Copyright © 2011 by Denny Lin1 Computer Music Synthesis Chapter 2 Based on “Excerpt from...

Copyright © 2011 by Denny Lin 1

Computer Music Synthesis

Chapter 2Based on “Excerpt from Designing Sound”

by Andy FarnellSlides by Denny Lin


Starting with Pure Data

• 2.1 Pure Data

• 2.2 How does Pure Data work?

• 2.3 Message data and GUI boxes

• 2.4 Getting help with Pure Data


2.1 Pure Data

• Pure Data (Pd) is a visual signal dataflow programming language

• Designed to process sound and MIDI events. Has grown to process video and inputs from a variety of general purpose sensors

• Free alternative to MAX/MSP• Runs on Linux, Macintosh, and Windows

computers


Pure Data Console


Pure Data Test Signal


2.2 How does Pure Data work?

• Data flows between objects connected through cords or wires

• Thin cords carry message data; fat cords carry audio signals

• Objects take in data at inlets, and may send output to outlets; inlets and outlets appear as tabs at the edge of objects

• Types of object names:– Object names with ~: Process signals– Object names without ~: Process messages


Patches

• A collection of objects wired together is a dataflow graph program or patch. Name is derived from analog electronic synthesizer modules connected together with patch cords

• Patches are placed on a canvas• Patches are navigated by the PD interpreter

depth first, from right to left (tries to go as deep as possible in a graph, processing the right-most branch first before a left branch)


Dataflow computation


Pure Data Software Architecture

• Pure Data consists of several programs:– pd(main engine): the interpreter, scheduler and audio engine– pd-gui: the interface you use to build Pure Data programs– pd-watchdog: monitors the main engine and gui, and will attempt

to terminate unresponsive pd or pd-gui


Some Command Shortcuts

• CTRL+1: Put object• CTRL+3: Put number• CTRL+A: Select all objects on canvas• CTRL+C: Copy selection • CTRL+D: Duplicate selection• CTRL+E: Toggle Edit Mode• CTRL+O: Open file• CTRL+S: Save file• CTRL+V: Paste selection• CTRL+X: Cut selection• SHIFT: Select multiple objects


Placing a new object

• Can use Put->Object from menu, or use CTRL+1• An active dotted box (object) appears• Assign a name to the object• Depending on the object’s name, Pd assigns an

appropriate number of inlets and outlets, changing the dotted box into a solid box; no changes and assignments made to unrecognized objects

• To delete an object, click and hold to draw a selection box around the target object, and press delete


Wiring

• Hovering over an outlet changes the mouse cursor to a wiring tool

• Click and hold the mouse when the wiring tool is active, and drag a connection from the first object; hover over another compatible object and release the mouse to complete a connection

• To delete a connection, click on a connection to select it and press delete


Initial Parameters or Arguments

• Most objects can take default initial values, which are specified as initial parameters or arguments

• These parameters are not always required

• Uninitialized values generally are set to 0

Add a 3 to its input by defaultAddition depends on inlet(s)


Modifying Objects

• The name and function of an object, and its parameters can be changed

• The following causes the multiply object to always multiply its input by 5, and the addition object to always add 3 to its input.

• When 4 is the input of the multiply object, the output of the graph is (4 x 5) + 3 = 23


Number Input and Output

• Number boxes can be used to enter numbers, or view results

• Can use Put->Number from the menu or use CTRL+3

• The following solves y = 5x + 3, where x = 10


Toggle Edit Mode

• In edit mode, you can move or modify objects• To use the patch, you must exit edit mode• Pressing CTRL+E (or Edit->Edit from menu)

allows you to enter and exit edit mode• While not in edit mode, place the mouse on the

top number box (fig. 2.9), then drag the mouse up and down; this changes the computed result in the second number box


More Edit Operations

• Objects can be copied into the buffer using familiar cut, copy, paste, and duplicate commands

• Select multiple objects by holding Shift while clicking on targets

• Duplicating groups of objects will also duplicate connections between them


Patch Files

• Pd files are text files that end with a .pd file extension

• Novices should avoid modifying these text files

• Can use File->Save or CTRL+S to save the current canvas

• Can use File->Open or CTRL+O to load a patch file


2.3 Message data and GUI boxes

• Messages are events or data sent between two objects

• A message can be:– as short as a character or a number, or– as long as an entire musical score or synthesizer

parameter set• GUI boxes (objects) can be placed on a canvas

using the Put menu, or using CTRL+1 through CTRL+8

• All GUI boxes have properties that can be modified (in edit mode) by clicking on them and selecting the properties pop-up menu item


