# Manipulating audio signal in input¶

02-audio-in.py

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)
input.ctrl()

# 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)
expr.editor()

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

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

s.gui(locals())
```