Another tutorial about creating a custom PyoObject (Flanger)

There are few steps we need to take care of in order to create a class with all of the PyoObject behaviors.

Things to consider:

  • The parent class must be PyoObject, that means the PyoObject’s __init__ method must be called inside the object’s __init__ method to properly initialize PyoObject’s basic attributes.
  • When a PyoObject receives another PyoObject, it looks for a list of objects called “self._base_objs”. This list must contain the C implementation of the audio objects generating the output sound of the process.
  • Adding “mul” and “add” arguments (they act on objects in self._base_objs).
  • All PyoObjects support “list expansion”.
  • All PyoObjects with sound in input support cross-fading between old and new sources.
  • We will probably want to override the play(), out() and stop() methods.
  • There is an attribute for any function that modify a parameter.
  • We should override the ctrl() method to allow a GUI to control parameters.

In this tutorial, we will define a Flanger object with this definition:

Flanger(input, depth=0.75, lfofreq=0.2, feedback=0.25, mul=1, add=0)

First of all, we need to import the pyo module

from pyo import *

Step 1 - Declaring the class

We will create a new class called Flanger with PyoObject as its parent class. Another good habit is to put a __doc__ string at the beginning of our classes. Doing so will allow other users to retrieve the object’s documentation with the standard python help() function.

class Flanger(PyoObject):
    """
    Flanging effect.

    A flanging is an audio effect produced by mixing two identical signals together,
    with one signal delayed by a small and gradually changing period, usually smaller
    than 20 milliseconds. This produces a swept comb filter effect: peaks and notches
    are produced in the resultant frequency spectrum, related to each other in a linear
    harmonic series. Varying the time delay causes these to sweep up and down the
    frequency spectrum.


    :Parent: :py:class:`PyoObject`

    :Args:

        input : PyoObject
            Input signal to process.
        depth : float or PyoObject, optional
            Amplitude of the delay line modulation, between 0 and 1.
            Defaults to 0.75.
        lfofreq : float or PyoObject, optional
            Frequency of the delay line modulation, in Hertz.
            Defaults to 0.2.
        feedback : float or PyoObject, optional
            Amount of output signal reinjected into the delay line.
            Defaults to 0.25.

    >>> s = Server().boot()
    >>> s.start()
    >>> inp = SfPlayer(SNDS_PATH + "/transparent.aif", loop=True)
    >>> lf = Sine(0.005, mul=0.25, add=0.5)
    >>> flg = Flanger(input=inp, depth=0.9, lfofreq=0.1, feedback=lf).out()

    """

Step 2 - The __init__ method

This is the place where we have to take care of some of pyo’s generic behaviours. The most important thing to remember is that when a PyoObject receives another PyoObject in input, it looks for an attribute called self._base_objs. This attribute is a list of the object’s base classes and is considered the audio output signal of the object (the Sine object uses internally an object called Sine_base). The getBaseObjects() method returns the list of base classes for a given PyoObject. We will call the getBaseObjects() method on the objects generating the output signal of our process. .play(), .out(), .stop() and .mix() methods act on this list.

We also need to add two arguments to the definition of the object: “mul” and “add”. The attributes “self._mul” and “self._add” are handled by the parent class and are automatically applied to the objects stored in the list “self._base_objs”.

Finally, we have to consider the “multi-channel expansion” feature, allowing lists given as arguments to create multiple instances of our object and managing multiple audio streams. Two functions help us to accomplish this:

convertArgsToLists(*args) : Return arguments converted to lists and the maximum list size. wrap(list,i) : Return value at position “i” in “list” with wrap around len(list).

def __init__(self, input, depth=0.75, lfofreq=0.2, feedback=0.5, mul=1, add=0):
    # Properly initialize PyoObject's basic attributes
    PyoObject.__init__(self)

    # Keep references of all raw arguments
    self._input = input
    self._depth = depth
    self._lfofreq = lfofreq
    self._feedback = feedback

    # Using InputFader to manage input sound allows cross-fade when changing sources
    self._in_fader = InputFader(input)

    # Convert all arguments to lists for "multi-channel expansion"
    in_fader, depth, lfofreq, feedback, mul, add, lmax = convertArgsToLists(
                            self._in_fader, depth, lfofreq, feedback, mul, add)

    # Apply processing
    self._modamp = Sig(depth, mul=0.005)
    self._mod = Sine(freq=lfofreq, mul=self._modamp, add=0.005)
    self._dls = Delay(in_fader, delay=self._mod, feedback=feedback)
    self._flange = Interp(in_fader, self._dls, mul=mul, add=add)

    # self._base_objs is the audio output seen by the outside world!
    self._base_objs = self._flange.getBaseObjects()

Step 3 - setXXX methods and attributes

Now, we will add methods and attributes getter and setter for all controllable parameters. It should be noted that we use the setInput() method of the InputFader object to change an input source. This object implements a cross-fade between the old source and the new one with a cross-fade duration argument. Here, we need to keep references of raw argument in order to get the real current state when we call the dump() method.

def setInput(self, x, fadetime=0.05):
    """
    Replace the `input` attribute.

