Homework: Radio Play

  • Out: Nov 1, 2022 Tuesday
  • Due: Nov 15, 2022 Tuesday


Compose a short musical radio play (1~2 min.) consisting of sounds spatialized binaurally.


  1. Record: Record monophonic audio files and trim them with an audio editor. Use your DIY air mic if appropriate.
  2. Play: Use Chuck's SndBuf (mono) or SndBuf2 (stereo) UGens to read in and play .wav files after preloading them in JavaScript. This example plays a whale clip.
  3. Spatialize: Use Ambisonic Spatializer to spatialize monophonic audio files in stereo binaural and save the results. Use headphones or earbuds.
  4. Automatic Mix: Compose the stereo files into a final mix using a webchuck script which will position the spatialized files in time with respect to each other. Example programmed sequence of clips (demonstrating different spatializations).
  5. Save: Save the final webchuck mix using the record feature and name it hw4.wav -- this single stereo .wav file will have binaural content so it'll need headphones or earbuds for listening.
  6. Post: Copy the final file to your top-level homework factory directory. It should be there as 220a/hw4.wav (and not in a subdirectory).


Binaural recording uses stereo mics pointed outwards from inside your ears to capture as closely as possible the exact sound pressure waves entering your ear canals. Headphones (or ear buds) need to be used to listen to binaural stereo. An early binaural radio play produced by the BBC, The Revenge demonstrates the possibilities. Use headphones or earbuds to listen to it! The binaural technique captures filter (transfer function) differences of sounds arriving from various directions, differences which are caused by body parts shadowing and reflecting the sound: ear flaps (pinnae), head, shoulders, etc. Played back over headphones or earbuds, binaural preserves the interaural loudness difference (ILD) and interaural time difference (ITD) cues which are basic to sound localization.

Early work in binaural recording was accompanied by predictions that its superior imaging would create a world where everyone would eventually listen through headphones. Playing binaurally-encoded sounds over stereo loudspeakers doesn't result in either good binaural or good stereo and that's probably held back wider use. For a position paper, see Jens Blauert's AES Heyser Lecture. He makes a provocative case for binaural as a part of an increasingly realistic synthetic world.

Janet Cardiff and George Bures Miller are a pair of artists whose work leverages the medium. They compose site-specific 3D audio narratives with spine-tingling interplay of real and phantom presences, binaurally-produced. A stunning work, Alter Bahnhof Video Walk (- select the video page - use headphones or earbuds), opens up possibilities of what you might compose for mobile devices. Like Cardiff's earlier sound walk, The Telephone Call, at SFMOMA (2001) the piece leads its participants on a physical journey, each directed by a mobile device which they are holding while watching a pre-recorded self-guided tour. You'd turn a corner and someone would be there musicking in some way in the space (convincingly, so you could point to them) only they weren't there then, but at some other point in time, past, alternative present, or future.

Ambisonic Spatializer was developed for 220a by Hongchan Choi and uses elements of the Resonance Audio project. .



You can make this a purely literal radio play with the constituent tracks comprising dialogue and sound effect elements of a play (for example, closing doors).

  • A drama using your own voice for all parts or enlisting some friends to play some parts.
  • A recitation or speech.

However, you could also tilt it more toward music:

  • A conversation between Peter Pan and Tinkerbell, where Tinkerbell is a sound/melody you play or synthesize - Tinkerbell flies around in the sound space.
  • Simulating a rehearsal, where a director / conductor approaches the center of the stage from one side, and then rehearses with some musicians positioned on different sides of the stage.

Tracks, stems, clips: what's in a nane?

  • Some ambiguity here but we'll stick with these ideas.
    • audio editors often refer to tracks
    • mixes consist of edited tracks often called stems
    • clips are video clips, sound clips -- some chunk of media, a recorded clip, a finished clip

Key Steps

  1. The assignment work starts with recording monophonic sound sources (as monaural audio files) and spatializing them.

    • Equip yourself with a digital audio editor, for example, the audacity application or audiomass which runs in the browser or an editor of your own choice.
    • Learn to
      • record from your audio interface and microphone
      • load .wav files from your local file system
      • save your work as a .wav file (in mono or stereo) at 48kHz sample rate
        • (note: audiomass editor was limited to 44100 Hz but a fix for 48kHz is underway)
      • edit segments with select, time move, cut, copy, paste
      • mix multiple tracks
      • apply effects to a track, for example, reverb or filter
    • Practice recording and playback using your audio interface, mic and headphones (not the computer's built-in mic and speakers). Make sure the analog input gain and output volume levels are well-adjusted to avoid noise or clipping.
    • Record and export 4 different monaural files into the same local directory on your local computer (come up with a simple naming scheme, like "stem1.wav", "stem2.wav", ...).
    • Re-record the tracks adding spatial movement using the Ambisonic Spatializer. Use headphones or earbuds.
    • Open your stems directory with "Choose Files" and multiple select 4 files -- test "Play / Pause" with the four buttons at the bottom -- practice moving sounds around one at a time with the mouse -- and, for example, select "Room Size" = "Huge" and select "Wall Material" = "Marble" -- reload the page if you want to start from scratch.
    • For the assigment, choose the acoustical space you need -- first click "Record", then click the sound's "Play" button and start moving it -- when done, click the sound's "Stop" button, Right-click on the save text and then "Save Link As" -- check that there's a new binaural stereo file where you intended. Load it into your audio editor and check that it plays there ok.
  2. Put the stems on the server. Our one-click, run anywhere, .html web pages get them from there.

  • use the scp method to copy the directory from you own local machine to the server (put it right under 220a and not in a subdirectory)
scp -r MY_STEMS_DIRECTORY USERNAME@ccrma-gate.stanford.edu:Library/Web/220a/

The above command requires replacing MY_STEMS_DIRECTORY with your local stems directory name and specifying your CCRMA USERNAME (if your username is the same locally then you can elide USERNAME@

Allow ubiquitous access.

  • add a hidden file to it called .htaccess which sets the permissions for web access (that is dot htaccess)
ssh USERNAME@ccrma-gate.stanford.edu
cd Library/Web/220a/MY_STEMS_DIRECTORY
cp /usr/ccrma/web/html/courses/220a/examples/webchuck/radio-play/wav/.htaccess .
ls -als

This time you are logging in remotely to your CCRMA directory and changing to your new stems directory. The hidden file for access has that really long pathame (where you pick it up from the course directory) and you copy it to your new stems directory. Hidden files have names that start with a dot. Reference to "this directory" is also with a dot. The cp command just makes a copy of the intended file to the right place. The last ls -als command lists the files including revealing any hidden ones. You should see your stems plus the .htaccess file.

Chuck Mix Script for Automated Temporal Layout and Layering

The radio play should have a total duration of a couple minutes or so. The Chuck portion of the project will do the final assembly. Create a Chuck script that will read in your spatialized files and combine them into one output mix. The same example as above serves as a model of how to program a sequence of clips. Save your final webchuck mix using the record feature and name it hw4.wav -- this single stereo .wav file will have binaural content so it'll need headphones or earbuds for listening. Copy the final file to your top-level homework factory directory. It should be there as 220a/hw4.wav (and not in a subdirectory).

Scripting the mix this way adds possibilities of combining elements we've seen in previous assignments. Sounds and sound effects added to the mix script might employ, for example, data sonification, illusions, effects or patterns. Here's an example combining a sound file with a tone repeating faster and faster.