copyright © 2011 by denny lin1 simple synthesizer part 4 based on floss manuals (pure data)...

Copyright © 2011 by Denny Lin 1

Simple Synthesizer Part 4

Based on Floss Manuals (Pure Data)“Building a Simple Synthesizer”

By Derek HolzerSlides by Denny Lin


Controlling the Synthesizer

• Two ways for synthesizer and user interface:– Input from computer keyboard. The ASCII

value of the key pressed is gathered by the key object, which converts its into frequency values using the mtof object

– Input from MIDI keyboard. Reads the note number and velocity from channel 1 using the notein 1 object.


Building a 16-Step Sequencer

• Consists of a:– Constrained counter– MIDI note storage and

retrieval– Simple subtractive

synthesizer with ADSR envelope to play back notes


A Four Stage Filtered Additive Synthesizer

• Consists of the following stages:– Input– Oscillator– Filter– Amplifier

• These four stages are contained in sub-patches


Input Stage

• The key object gets the ASCII value of the key pressed on the computer keyboard

• ASCII value is sent to left most outlet

• Center outlet sends the same ASCII value as the left most outlet

• Right most outlet sends a bang used by the ADSR generator


Oscillator Stage

• Takes the midi number and converts it to a frequency used by the two phasor~ objects

• Second phasor~ object has slightly de-tuned pitch (input is multiplied by 0.99 –almost one--)

• Output is added, and scaled down to 0.5 before delivering to the audio outlet


Filter Stage

• Uses a Voltage Controlled Filter to perform subtractive synthesis.

• The VCO’s center frequency is set to 1.5 times (half an octave) above the incoming audio signal

• The center frequency is packed and sent to the line~ object, so it ramps to the center frequency in 300ms

• The ramp from the line~ object creates a filter sweeping effect


Amplifier Stage

• The amplitude of the audio signal is modified by the ADSR envelope

• Controls the overall volume of the signal coming in from the Filter Stage

• Output is sent to the audio outlet


The poly object

• The poly object assigns a voice number to a pitch and velocity pair

• poly object creation arguments:– First: Number of voices– Second: Voice stealing mode (what to do

when input exceeds number of voices)• 0 = no voice stealing; ignore new note event• 1 = turns off oldest voice stored to make space for

new note event


Building a polyphonic synthesizer

• Use the notein object to extract pitch and velocity pairs from the MIDI data stream

• Assign a voice number to pitch and velocity pairs with the poly object

• Pack the voice number, pitch, and velocity information into a list• Route the list by voice number to multiple oscillators. Must have one

oscillator for each voice. Can filter each voice individually, or as a group

• The next example filters voices individually, because each voice has a filter that sweeps to a unique pitch for that voice. To minimize control lines, the filter is built into the oscillator

• Polyphonic output amplitude can be modified by an ADSR envelope and amplified


A polyphonic MIDI synthesizer

Based on Benoît Rouits’ “A Real Polyphonic MIDI Organ” http://puredata.info/author/ben

copyright © 2011 by denny lin1 simple synthesizer part 4 based on floss manuals (pure data)...

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