Physics of Music PHY103 Lab Manual 2011Lab 2 – Periodic Signals – Triangle and Square WavesEQUIPMENT and PREPARATIONINTRODUCTIONPROCEDUREFinishDATA ANALYSISQUESTIONS and DISCUSSIONPhysics of Music PHY103 Lab Manual 2011Lab 2 – Periodic Signals – Triangle and SquareWavesEQUIPMENT and PREPARATION- Computers- Know how to screen snap so that images can be sent home by students.- Headphones - Microphones + Preamps + cables and associated connectors, adaptors and cables. It should be possibleto record sound into the computer using Adobe/Audition. Do a record sound check on all computers!- Microphone stands- Musical instruments and/or sound-making devices- Pasco open speakers- Oscilloscopes, and way to connect speaker to oscilloscope (BNC to banana adapter + banana plug cables)Warning: do not place speakers near oscilloscope screens as they can damage the CRT screen.INTRODUCTIONIn this lab we explore the gap between electronics and music by generating and observing signalswhile listening to them. We will explore the relation between the shape (waveform) of a sound, itsspectrum and the timbre or character of the sound. We will have the chance to create some sounds of ourown and record them onto the computer. The computer software lets us look at sound waves as a signal asa function of time (waveform view) and as in terms of their frequency distribution (frequency or spectralview). To do compute the spectrum we will use the algorithm known as the Fast Fourier Transformation(FFT). The FFT is an efficient computational algorithm that breaks down a signal into a number of basicsine waves of specific frequencies. In this lab we will become familiar with the Adobe-Audition audio software. Triangle, square and sine waves are all periodic signals. In this lab we will find that periodicsignals have frequency spectra with particular properties (integer harmonics). We can record our voice andmusic instruments and will find that the spectra of these sounds have similar properties to the periodicsignals generated by a function generator.PROCEDUREPart I – Setup1. Make sure the computers are on.2. If there is a lot of noise in the room, you can use headphones by unplugging the speakers andconnecting the headphones into the speaker jack. If you are using speakers connected to thecomputer, make sure they are turned on (turn the knob on one of the small speakers).3. Make sure that your microphone is connected to the preamp and that the preamp is plugged in. Thegreen power indicator should light up. The +48V button should be pushed in. This is to powerthe microphone that employs a capacitor. The capacitor creates an electric field between twoplates. The plates respond to small pressure variations (such as those made by sound waves)creating a signal that is amplified by the preamp and passed on to the computer where it isconverted into digital format. Powered microphones are usually superior to un-powered ones.4. Make sure that the preamp is connected to the computer through the preamp’s output jack and thecomputer’s input microphone jack.Physics of Music PHY103 Lab Manual 20115. Run the application Audition on the computer by double clicking the AU icon.Part II – Looking and Listening (triangle, square and sine waves)In this part of the lab you will generate tones using Adobe-Audition, you will view their waveforms and listen to their sound.1. Click the generate menu and choose TONES. The first time you do this a window titled “NewWaveform” will come up. Set the sample rate at least at 48000Hz. Set the Channel to “MONO”.Set the Resolution to at least 16 bit. Then click OK.2. In the box labeled “Presets” choose a A440 default. 3. On the bottom right, set the duration to 1.0 seconds. 4. Just above that, in the box labeled “General”, chose a “flavor” of “Sine”. The flavor is the type ofwaveform created. You can listen to this by clicking “Preview”. Click OK Now you have awave.5. Click on the wave you have created and hit the key on your keyboard labeled “END”. This willsend the cursor to the end of your sound file. You will now create two mores sounds with thesame pitch.6. Repeat step #4 with a flavor of “Triangle/Sawtooth”. Repeat step #5.7. Repeat step #4 with a flavor of “Square”. Hit the “Home” key on your keyboard to place yourcursor at the beginning of the file. 8. You now have 3 one second waves. Click on the green right arrow key (bottom left) to play thesounds. You can adjust the volume with the volume icon on the computer on the lower right orwith the knob on one of the speakers.9. Describe in your notebook your perception of these sounds.10. Looking at the waveforms. Left click on the waveform somewhere. Use the magnifying glassbutton (top row, on bottom of screen, circle with a + sign in it) to expand the x-axis. Take a closerlook at the waveforms. You can play the sounds again while watching the waveforms move byhitting “Home” and then play. You can click and drag the green bar above the waveform to viewdifferent parts of the wave. You can also expand the horizontal axis by right clicking anddragging. To zoom out: right click on the axis and choose “Zoom full.” The button with a circleand a – sign will also allow you to zoom out.11. Draw in your notebook, the shape of the waveforms (including labeling the x and y-axes) or sendyourself a snapped view.Figure 1. Above is a spectrum of a flute playing note A#5. Each peak is an overtone (partial or harmonic). The vertical scale is in dB, or 20log10 (amplitude) or 10log10(power). You can measure the strengths of the overtones from the strengths of each peak. The fundamental is at about 932 Hz, the first harmonic is at about twice this at 1900Hz and is weaker than the fundamental. Notice that 1900Hz is about twice as big as 930Hz. The note played is A#5 (the A# in the octave above middle C) but actually the lower octave A# is also weakly excited and you see some A#4 in the spectrum corresponding to peaks at 466 and 1400Hz.Physics of Music PHY103 Lab Manual 2011You can adjust the x-axis of the spectral window to make a better measurement of the frequencies of the peaks. The y-axis here is in dB which means decibels. This is a logarithmic scale (note the negative numbers!). A small change in dB represents a pretty big change in power. A change of 10 dB is a factor of 10 in