Selectors

• All messages (except bang) carry an invisible selector that identifies the message type (symbol, number, pointer, or list)

• When a message arrives at the inlet of an object, the object examines the selector to see if it has an appropriate method to handle the message

• If the object does not have an appropriate method, an error message reports the incompatible data type


Bang message and box

• The most fundamental and smallest message• The bang is used to cause an object to output a

value or advance to a next state• Other messages have an implicit bang• A bang box sends and receives messages;

changes from white to black whenever it sends or receives a bang

• Bang boxes can be used to initiate actions or as indicators


Float messages and Number boxes

• All numbers (even integers) are stored as 32 bit floating point values in Pd

• A number box object has a beveled top right corner• Number box values can be changed by using the mouse:

– Coarse control: drag the mouse up or down over the value field– Fine control: hold shift while dragging the mouse up or down

• Number boxes display by default up to 5 digits including a sign (-9999 to 99999). Can be changed in the properties dialog


Toggle box

• Toggle boxes work with floats to represent on and off states. When clicked, a cross appears in the box, and a number 1 is sent. When the box is clear, a 0 is sent

• Sending a bang to the inlet of a toggle box flips the toggle box to an opposite state

• Other non-zero values can be sent by editing the properties dialog


Sliders and other numerical GUI elements

• GUI elements for horizontal and vertical sliders can be used as input and display elements; has a default range of 0 to 127

• Radio boxes provide mutually exclusive buttons which output a number starting at zero; can be used either as indicators or input elements

• VU meters can be used to indicate decibels (scale of -99.0 to +12.0), and can be used only as display (output) element


Message box

• Visual containers for user definable messages

• Only has one inlet and one outlet

• When clicked or when a bang is received, its contents are sent to the outlet

• Is aware of the type of data it stores, and will output data of matching type


Symbolic messages

• A symbol is usually a word or some text, and can contain any printable or non-printable character

• Whitespace is used to separate symbols from each other: cannot type a symbol that has a space character in a message box

• Valid symbols:– Badget, sound_2, or all_your_base

• Invalid symbols:– Hello there (there are two symbols)– 20 (interpreted as float 20.0)


Symbol box

• The symbol box displays text, or can be used to input

• Enter a valid symbol text, and a symbol message will be sent to the outlet

• A symbol message received at the inlet will be displayed as text

• Sending a bang message to a symbol box causes it to output its contents


Lists

• A list is an ordered collection of floats, symbols, pointers, or any things

• This collection is treated as one set• Lists have a list selector attached to the

beginning of its message• Lists may contain mixed types:

– {5 6 pick up sticks} contains two floats and three symbols

• A list of one float will be type cast to a float


Tables, arrays and graphs

• A table is a way of using an array, and is a two-dimensional data structure

• Arrays are invisible

• A graph can be used to view array contents


Creating a new array• Use Put->Array from the menu,

and complete the dialog box to set up the array name, size, and display characteristics

• The Save contents option stores array data with the patch file

• The points, polygon, Bezier curve show data with different degrees of smoothing

• Can put more than one array in same graph to compare two or more sets of data, by selecting the last graph option

• The tabwrite object writes data to array

• The tabread object reads data from array


Tabwrite and Tabread

• Tabwrite takes the array name as its parameter, and writes data to array– Right inlet sets the index– Left inlet sets the value

• Tabread takes the array name as its parameter, and reads data from the array– The inlet specifies the index– The outlet returns the array’s value


2.3 Getting help with Pure DataOriginal PD Documentation• http://www.crca.ucsd.edu/~msp/Pd_documentation/index.htm

Online PD Users Forum• http://puredata.hurleur.com

Tutorials• http://www.pd-tutorial.com/english/index.html• http://obiwannabe.co.uk/tutorials/html/tutorials_main.html

Textbooks used in MUET495• http://aspress.co.uk/ds/pdf/pd_intro.pdf• http://en.flossmanuals.net/PureData/_booki/pure-data/pure-data.pdf

http://www.crca.ucsd.edu/~msp/Pd_documentation/index.htm

http://www.crca.ucsd.edu/~msp/Pd_documentation/index.htm

http://puredata.hurleur.com/

http://www.pd-tutorial.com/english/index.html

http://obiwannabe.co.uk/tutorials/html/tutorials_main.html

http://aspress.co.uk/ds/pdf/pd_intro.pdf

http://aspress.co.uk/ds/pdf/pd_intro.pdf

http://en.flossmanuals.net/PureData/_booki/pure-data/pure-data.pdf

Copyright © 2011 by Denny Lin1 Computer Music Synthesis Chapter 2 Based on “Excerpt from...

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