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State variable inside an expression
============================================================================================================================================
**04-let-function.py**
User can create state variable with the keyword `let`. This is
useful to set an intermediate state to be used in multiple places
in the processing chain. The syntax is:
.. code-block:: scheme
(let #var (body))
The variable name must begin with a `#`.
The prefix expression `documentation`_ gives common use cases where we
may want to use state variables.
.. _documentation: http://ajaxsoundstudio.com/pyodoc/api/classes/expression.html
The following example implements a phase-aligned formant (PAF) generator, as
described by Miller Puckette in "The Theory and Technique of Electronic
Music", p158.
.. code-block:: python
from pyo import *
s = Server().boot()
expression = """// PAF generator (single formant) //
// User variables
(let #fund 100) // fundamental frequency
(let #band 600) // formant bandwidth
(let #form 600) // formant center frequency
// Intermediate variables
(let #bw (/ #band #fund))
(let #cf (/ #form #fund))
(let #ph (* (- (~ #fund) 0.5) twopi))
(let #car ( // Carrier
(cos (max (min (* #ph #bw) pi) (- 0 pi)))
)
)
(let #mod ( // Modulator
(let #oct (floor #cf))
(let #frac (% #cf 1))
(+ (* (cos (* #ph #oct)) (- 1 #frac))
(* (cos (* #ph (+ #oct 1))) #frac)
)
)
)
* (* #car #mod) 0.5
"""
expr = Expr(Sig(0), expression, mul=0.5)
expr.editor()
sp = Spectrum(expr)
pan = Pan(expr).out()
s.gui(locals())
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