The Research Experience for Teachers Program http://www.cs.appstate.edu/ret

Title: Song writing with power functions

IntroductionThis lab utilizes Audacity’s editing functions to use a single recorded sound to create

entire scales of music that can be used to synthesize any song.

Audacity is a basic digital recording program that can record, edit and playback audio. It employs a Graphical User Interface (GUI) for manipulating audio files encoded in “regions” that can be altered and rendered into many commonly used audio formats.

Materials List:

Capable computers with Audacity Built-in microphone, USB microphone or a traditional microphone with A/D

Converter

Procedure:

Background:

You should have some experience with power functions and their graphs. You will work in teams to record and process audio with Audacity.

Preparation:

You need to make sure that Audacity is installed and working on your computer.

Lab Activity:

Step 1 - Recording and Importing Audio

In Figure 1 you can see Audacity’s home screen divided into several sections. The main part, in the center, is where sound waveforms can be found. If no audio has been imported or recorded, this section will be gray. Along the top, from left to right, are the recording controls, editing tools, output volume, input volume and editing controls. Below them are the sound card, output, microphone and audio channel choices. The strip of numbers along the top of the waveform window is the time index. At the bottom, from left to right, are the project sample rates and transport windows.

To record a new piece of audio you can use the microphone built into the computer or connect a microphone of your own and select it in the microphone selection menu. Once the microphone is connected, all you have to do is hit the record button and a new track is automatically created and continues to record until you press stop. To import an existing

audio file, use the file menu at the top of your window and select import. Then choose your desired audio file. To hear the audio simply hit the rewind button and push play.

Figure 1 – Audacity’s Home Screen

Step 2 – Editing Audio

You can use many common editing functions that exist in programs like Microsoft Word such as cut, copy, paste and delete. To do this, choose the selection tool, highlight a section of audio and use the edit window or key commands to execute the function. Try copying a piece of audio and pasting it onto a different audio track. You can add audio tracks by selecting the “Tracks” menu at the top of the window and add new. Put your new waveform on the new track by putting your cursor on it and pressing paste. The new waveform region should appear. Highlight the new region and select the effects menu. Here you can edit the pitch, length, amplify or add effects to your new audio.

Step 3 – Analyzing Audio

Open a new file and record a one to two second clip of audio that can be your own voice, a noise or any random sound you would like to record. Highlight the audio, select the Analyze Menu and choose Plot Spectrum. In Figure 2, you can see many statistics of your selected audio. One of the most useful features of the spectrum graph is that you can see the approximate frequency (musical note) of your audio. What note was the audio you selected? What was the frequency?

Figure 2 – Plot Spectrum analysis

Step 4 – Altering Audio Pitch

To change the pitch of an audio region, highlight the section of audio you wish to alter. Select the Effect Menu and choose Change Pitch. A window will open up, Figure 3, giving the current frequency/note and allow you to choose if you want to raise or lower the pitch. You can also choose what note you would like to change it to or enter it manually. When you have selected your desired pitch shift, hit OK.

Figure 3 – Change Pitch window

You can change the note manually using the following power function algorithm:

ND =NC(1.059)X

Where ND = Desired Note

NC = Current Note

X = Number of musical half-steps from

current to desired note.

Use these processes to take your recording and make a full octave of musical notes based on your original audio region. Can you take your twelve notes and recreate a popular song?

Figure 4 – A song written with a single audio recording.

Assessment

Pre-Assessment

Students should predict relationships for the following concepts before the lab:

1. How can power functions model real world situations?2. Can you evaluate and graph power functions?3. How do rates of change of linear and power functions differ?

Results/Conclusions

1. How did changing the frequency change the pitch of the sound?2. How did changing the frequency change the length of the audio region?3. How did the algorithm relate to the change in frequency?

Reference(s):

Appalachian State University RET Program 2013.