Copyright © 2011 by Denny Lin1 Simple Synthesizer Part 3 Based on Floss Manuals (Pure Data) “Building a Simple Synthesizer” By Derek Holzer Slides by Denny Lin

Copyright © 2011 by Denny Lin2 Filters Low Pass Filter: Allows frequencies below cutoff to pass through High Pass Filter: Allows frequencies above cutoff to pass through Band Pass Filter: Allows frequencies within a certain range to pass through; range is specified by its central frequency and its width is specified by the resonance value Voltage Controlled Filter: Similar to band pass filter, but the central frequency and resonance can be controlled by audio signals

Copyright © 2011 by Denny Lin3 Filters and Subtractive Synthesis Subtractive synthesis starts with a sound that is rich in harmonics, and then selectively subtract harmonics to get a desired sound Low pass, high pass, band pass, or voltage controlled filters can be used to remove undesirable harmonics, and the gain of the resulting waveforms can be modulated by an envelope generator

Copyright © 2011 by Denny Lin4 Phone voice using Subtractive Synthesis The frequency response of telephones is between 300Hz and 3000Hz Can reproduce the sound characteristics of a telephone by subtracting signals outside the telephone frequency response Effect of filter is intensified by placing filters in series (cascading)

Copyright © 2011 by Denny Lin5 Envelopes and generators Envelopes can be used to describe how a pitch or a sound amplitude changes over time An ADSR generator is often used to control sound amplitude changes of an oscillator The four components in an envelope generator are: –Attack –Decay –Sustain –Release Some older synthesizers added a Hold component: –ADSHR (Korg MS-20) –AHDSR ADSR generators can be made from both the line~ and vline~ objects Envelopes also be drawn and stored in arrays

Copyright © 2011 by Denny Lin6 Using the line~ generator The line and line~ objects take messages that have only two numbers: –Target level –Time in milliseconds New messages will over-ride a ramp in progress The audio version of the line object is line~ Can build ADSR envelopes when used with delay objects

Copyright © 2011 by Denny Lin7 ADSR Envelope and line~ messages AttackDecaySustainRelease A Gain D Gain A Delay D Delay A Time D Time S Time R Time Where D Elapsed = A Delay + A Time + D Delay and S Elapsed = D Elapsed + D Time + S Time A Gain A Time D Gain D Time 0 R Time A Delay D Elapsed S Elapsed trigger bang bang bang

Copyright © 2011 by Denny Lin8 An ADSR generator using line~

Copyright © 2011 by Denny Lin9 Using the vline~ generator The vline~ object has three inlets that take three parameters: –Target level –TIme in milliseconds –Delay value The left inlet can also take sequences of messages that contain target, time, and delay values. A sequence of messages can be used to specify an ADSR envelope The message: – , , –Ramp up to 0.8 in 1000ms after 5ms delay, ramp down to 0.5 in 1000ms after 1500ms delay, and ramp down to 0 in 500 ms after 3300ms delay All delay values are counted from the beginning of the message, so must take into account elapsed time performing previous instructions in the message

Copyright © 2011 by Denny Lin10 ADSR Envelope and vline~ message AttackDecaySustainRelease A Gain D Gain A Delay D Delay A Time D Time S Time R Time A Gain A Time A Delay, D Gain D Time D Elapsed, 0 R Time S Elapsed Where D Elapsed = A Delay + A Time + D Delay and S Elapsed = D Elapsed + D Time + S Time

Copyright © 2011 by Denny Lin11 An ADSR generator using vline~

Copyright © 2011 by Denny Lin12 Drawing and Storing an Envelope An envelope can be directly drawn by hand in an array graph This patch uses the line~ object to produce x-axis values from 0 to 99 in 4 seconds The audio envelope controls the amplitude of the oscillator

Copyright © 2011 by Denny Lin13 Controlling Sound Amplitude A slider can be used to control the gain when connected to the cold inlet of a multiplication object; output contains zipper noise Zipper noise can be eliminated using the line~ object Sound amplitude can be controlled by envelopes generated by line~, vline~, and read from an array by tabread4~