    :Args:

        x : PyoObject
            New signal to process.
        fadetime : float, optional
            Crossfade time between old and new input. Defaults to 0.05.

    """
    self._input = x
    self._in_fader.setInput(x, fadetime)

def setDepth(self, x):
    """
    Replace the `depth` attribute.

    :Args:

        x : float or PyoObject
            New `depth` attribute.

    """
    self._depth = x
    self._modamp.value = x

def setLfoFreq(self, x):
    """
    Replace the `lfofreq` attribute.

    :Args:

        x : float or PyoObject
            New `lfofreq` attribute.

    """
    self._lfofreq = x
    self._mod.freq = x

def setFeedback(self, x):
    """
    Replace the `feedback` attribute.

    :Args:

        x : float or PyoObject
            New `feedback` attribute.

    """
    self._feedback = x
    self._dls.feedback = x

@property
def input(self):
    """PyoObject. Input signal to process."""
    return self._input
@input.setter
def input(self, x):
    self.setInput(x)

@property
def depth(self):
    """float or PyoObject. Amplitude of the delay line modulation."""
    return self._depth
@depth.setter
def depth(self, x):
    self.setDepth(x)

@property
def lfofreq(self):
    """float or PyoObject. Frequency of the delay line modulation."""
    return self._lfofreq
@lfofreq.setter
def lfofreq(self, x):
    self.setLfoFreq(x)

@property
def feedback(self):
    """float or PyoObject. Amount of out sig sent back in delay line."""
    return self._feedback
@feedback.setter
def feedback(self, x):
    self.setFeedback(x)

Step 4 - The ctrl() method

The ctrl() method of a PyoObject is used to pop-up a GUI to control the parameters of the object. The initialization of sliders is done with a list of SLMap objects where we can set the range of the slider, the type of scaling, the name of the attribute linked to the slider and the initial value. We will define a default “self._map_list” that will be used if the user doesn’t provide one to the parameter “map_list”. If the object doesn’t have any parameter to control with a GUI, this

def ctrl(self, map_list=None, title=None, wxnoserver=False):
    self._map_list = [SLMap(0., 1., "lin", "depth", self._depth),
                      SLMap(0.001, 20., "log", "lfofreq", self._lfofreq),
                      SLMap(0., 1., "lin", "feedback", self._feedback),
                      SLMapMul(self._mul)]
    PyoObject.ctrl(self, map_list, title, wxnoserver)

Step 5 - Overriding the .play(), .stop() and .out() methods

Finally, we might want to override .play(), .stop() and .out() methods to be sure all our internal PyoObjects are consequently managed instead of only objects in self._base_obj, as it is in built-in objects. To handle properly the process for self._base_objs, we still need to call the method that belongs to PyoObject. We return the returned value (self) of these methods in order to possibly append the method to the object’s creation. See the definition of these methods in the PyoObject man page to understand the meaning of arguments.

def play(self, dur=0, delay=0):
    self._modamp.play(dur, delay)
    self._mod.play(dur, delay)
    self._dls.play(dur, delay)
    return PyoObject.play(self, dur, delay)

def stop(self):
    self._modamp.stop()
    self._mod.stop()
    self._dls.stop()
    return PyoObject.stop(self)

def out(self, chnl=0, inc=1, dur=0, delay=0):
    self._modamp.play(dur, delay)
    self._mod.play(dur, delay)
    self._dls.play(dur, delay)
    return PyoObject.out(self, chnl, inc, dur, delay)

Here we are, we’ve just created our second custom pyo object!

Complete class definition and test

from pyo import *

class Flanger(PyoObject):
    """
    Flanging effect.

    A flanging is an audio effect produced by mixing two identical signals together,
    with one signal delayed by a small and gradually changing period, usually smaller
    than 20 milliseconds. This produces a swept comb filter effect: peaks and notches
    are produced in the resultant frequency spectrum, related to each other in a linear
    harmonic series. Varying the time delay causes these to sweep up and down the
    frequency spectrum.


