play_solns

Buffer¶

Buffer is a UGen to store data on the audio server. For our purposes, we will use Buffer to store audio data. An audio file is simply a sequence of numbers called samples. For SuperCollider, use audio file formats like .aiff and .wav (i.e., uncompressed and lossless files). Audio files generally contain one or two channels of audio data called mono or stereo. If you want to use an audio file in SuperCollider, you need to know ahead of time whether that audio file is mono or stereo.

Step 1: Find the path to an audio file to play¶

In order to play an audio file, you first need to know where the audio file exists on your computer. Every file and folder on your computer has a path associated with it. If you are running this code within the SuperCollider IDE you can use the shorthand below. thisProcess.nowExecutingPath gives you the file path of the current .scd file you are working with. .dirname gives you the folder where your file is located and then the operator +/+ joins the path of the folder with the sounds folder that resides in that folder.

If you are running this in the notebook, then you need to compute this manually. First find the folder that has the notebook and then get the path to the sounds folder.

If on a mac: https://setapp.com/how-to/how-to-find-the-path-of-a-file-in-mac
If on a PC: https://www.howtogeek.com/670447/how-to-copy-the-full-path-of-a-file-on-windows-10/

Note in the SuperCollider IDE, you can also just drag the file or folder onto the screen and the path will be rendered automatically.

Run this if in the SuperCollider IDE¶

Set this variable for the sounds folder if in the notebook¶

In [2]:

~buffer_folder_path = "/Users/andrewdavis/Documents/CS/Wellesley/CS203/lecture_materials/play/code/sounds" // enter your path here

If the above worked then let's playback some sounds.

Step 2: Creating a Buffer¶

The sounds folder associated with this lecture has three audio files in it: poker.wav, hello.wav, and guitar.aiff. Let's create a buffer to store each one of those audio files.

Using PlayBuf to play a buffer¶

The UGen PlayBuf is the convenient way to play an audio buffer on the server. PlayBuf needs to know ahead of time the number of channels the audio file has. Therefore, there are two versions of a SynthDef designed to play an audio buffer: a mono and stereo version. The first argument to PlayBuf is the number of channels. Notice how mono_play uses 1 and stereo_play uses 2.

PlayBuf also takes a buffer object to read from and then several additional arguments. Of particular interest are the arguments rate which affects the speed of playback and loop which can loop the audio file indefinitely. PlayBuf also accepts a done action as its last argument. We can set the done action to 2 to free the synth automatically when the audio file has finished playing.

In [6]:

SynthDef(\mono_play, {
  arg outBus = 0, buf, rate = 1, loop = 0, amp = 1;
  var sig = PlayBuf.ar(1, buf, rate: rate, loop: loop, doneAction: 2);
  
  sig = sig ! 2; // convert mono sound to stereo array to hear out of both speakers
  Out.ar(outBus, sig * amp);
}).add;

Stereo version of the SynthDef above.

In [9]:

SynthDef(\stereo_play, {
  arg outBus = 0, buf, rate = 1, loop = 0, amp = 1;
  var sig = PlayBuf.ar(2, buf, rate: rate, loop: loop, doneAction: 2); 
  Out.ar(outBus, sig * amp);
}).add;

Changing the rate of playback¶

The playback rate can be changed using the play argument in PlayBuf. This is a crude way to change the pitch of an audio file or computer-generated sound like a sawtooth wave. Essentially audio samples are skipped or added to account for the respective contraction/elongation of the playback. We'll learn more about why the pitch drops or rises when we talk about digital representation.

Increasing the playback rate raises the pitch and shortens the duration of the audio file. The file sounds more like a chipmunk now.

Decreasing the playback rate drops the pitch and extends the duration of the audio file.

You can also playback the audio file in reverse as well if you provide a negative rate. Note here that I have also looped the file as well.

In [38]:

~hello_synth = Synth(\stereo_play, [\buf, ~hello_buf, \rate, -1, \loop, 1]) // halving the playback rate

Adding Effects to Audio¶

One of the interesting ways to use audio files in SuperCollider is to route the output to an audio effect. Below we will create a SynthDef that creates a reverb effect giving the sound more space.

In [40]:

SynthDef(\reverb, {
  arg outBus = 0, inBus, mix = 0.5;
  var sig;
  
  sig = In.ar(inBus, 2);
  sig = FreeVerb2.ar(sig[0], sig[1], mix: mix);
  Out.ar(outBus, sig);
}).add;

Open up a plot tree to see the nodes on the server.

Create the reverb synth and a bus to connect to it.

Execute the cell below to play the guitar track through the reverb. You can change the mix of the reverb to increase/decrease the amount of reverberated sound. Because the SynthDef \mono_play uses a done action of 2, the synth will free itself automatically once it is done playing.

Play¶