Specifications

8 Starting with Pure Data
Objects
Here is a box
. A musical box, wound up a nd ready to play. We call these
boxes objects. Stuff goes in, stuff comes out. For it to pass into, or out of
them, objects must have inlets or outlets. Inlets are at the top of an object box,
outlets are at the bottom. Here is an object that has two inlets a nd one outlet:
. They are shown by small “tabs” on the edge of the object box. Objects
contain processes or procedures which change the things appearing at their
inlets and then send the results to one or more outlets. Each object performs
some simple function and has a name appearing in its box that identifies what
it does. There are two k inds of object, intrinsics which are pa rt of the core
Pd program, and externals which are separate files c ontaining add-ons to the
core functions. Collections of exter nals are called libraries and can be added to
extend the functionality of Pd. Most of the time you will neither know nor care
whether an object is intrinsic or external. In this book and elsewhere the words
process, function and unit are all occasionally used to refer to the object boxes
in Pd.
Connections
The connections between objects are sometimes called cords or wires. They
are drawn in a straight line between the outlet of one object and the inlet of
another. It is okay for them to cross, but you should try to avoid this since it
makes the patch diagram harder to read. At present there are two degrees of
thickness for cords. Thin ones carry message data and fatter ones carry audio
signals. Max/MSP
TM
and probably future versions of Pd will offer different
colours to indicate the data types carried by wir e s.
Data
The “stuff” being processed comes in several flavo urs, video frames, sound sig-
nals and messages. In this book we will only be concerned with sounds and
messages. O bjects give clues about what kind of data they proce ss by their
name. For example, an object that adds together two sound signals looks like
+~
. The + means this is an addition object, and the ∼ (tilde character) means
it object operates on signa ls. Objects without the tilde are used to process mes-
sages, which we shall concentrate on before studying audio signal processing.
Patches
A collection of objects wired together is a program or patch. For historical
reasons the words program and patch
2
are used to mean the same thing in
sound synthesis. Patches are an older way of describing a synthesiser built from
modular units connected together with patch cords. Because inlets and outlets
are at the top and bottom of objects the data flow is generally down the patch.
Some objects have mo re than one inlet or more than one outlet, so signals and
messages can be a function of many others and may in turn generate multiple
2
A different meaning of patch to the one programmers use to describe changes made to a
program to removes bugs