    :Parent: :py:class:`PyoObject`

    :Args:

        input : PyoObject
            Input signal to process.
        depth : float or PyoObject, optional
            Amplitude of the delay line modulation, between 0 and 1.
            Defaults to 0.75.
        lfofreq : float or PyoObject, optional
            Frequency of the delay line modulation, in Hertz.
            Defaults to 0.2.
        feedback : float or PyoObject, optional
            Amount of output signal reinjected into the delay line.
            Defaults to 0.25.

    >>> s = Server().boot()
    >>> s.start()
    >>> inp = SfPlayer(SNDS_PATH + "/transparent.aif", loop=True)
    >>> lf = Sine(0.005, mul=0.25, add=0.5)
    >>> flg = Flanger(input=inp, depth=0.9, lfofreq=0.1, feedback=lf).out()

    """
    def __init__(self, input, depth=0.75, lfofreq=0.2, feedback=0.5, mul=1, add=0):
        PyoObject.__init__(self)
        self._input = input
        self._depth = depth
        self._lfofreq = lfofreq
        self._feedback = feedback
        self._in_fader = InputFader(input)
        in_fader, depth, lfofreq, feedback, mul, add, lmax = convertArgsToLists(
                                self._in_fader, depth, lfofreq, feedback, mul, add)

        self._modamp = Sig(depth, mul=0.005)
        self._mod = Sine(freq=lfofreq, mul=self._modamp, add=0.005)
        self._dls = Delay(in_fader, delay=self._mod, feedback=feedback)
        self._flange = Interp(in_fader, self._dls, mul=mul, add=add)

        self._base_objs = self._flange.getBaseObjects()

    def setInput(self, x, fadetime=0.05):
        """
        Replace the `input` attribute.

        :Args:

            x : PyoObject
                New signal to process.
            fadetime : float, optional
                Crossfade time between old and new input. Defaults to 0.05.

        """
        self._input = x
        self._in_fader.setInput(x, fadetime)

    def setDepth(self, x):
        """
        Replace the `depth` attribute.

        :Args:

            x : float or PyoObject
                New `depth` attribute.

        """
        self._depth = x
        self._modamp.value = x

    def setLfoFreq(self, x):
        """
        Replace the `lfofreq` attribute.

        :Args:

            x : float or PyoObject
                New `lfofreq` attribute.

        """
        self._lfofreq = x
        self._mod.freq = x

    def setFeedback(self, x):
        """
        Replace the `feedback` attribute.

        :Args:

            x : float or PyoObject
                New `feedback` attribute.

        """
        self._feedback = x
        self._dls.feedback = x

    def play(self, dur=0, delay=0):
        self._modamp.play(dur, delay)
        self._mod.play(dur, delay)
        self._dls.play(dur, delay)
        return PyoObject.play(self, dur, delay)

    def stop(self):
        self._modamp.stop()
        self._mod.stop()
        self._dls.stop()
        return PyoObject.stop(self)

    def out(self, chnl=0, inc=1, dur=0, delay=0):
        self._modamp.play(dur, delay)
        self._mod.play(dur, delay)
        self._dls.play(dur, delay)
        return PyoObject.out(self, chnl, inc, dur, delay)

    def ctrl(self, map_list=None, title=None, wxnoserver=False):
        self._map_list = [SLMap(0., 1., "lin", "depth", self._depth),
                          SLMap(0.001, 20., "log", "lfofreq", self._lfofreq),
                          SLMap(0., 1., "lin", "feedback", self._feedback),
                          SLMapMul(self._mul)]
        PyoObject.ctrl(self, map_list, title, wxnoserver)

    @property
    def input(self):
        """PyoObject. Input signal to process."""
        return self._input
    @input.setter
    def input(self, x):
        self.setInput(x)

    @property
    def depth(self):
        """float or PyoObject. Amplitude of the delay line modulation."""
        return self._depth
    @depth.setter
    def depth(self, x):
        self.setDepth(x)

    @property
    def lfofreq(self):
        """float or PyoObject. Frequency of the delay line modulation."""
        return self._lfofreq
    @lfofreq.setter
    def lfofreq(self, x):
        self.setLfoFreq(x)

    @property
    def feedback(self):
        """float or PyoObject. Amount of out sig sent back in delay line."""
        return self._feedback
    @feedback.setter
    def feedback(self, x):
        self.setFeedback(x)

# Run the script to test the Flanger object.
if __name__ == "__main__":
    s = Server().boot()
    src = BrownNoise([.2,.2]).out()
    fl = Flanger(src, depth=.9, lfofreq=.1, feedback=.5, mul=.5).out()
    s.gui(locals())