Tuesday, December 2, 2014

Exercise 8

Reading:

Please read chapter 7 from Miller's book.

Problem Set:

  1. A sinusoidal plane wave at 40 Hz. has an SPL of 80 decibels. 
    1. How far does the air move? (I.e., what is its RMS displacement?)
    2. What is the change in SPL (in dB) if the wave maintains this RMS displacement, but the frequency changes to 80 Hz?
  2. A rectangular vibrating surface one foot long is vibrating at 1000 Hz. Assuming the speed of sound is 1000 feet per second, at what angle off axis should the beam's amplitude drop to zero?
  3. How many dB less does a cardioid microphone pick up from an incoming sound 90 degrees (pi/2 radians) off-axis, compared to a signal coming in frontally (at the angle of highest gain)?
  4. Suppose a sound's SPL is 0 dB. What is the total power that you ear receives? (Assume that the opening is 1 square centimeter).
Home Lab:

Work on your final projects! Remember, they're due next week!

Tuesday, November 18, 2014

Exercise 7


Reading: 

Please read chapter 6 from Miller's book.


Exercises:

For these exercises, assume the speed of sound is 343 m/s, and the air density is 1.225 kg / m^3 .

1) A car is moving toward you at 83.71 miles per hour. Its horn is blowing at 440 Hz. By how many half-tones does the sound rise above 440 Hz because of the car's motion?

2) Suppose the same car has the same horn blowing, but now you hear a pitch of 405.64 Hz. Assuming the car is moving directly away from you, how fast is it moving (in miles per hour)?

3) A sound has a wavelength of 5.7167 meters. What is its frequency?

4) If two sounds are a perfect fifth apart, what is the ratio of their wavelengths?

5) Suppose that 2 furlongs away from a loudspeaker the SPL is 60 dB. The speaker is the only object making sound nearby, and is a point source. What is the SPL 4 furlongs away from the loudspeaker? 1 furlong = 201.168 meters.

6) A 171.50 Hz. sinusoid is traveling in a plane wave in the +x direction. Two microphones are placed at x = 0 and x = 1 meter, respectively. What is the phase difference, in radians, between the signals picked up by the two microphones? 


Home Lab: 
This project shows how to measure the frequency response of a filter, whether it's a designed one (as in this case) or it's something that acts as an unintentional filter (such as a loudspeaker that doesn't have a flat frequency response--and, in fact, none of them do.)
The filter we'll measure is the bandpass filter supplied in the music 170 library (called ``bandpass"). It's a classical filter design that appears often in digital audio applications.
To measure it, make a ``sinusoid" object and pass it through a ``bandpass" object. Make two ``meter" objects, and connect one to the output of the oscillator (so that you see what you're inputting to the filter) and one to the filter output so you can see how the two levels differ.
If you want to save time later, you can slightly complicate the patch by inserting a multiplier between the oscillator and its two connections (with a constant to multiply it by) so that you can adjust the oscillator's output to a round number in dB; but this isn't necessary to finish the project.
We're interested in two settings of the filter: the center frequency should be 1000 Hz, and the value of ``Q" set to 10 and to 20. For each of these two filter settings do the following:
Set the oscillator's frequency to a series of values separated from 1000 by half octaves:
31, 44, 62, 88, 125, 176, 250, 353, 500, 707, 1000, 1414, 2000, 2828, 4000, 5656, 8000
 
With these numbers evenly spaced on the horizontal axis (a logarithmic scale), plot on the vertical axis the gain in decibels (the output level of the filter minus the input level). These numbers will all be negative. (Suggestion: find all the 34 values first--each filter's gain at each of the 17 frequencies shown--so that you will know what the bounds of the graph should be.) Draw two traces, one for each of the two filters. Enjoy the fact that at high frequencies you get two nearly parallel lines. How many decibels per octave do the filters' frequency responses drop off by at frequencies above about 2000?

Monday, November 17, 2014

Acoustics Animations by Dan Russell

Here are some wonderfully demonstrative animated gifs by Dan Russell, acoustics professor at Penn State:

http://www.acs.psu.edu/drussell/demos.html

I find these to be helpful when I'm trying to picture simple wave interactions. Hours of wavy entertainment!

For example, here's what breaking the sound barrier looks like:

Thursday, November 13, 2014

Exercise 6: Final Project Proposals

Due Tuesday, 11/18.

Please write a description of your proposed final project. Each team will submit a single document. The target length is 1 page, double spaced, 12 point times font, normal margins (no funny stuff).

Things to consider when writing this document:


  1. Summarize the core goals - What deliverables are you proposing to have completed by the deadline? 
  2. Explain your reasons - Why is this an interesting and relevant final project for the class? Why is it complex enough to be worth 1/3 of each of your grades?
  3. Explain your team's methods - How will you complete the project? Why is it a realistic undertaking given the timeline, budgetary considerations, and skill-set of your group? 
  4. Bonus - What specific roles will each team member perform for the completion of the project? 
  5. Bonus - What is your team's project timeline?
  6. Bonus - What is your team's budget? Where will you find materials?
The questions marked "Bonus" are largely there to get you thinking. Furthermore, answering all of these questions in a satisfying way will increase the likelihood of your project being accepted (and possibly your grade on the assignment).

