195 IST Student Guide for Laboratory Session - 6
Computer Peripherals - Audio
IST 195 Lab Using computer peripherals
The purpose of this lab is to understand how computer peripherals work. Here you will learn how
computers distinguish between analog and digital signals as well as how the computer acts as a
transducer by converting incoming analog signals to one of the standard format digital signals. In
this lab exercise we will be experimenting with audio signals using headphones but the principles
are the same for digitizing analog signals for other computer peripherals like keyboards, monitors,
mice, joysticks and printers.
Learning Outcomes
After completing this lab, you will be able to:
Describe computer peripherals and how they work
Explain the difference between analog and digital signals
Explain the concept of transduction
Use a digital audio editor called Audacity to create an audio clip
BASIC LAB B Level Lab
Part 1: Preparing to create an audio file
For this lab, you will create a short audio file using a standard recording format called .wav. Your
audio file should include the following components:
A timing track called a tick track
A personal audio/voice track
A music background loop
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IST 195 Student Guide for Laboratory Session - 6
Computer Peripherals - Audio
Part 2: Plugging in your headsets
The sound card is the hardware whose function it is to input and output audio signals for the
computer. The computers in the iLab have an integrated sound card, which means that the sound
card components are on the motherboard, rather than on a separate card. The input and output
connectors for the sound card are typically on the back of the tower, and are labeled and colorcoded. Refer to the diagram below for the function of each connection. (For the computers in the
iLab, you can find the input and output connectors on the front.)
a.
Connect the microphone to the pink microphone connector on the back of the
machine.
b.
Connect the headset to the green line-out connector on the back of the machine.
There are many tools for capturing and editing audio. We will be using an open source
application called AUDACITY. Audacity is a software application that allows you to record and
edit your sounds or audio. It is available at http://audacity.sourceforge.net. If you are doing this
lab at home, you will need to download and install a copy of Audacity. You might also have to
download a copy of the LAME Encoder, needed by Audacity to encode to mp3
format: http://www.free-codecs.com/Lame_Encoder_download.htm (if this site is down,
Google "lame encoder and you'll find a site that carries it.) It is a zip file, and you'll have to
unzip it before using the required .dll file.
CREATING A FOLDER ON THE DESKTOP FOR YOUR PROJECT
Create a folder in which to store your lab project on the desktop and later drag it into My
Documents. To do this, go to the desktop. Right click on the mouse. Select New Folder. A
folder icon will appear on your desktop. Name the folder IST195Lab6AudioProject or something
similar.
Part 3: Working with Audacity
1. Start Audacity
From your Start Menu Select All Programs Audacity. You should see a screen that looks like
this:
2. Generating a Click Track
a. To begin using Audacity, the first thing you should to do is create a click track. When musicians
record a song, they often begin by recording a click track. This track is used to set the timing for the
recorded music tracks. In Audacity, a click track is created as a stream of sound on its own track. In
the main toolbar, click Generate, and then choose Click Track.
b. You will see a dialog box that will allow you to determine tempo (beats per minute) of the audio
clip, number of beats per measure (bar) and the number of measures (bars) in you audio file,
amongst many other selections. For the purpose of this lab, you will only be using the tempo, beats
per measure and number of measures. You can experiment with tempo and beats per measure to get
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IST 195 Student Guide for Laboratory Session - 6
Computer Peripherals - Audio
a sense for how they affect your song. Change the number of measures to 8 so that you create a
smaller file.
c. After clicking OK, you will see a track filled with little waveforms.
d. You can now play your click track by pressing the green play button. While playing, you can
stop, pause, rewind, or fast forward at any time. Name the track MyTrack by clicking on Audio
Track and selecting Name. This will allow you to name your audio track.
e. Save your work. Press the stop button and save your Audacity project in the folder you created
earlier on the desktop, by clicking File Save Project As. Name your project
IST195Lab6Mix[netID]. Audacity will automatically create an .aup file by that name to contain
the audio data and track information that you create.
3. Adding your voice
a. With the help of the microphone of your headset you can create a .wav file of your voice. You can
narrate anything you like a rap, hip hop, poem, song lyrics, news story from the D.O but you
must begin by saying your name or you will not receive credit. Make sure your microphone is
plugged in. Check to make sure that signal is reaching the Audacity program by pulling down the
Input Level Meter (microphone icon). Select Start Monitoring.
b. You will see microphone as the input device on the Mixer Toolbar.
Troubleshooting note: If nothing appears as an input source, go to the View menu. Select Mixer
Toolbar. This will float the Mixer Toolbar above the Audacity window and should reveal the
available input sources.
You may want to MUTE the click track by clicking on the MUTE button on the left side of the
track. (This will prevent you from hearing it while you record your voice.)
c. To record your voice narration, click on the record button on the Control Toolbar. Begin speaking
or singing into your microphone. Set the audio level by sliding the microphone volume button left
or right. But you must begin by saying your name or you will not receive credit. Speak for 15 at
least seconds. When you are done recording, click on the stop button and name the track
Voice by clicking on Audio Track and selecting Name. This will allow you to name your audio
track. Now turn the MUTE button off, on the upper click track (by un-MUTING it.)
