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<H3>Instrument Declarations</H3>
<B>Tao</B> provides a set of classes for creating pieces of the material described
in section <A HREF="UserManual_20.html">*</A>. Each class deals with a creating
a piece of material of a particular geometrical shape, so for example the
user can create strings, circular sheets, rectangular sheets and
elliptical sheets. The way in which <B>Tao</B>'s cellular material is actually
implementated provides for future support of irregularly shaped
components but in the present version the user is limited to these
geometrical primitives.
<P>In practice though this is not a serious limitation since there are
many other techniques available for designing interesting instruments.
These include damping and locking parts of an instrument and constructing
<EM>compound instruments</EM><A NAME="1"> by</A> coupling several pieces of material together
using Connector devices. All of these techniques provide ample
room for experimentation.
<P>In order to create a <EM>primitive</EM> instrument
several pieces of information are required.
These include the instrument type, the name by which it will be referred
to in the script, its <I>x</I> and <I>y</I> frequencies, and its decay time.
<P>The general form of an instrument declaration is illustrated by the
following string declaration:
<P><PRE>
String string(<pitch>, <decay_time>);
</PRE>
<P>where <CODE>String</CODE> is the name of the instrument class; <CODE>string</CODE>
is the name of the particular instrument being created;
<CODE><pitch></CODE> defines (indirectly) how long the string will be
(the tension in <B>Tao</B>'s material cannot be altered so the length of a string
is related to its pitch or frequency alone and vice versa); and
<CODE><decay_time></CODE> determines the amplitude decay time of the instrument.
<P>In the next example the placeholders <CODE><pitch></CODE> and <CODE><decay_time></CODE>
are replaced with typical values which might occur in a script:
<P><PRE>
String string(C#5+1/2, 4.5 secs);
</PRE>
<P>In this example the length of the string is set such that its pitch
is C sharp plus a quarter-tone (1/2 a semitone) in octave 5, and
its decay time is four and a half seconds.
The <CODE><pitch></CODE> argument can be specified in a number of different
formats, some of which are directly analogous to those provided in
Csound. The other formats are introduced throughout this section
by way of example. The format used in the example above is referred to
as <EM>note name format</EM><A NAME="2"> format.</A>
<P>The <CODE><decay_time></CODE> argument consists of a numerical constant
followed by the units of time, i.e. <CODE>sec</CODE>, <CODE>secs</CODE>, <CODE>min</CODE>,
<CODE>mins</CODE> or <CODE>msecs</CODE>, representing seconds, minutes and milliseconds
respectively.
<P>A second practical example is given below, this time creating a
rectangular sheet called <CODE>rect</CODE>:
<P><PRE>
Rectangle rect(200 Hz, 500 Hz, 60 secs);
</PRE>
<P>In this example two pitch arguments are specified, and both are given
in <EM>frequency format</EM><A NAME="3">.</A> The first
determines the size of the instrument in the <I>x</I> direction and
the second, the size in the <I>y</I> direction. It may seem slightly
unintuitive at first to be specifying the size of a rectangular
sheet in units of Hertz rather than physical dimensions such
as metres or millimetres, but this practice is adopted
for a number of good reasons:
<P><OL><LI>It makes creating precisely pitched instruments a simpler matter;
<LI><B>Tao</B>'s material is not based upon any real-world material so
it would be meaningless to talk about a sheet of cellular material 5m by 3.5m;
<LI>The instrument is described in units which are of more perceptual
relevance to a musician than physical units of size (open to debate).
</OL>
<P>Another advantage of specifying dimensions by pitch or frequency is that it
becomes a simple matter to construct an instrument which has an array of
similar components but with different pitches for each. For example the
following code fragment creates a set of rectangular components with uniform
<I>y</I> dimension but pitches tuned to fractions of an octave for the
<I>x</I> dimension. This kind of instrument might be the starting point
for some sort of pitched percussion instrument for example:
<P><PRE>
Rectangle rect1(8.0 oct, 500 Hz, 60 secs);
Rectangle rect2(8.2 oct, 500 Hz, 60 secs);
Rectangle rect3(8.4 oct, 500 Hz, 60 secs);
Rectangle rect4(8.6 oct, 500 Hz, 60 secs);
Rectangle rect5(8.8 oct, 500 Hz, 60 secs);
Rectangle rect6(9.0 oct, 500 Hz, 60 secs);
</PRE>
<P>This example shows yet another form of the pitch argument, i.e.
<EM>octave/fraction format</EM><A NAME="4">
or</A> <CODE>oct</CODE> format for short. In this format the integer part specifies
the octave and the fractional part after the decimal point specifies a
fraction of an octave.
<P>The previous example opens the way for describing another important
technique often used when creating instruments with arrays of similar components.
<B>Tao</B> provides an <EM>array</EM><A NAME="5"> facility</A> for grouping
together such components and giving them a common name. For example
the following script code has much the same effect as the previous example
but logically groups the six rectangular components together into an
array with a single name <CODE>rect_array</CODE>:
<P><PRE>
Rectangle rect_array[6]=
{
(8.0 oct, 500 Hz, 60 secs),
(8.2 oct, 500 Hz, 60 secs),
(8.4 oct, 500 Hz, 60 secs),
(8.6 oct, 500 Hz, 60 secs),
(8.8 oct, 500 Hz, 60 secs),
(9.0 oct, 500 Hz, 60 secs)
};
</PRE>
<P>The individual components can be accessed using syntax which will be very
familiar to C and C++ programmers:
<P><PRE>
rect_array[0], rect_array[1] .. rect_array[5]
</PRE>
<P>The declarations for circular, elliptical and triangular sheets of material
follow a similar format to the examples presented in this section, with
elliptical and triangular sheets requiring two pitch values and circular
sheets requiring only one (determining the diameter).
<P>Examples are given below:
<P><PRE>
Circle circle(5.03 pch, 20 secs)
Ellipse ellipse(6.00 pch, 50 Hz, 1 min + 20 secs)
Triangle triangle(100 Hz, 6.5 oct, 600 msecs)
</PRE>
<P>These declarations introduce the final pitch notation,
<EM>octave/semitone format</EM><A NAME="6">
or</A> <CODE>pch</CODE> format for short. In this format the fractional part after
the decimal point is interpreted as semitones. For example <CODE>5.03 pch</CODE>
means the third semitone above C in octave 5. Note that fractions of
semitones are also possible. For example <CODE>5.035 pch</CODE> means 3.5
semitones above C in octave 5.
<P>Note also that the different pitch formats can be used side by side
in an instrument declaration requiring more than one pitch.
<P>
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<tr><td colspan="3" class="addr"><!-- bottom panel --><ADDRESS><FONT SIZE=-1>©1999,2000 Mark Pearson
<A HREF="mailto:m.pearson@ukonline.co.uk">m.pearson@ukonline.co.uk</A> April 30, 2000</ADDRESS><BR></td></tr><!-- end bottom panel --></table></BODY></HTML>
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