Somewhere between the realms of oscilloscopes and player pianos lies a radical music instrument called Pure Data, or PD. You can hear what sorts of things Pure Data can do at the Pure Data Exhibition page.
Hopefully this article will make it very easy for newbies to get into PDing and I encourage anyone and everyone to give it a shot. On the other hand, it will require patience and lots of active thought. Lots of active thought. In fact, background knowledge of general mathematical algorithms would be very helpful for first time Pure Data enthusiast. Pure Data is ridiculously in-depth. If you are at all familiar with programming it will make sense to you. If not, do not fret; Pure Data is simple enough (in my opinion) that one can create some really cool stuff with not very much effort or prior programming knowledge. This is not to say that Pure Data can be seriously confusing and frustrating at times, but the payoff is very, very rewarding and, at times, very surprising.
Also, this article will not focus on obtaining and installing Pure Data. The installation process is self-explanatory enough that it should be easy for most computer users to install properly. If this is not the case, there is a vast number of resources available on the Pure Data community site that can assist in this.
Anyway, let’s get on with it.
Pure Data
As stated on Pure Data’s website:
Pd (aka Pure Data) is a real-time graphical programming environment for audio, video, and graphical processing.
In other words, Pure Data allows you create and modify images and sounds using “objects” organized in such a way that can closely resemble a flow chart. I use Pure Data for audio processing.
Diving into Pure Data
I am going to assume that you have properly installed audio drivers. Mac OS X has CoreAudio installed by default and this is perfectly acceptable for low-latency music creation. Windows and Ubuntu are a little less fortunate right off the bat. Windows has the wonderful ASIO emulation drivers ASIO4ALL, though if this is not your cup of tea, you can get by with the basic (and slow) Windows drivers. In the Linux realm, there exists a flavor of Ubuntu made explicitly for multimedia purposes called Ubuntu Studio. I have no experience with this distribution, therefore I cannot provide support for this. Again, you can find most information you need at the Pure Data community site.
Let’s get started.
The Main Window
Upon running Pure Data, you’ll notice the main window appear on your screen.
This window will run at all times and provides valuable output related to errors and other program output.
Edit mode and run mode
As you work with Pure Data, you will be using two modes available in the program. Edit mode allows you to add, remove and modify objects, messages, numbers, etc. in your Pure Data patch. When you switch to run mode (by pressing Control-E in Windows/Linux or Command-E in Mac, or by choosing Edit > Edit mode) you’ll be able to click around your patch window.
Inlets and outlets
Almost everything we use in Pure Data has inlets and/or outlets. To connect to ‘lets, we click and drag from any in to any out, or vice versa. This is what we will call “wiring”.
Our first path
We’ll start with something fairly basic. Don’t be scared. I’ll explain everything.
This might look like a jumble of random objects, but is, in fact, a very simple oscillator. From the top, shall we?
The osc~ object
The osc~ generates an oscillating cosine wave. The signal is sent out from it’s bottom left outlet. In this case, it is connected to the top right inlet of the *~. In our example, osc~ is being used to generate our tone. In this case, it is a 440 hertz tone (the A above middle C on a piano). The 440 after osc~ is called our “creation argument”. Most objects in Pure Data have the ability to accept creation arguments, thus, affecting their attributes at the time the object is created. Creation arguments are not always required, though. In most cases, a default value is decided for the object in question.
The dac~ object
To get audio out of Pure Data and into our sound device, we use a Digital-to-Analog Converter. In this case, Pure Data’s dac~. If you have your Audio Settings properly configured, dac~ will shove anything from it’s inlets to your speakers (or headphones, earbuds, etc.). In short, this is required if you want to get anything to make sound.
The *~ object (and the * object)
Pure Data’s operations are base almost entirely around mathematical functions. Multiply (*) and signal multiply (*~) (more on what exactly a signal is later) are two such functions that allow us to multiply two (or more) numbers or audio signals. In this example, the signal multiply is being used to add two signals together. The first signal is the osc~ and the second is a volume control of sorts. Multiplying the two together controls the overall volume of the osc~. More on this later.
The vertical slider
There exists a number of types of controls that can be used to modify parameters and events used by Pure Data. One of those is the vertical slider. In this case, we are using it to control the amplitude (volume) of the osc~. The vertical slider has one inlet and one outlet.
The message
Like the vertical slider, the message exists to help modify and control parameters and events in Pure Data. I am using two messages here to help control the audio flow. Messages can be clicked with the mouse (when the patch is not in edit mode, Control-E on Windows and Linux, Command-E on Mac) to trigger events. The first message tells Pure Data to turn on it’s DSP (Digital Signal Processing) functionality. The second message… you guessed it, turns off it’s DSP functionality. In essence, this makes it easy for me to turn on and off the audio (instead of checking and unchecking the “compute audio” checkbox in the main window.
The signal
Notice how most of our objects end with a tilde? ~ This is to denote that the object in question generates an audio signal. Some objects (such as the multiply object) have control-generating and signal-generating flavors. You can also tell if an object generates a signal or a control by the style of inlets and outlets it has.
Inlets and outlets that have no fill are controls.
Inlets and outlets that have a dark fill are signals.
Putting it all together
- When we click on the ; pd dsp 1 message, audio is started and we can start moving the vertical slider up and down. Floating-point values between 0 and 127 (you can change this by right-clicking the slider and choosing properties, then change bottom and top under output-range) are generated by the slider and …
- …multiplied by 0.01 to make the effect volume range of the oscillator 0 to 1.27 decibels which is…
- …multiplied by a 440 cycles-per-second cosine wave generated by the osc~ which…
- …outputs to our Digital-to-Analog Converter which…
- …plays a 440 hz tone on our speakers at the volume chosen on the vertical slider until we…
- …click the ; pd dsp 0 message to stop all audio flow.
Conclusion
Hopefully, this short article gives you a bit of insight into just how simply Pure Data operates. Next time, we’ll take a look at creating some real music with Pure Data.
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