4. Play back your voice.
a. To play back your voice narration, click on the play button on the Control Toolbar.
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IST 195 Student Guide for Laboratory Session - 6
Computer Peripherals - Audio
b. Saving your work. To save your voice narration as a .wav file, select Export and select WAV
from the file menu. Save the file you created in the folder you created earlier on as
IST195Lab6Voice[netID]. Note: Youll be asked to enter in Metadata for the WAV file. If youd
like to add this information feel free, but this is not required, nor will it be graded, for this lab. To
move past this screen, click ok.
c. Check to make sure that your voice narration is in the file. To do this, double click the file and
you should hear it play back in Windows Media Player.
NOTE: This is the minimum that you will have to use Audacity for to earn a B-level grade in
this lab. If you do not plan to go further, please submit the WAV file of your voice narration
to the LMS assignment drop box. You may wish to check and make sure that your voice
narration is in the file. To do this, double click the file and you should hear it play in
Windows Media Player.
ADVANCE LAB A Level Lab
In order to earn an A-level grade, you will be required to add background audio to your
narration. This can be done using the voice narration project that you created. There is no
need to create an additional project.
5. Getting free audio loops
From Internet Explorer Window go to http://www.looperman.com/loops.php
You will see a screen that looks like this:
This is a free site but it requires a registration. It does not request any sensitive data and asks for just
an email address. The site will send you a password to your mailbox.
Loops are special chunks of audio data that have been set up in such a way as they can be played
over and over again and the beat will sound smooth and natural. Choose any type of loop you like
by clicking on the appropriate link. For the example, below, I have chosen a guitar loop.
6. Choose a Loop
Choose a loop and download the loop file. Put the file in the folder you created earlier for the
project.
7. Import the Loop into Audacity
Now, import the .wav file into Audacity. From the toolbar click the File menu, and then click
Import Audio. Choose the .wav file that you saved on the desktop. Audacity will place the
new audio into one (mono) or two (stereo) new tracks in your project.
You will notice that your imported audio does not cover very much time. Most loops are only one or
two measures long (typically four or eight beats). You should duplicate your loop by cutting and
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Computer Peripherals - Audio
pasting it. Click anywhere in the track or tracks containing the loop and use the following sequence
of keystrokes:
a)
b)
c)
d)
e)
f)
g)
h)
i)
j)
k)
Home to position the cursor at the beginning of the track(s)
Alt-E to open the Edit menu
Arrow keys to choose Select
Right arrow to open the submenu
Arrow keys to choose Cursor to End
Ctrl-C to copy audio into the Copy/Paste buffer
Alt-E to reopen the Edit menu
Arrow keys to choose Move Cursor
Right arrow to open the submenu
Arrow keys to select To Track End
Ctrl-V to paste the copied audio on the end of the track
You can repeat the last two steps (j and k) as many times as you want to add more copies of the loop
to the track(s). When you are finished, if you rewind and play, the loops should sound seamless,
with no clicks between them and smooth, even beats.
It should look something like this:
8. Playback your new audio clip
If you listen carefully to the loop and the click track together, you will probably hear that they are
out of synch with each other. If you paid careful attention when you were importing the loop, you
may have noticed that the tempo was mentioned in the file name. For instance, my imported audio
file was called: distorted_electric_guitar_riff_c_96bpm.wav. Toward the end of the name you will
notice 96BPM which stands for 96 beats per minute. Unless you changed the default settings on
your click track, it was recorded at 120 BPM. So your last task is to adjust the tempo of the
imported audio track to match the click track.
9. Synchronize Tracks
To adjust the tempo of your recorded tracks, begin by doing the first five steps under the section 7
above. This will select the whole looped audio track. Then click the Effect menu and choose
Change Tempo. In the dialog box you can enter the old tempo (96 BPM for my example), and the
new tempo (120 BPM to match the click track I recorded). Then click OK. The program will
compress the playback time of your selected loops so that the beats match the click track. Note: If
you can figure out the calculation, thats awesome, but you dont have to. By entering in the old
and new tempo, the program will figure this % change for you.
10. Saving your work
To save your voice narration and looped audio as a .wav file, select Export, from the File menu,
and save as WAV. Save the file into the earlier folder that you created and name it as
IST195Lab6Mix[netID]. Upload the WAV file only to the LMS assignment drop box to obtain full
credit.
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IST 195 Student Guide for Laboratory Session - 6
Computer Peripherals - Audio
For B level credit, the file in your LMS assignment drop box should have all of the following
elements:
A .wav file submitted to the LMS assignment drop box (generally about 16 seconds long, if
you record 8 measures of click track, about 2.69 MB) that contains:
o a click track, generally 120 BPM, 4 beats per measure, 8 measures
o your voice narration at the beginning
For A level credit, the file in your LMS assignment drop box should have all of the above
elements, including:
Looped audio (e.g. drums) in which the beats match the click track
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