03-exponential-ramp.py - Exponential portamento with rising and falling times.
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The Port object is designed to lowpass filter an audio signal with
different coefficients for rising and falling signals. A lowpass
filter is a good and efficient way of creating an exponential ramp
from a signal containing abrupt changes. The rising and falling
coefficients are controlled in seconds.

.. code-block:: python

    from pyo import *
    
    s = Server().boot()
    
    # 2 seconds linear ramp starting at 0.0 and ending at 0.3.
    amp = SigTo(value=0.3, time=2.0, init=0.0)
    
    # Pick a new value four times per second.
    pick = Choice([200, 250, 300, 350, 400], freq=4)
    
    # Print the chosen frequency
    pp = Print(pick, method=1, message="Frequency")
    
    # Add an exponential portamento on an audio target and detune a second frequency.
    # Sharp attack for rising notes and long release for falling notes.
    freq = Port(pick, risetime=0.001, falltime=0.25, mul=[1, 1.005])
    # Play with portamento times.
    freq.ctrl()
    
    # Play a simple wave.
    sig = RCOsc(freq, sharp=0.7, mul=amp).out()
    
    s.gui(locals())