi, sensors and LEDs and the like, but the thought of transistors or capacitors intimidates you.

Well, synthesizers are a great jumping off point into analog electronics.

Why synthesizers?

???

So why learn electronics with synthesizers?

1

human

???

It's a form of artistic expression. connecting the technical with the artistic.

It's very sensory driven. Turning knobs changes what you hear, etc.

2

old

???

This stuff is old-fashioned. Nowadays everything is smaller, more complicated, and harder to use. Old stuff like this, the components are bigger, the circuits are simpler, and the patents have started to expire.

3

$$$

???

Original modular synths which used to be trashed for parts are now selling for thousands or tens of thousands of dollars. Analog systems are starting to make a comeback, and I think it is thanks to an intersection between the DIY maker community and the rising popularity of EDM and Dubstep.

Anatomy of a synthesizer

pitch

loudness

timbre

]

frequency

amplitude

shape (harmonics)

]

???

Some of you probably don't have any idea how a synthesizer works or what it does, so here's a very brief, simplified introduction.

When making music, you've basically got control of three parameters:

pitch
loudness
timbre

These are directly related concepts to signals:

frequency
amplitude
shape (harmonics)

???

Demo 1

I have here a Moog Werkstatt. It's an open-source hackable synthesizer.

First we use an oscillator to make a wave. We can control the frequency, and the shape (square vs. saw). Then we pass it through a filter, were we can control more of the shape by cutting off higher harmonics or even adding more. Finally we pass it through an amplifier to control the loudness.

Filter cutoff is wah sound for guitarists in the room

So the nice thing is all of these are modules

Modularity

Where the magic comes from

???

All modules basically work like so.

You have a signal input and output, and you control how the signal is changed through control voltages.

???

So here's the same diagram for the filter i just showed you.

VCF stands for voltage controlled filter

We've got two controls for our filter, cutoff frequency and resonance. it would take too long to explain exactly what the resonance does, but for now just know it adds higher harmonics.

Modulation

???

And Modularity gives us Modulation

GO BACK TO DEMO

filter sweep at a regular rate? External modulation: LFO filter sweep Vibrato FM modulation

So what did you build?

LFO

Oscillates roughly .1Hz to 100Hz
Square and triangle outputs
Adjustable amount

???

Go back to demo

just my LFO
my LFO at a different rate than bult-in
mine adjusting the rate of the built-in

Sequencer

Record patterns and play them back
Change the playback rate
~30 seconds of record time
reverse mode
trigger mode

???

Demo!!!

show recording a pattern
changing speed
reverse mode
trigger mode

You might notice it's a little out of tune. the ATMega has 10 bit DACs and ADCs, so a single bit of variation is a pretty significant pitch change (you can hear it)

I bought some external 16-bit DACs and ADCs. However, they are really small

Memory

onRecord

onPlay

]

short buffer[512];

while(record){ buffer.push(analogRead(input)); }

while(play){ analogWrite(buffer.next(), output); }

]

???

Here's the basicly what the microprocessor does it half-C, half-javascript Frankenstein pseudo-code.

The source code is out on the github link if you want to see it.

TI ADS1110

16-bit I2C

adc

???

Doing PCB layouts in Eagle. The Schematic is done

???

The board needs a little work

Others

Octopus VCF

???

For class, we build a Low pass filter using Vactrols, which are LEDs glued to voltage-controlled resistors.

We 3d printed a little box for the LEDs and designed the board.

Had to turn it in, so I couldn't bring it but to show, but I'm going to make another one soon.

???

4-pole lowpass filter
cutoff and resonance controls
custom vactrols
combined Buchla's vactrol current circuits with Ray Wilson's 4-pole design

Second VCO

???

I'm also adding a second VCO to the mix.

It doesn't work yet, and you can probably tell why.

It will be tunable relative to the first vVCO so they can be in tune, or in thirds, or fifths or octaves above or below

Future work

Entirely custom modules
3 filters: 4-pole LP, HP, state-variable
Buffed-up VCA
Extra LFOs
Second VCO with relative tune
MIDI keyboard
Patch memory

???

replace Werkstatt with all custom modules
3 filters: 4-pole LP, HP, state-variable
buffed-up VCA
- individually-controllable inputs (mixer)
- higher output
- stereo output
- ability to invert stereo phase
a couple 4-decade LFO's with clock input, PWM control
second oscillator with relative tune control
MIDI keyboard+EV replacement
patch memory

Learn more

<![CDATA[]]>rabidaudio/synthesizer<![CDATA[]]> <![CDATA[]]>rabid.audio/blog<![CDATA[]]>

DIY Synth resources

<![CDATA[]]>Ray Wilson, Make: Analog Synthesizers<![CDATA[]]> <![CDATA[]]>Aaron Lanterman's class notes<![CDATA[]]>

Charles Julian Knight / Synthesizer - Files