Manipulating audio signal in input

The expression illustrated in this example use a phasor signal in input as the running phase of a self-modulated sine wave.

Here is the complete expression:

(sin (+ (* twopi $x[0]) (* $y[-1] 0.8)))

From inner to outer expression, we have:

(* $y[-1] 0.8)

Where $y[-1] is the last output sample multiplied by a feedback factor (0.8). Then we have the running phase, $x[0] is the current input sample, rescaled to the range 0 -> 2pi for the sin function:

(* twopi $x[0])

We add the output delay to the running phase:

(+ (* twopi $x[0]) (* $y[-1] 0.8))

This gives the modulated running phase driving the sin function:

(sin (+ (* twopi $x[0]) (* $y[-1] 0.8)))

Complete example

from pyo import *

s = Server().boot()

expression = """
// Self-modulated sine wave with running phase given in input.
// Try different feedback factors between 0 and 1.
(sin (+ (* twopi $x[0]) (* $y[-1] 0.8)))

# External signal used as the running phase.
input = Phasor(86)

# Create the Expr object and show its expression editor. To
# re-evaluate the expression hit Ctrl+Enter when the editor
# has the focus.
expr = Expr(input, expression, mul=0.5)

# Shows the generated signal.
sc = Scope(expr)

# Converts the mono signal to stereo and sends it to the soundcard.
pan = Pan(expr).out()