We will give feedback on the project proposals. If your team's idea is not accepted or requires revisions, we will let you know. This will be handled on a case-by-case basis.

You and your team have probably been thinking about the final project a good deal by now. However, if you need to see the prompt again, please refer to the syllabus, linked here.

Sunday, November 9, 2014

DIY Resources

Here are some resources, both online and local, that might be helpful as you plan your projects.  There are plenty of avenues to explore here, so we caution you to be realistic in evaluating what you’ll have the time and ability to pull off.  Happy adventuring!

Electronics hobbyist stores:

www.sparkfun.com
www.adafruit.com


Electronics parts suppliers:

www.mouser.com
www.digikey.com
www.jameco.com


Hardware:
www.mcmaster.com


Local Hardware/Surplus/etc.
www.marshallshardware.com (in Miramar)
www.murphyjunk.net (El Cajon)
www.surplusdepot.org
www.we-supply.com


Embedded computing platforms:

www.arduino.cc
www.raspberrypi.org


Beginning synth DIY:

musicfromouterspace.com


Guitar FX DIY:

www.smallbearelec.com
www.generalguitargadgets.com


Random DIY:

makezine.com
www.instructables.com


Learn to solder in 1980:
www.youtube.com/playlist?list=PL926EC0F1F93C1837

Wednesday, November 5, 2014

Yaybahar by Görkem Şen

Someone brought this gentleman's novel musical instrument to my attention today. I thought I'd share it with you folks:

http://vimeo.com/110633932

He's using membranes to amplify the sound of the springs, rather than a pickup. The whole thing is acoustic. It sounds lovely!

Monday, November 3, 2014

Exercise 5

1) A stretched violin string has 50 N tension and 1x10^(-2) kg / m linear density. What is the propagation speed of a transverse wave traveling on this string?
2) Violin strings are typically 60 cm long.
a) What is the frequency in hertz of the first mode on the string?
b) How about the third?
3) Another string on the violin has the same length and tension, but its linear density is instead (4.44x10^(-3) kg / m).
a) What is the propagation speed of a transverse wave on this string?
b) When played together, what interval (in semitones) will separate the two strings?
4) What is the frequency of the second mode on the string from question 3?

Thursday, October 30, 2014

Just Intonation App / Compilation!

Thought you might be interested in a simple program I wrote (back in '09...) for calculating Just Intonation scales based on overtones. The link is here: http://www.joemariglio.com/winter09_10/scale_calc_browser/
In case you want the non-browser version: OSX WIN LNX
It offers a geometric way of constructing scales that line up with user-select-able equal divisions of the octave. Super basic, but possibly helpful?

KEYBOARD COMMANDS:
"+" - increase number of vertical bars (tones equal temperament)
"-" - reset number of vertical bars to 2
"c" - clear scale buffer
"r" - return scale buffer, printing to file named with date and time, located in app directory (file io won't work in browser version)

Another Just-Intonation related thing you might like is a compilation from the 80's, put together by a tape cassette 'zine' called Tellus, which was distributed out of a small arts collective in New York, called Harvestworks: http://www.ubu.com/sound/tellus_14.html .
This compilation features a multicultural take on Just Intonation, and even includes our friend Harry Partch!

Happy Tuning!

Tuesday, October 28, 2014

Exercise 4

Readings: Please read Chapter 4 from Miller's book.

Exercises:

1. In the Western tempered scale, if A is tuned to 440 Hz., what is the frequency of the D below it?

2. What is the frequency of the same D as in problem 1, using the Just Intoned scale in D instead of the tempered scale?

3. A major triad may be formed by the frequencies 100, 125, and 150 Hz. Another may be formed of frequencies two octaves up: 400, 500, 600. Which triad is likely to sound "sweeter"? Why?

4. How many equal-tempered tritones does it take to span the normal frequency range of the human ear?

5. Imagine a tuning system not based on equal divisions of an octave (R = 2), but rather a tripling of value (R=3). Assuming we keep the familiar 12 equal divisions of this "tritave", what would the equivalent of a major 3rd (ie, 4 "half-steps" up) be as a ratio?

Home Lab:

How much detuning makes an interval sound sour? This project is a test of the Helmholz theory of consonance and dissonance. The interval we'll work on is the fourth below 440 Hz. (and later, 220 Hz.)

First, using "sinusoid" objects, make a perfect fourth using the frequencies 440 and 330. You can connect them to the same "output" object so that they have the same amplitude as each other. Now drag the 330 Hz. tone down in frequency until, to your ears, the result starts to sound ``sour". How many Hz. did you have to decrease the 330-Hz. tone to make it sour? (If it never sounds sour to you at all, just report that.)

Now do the same things with pulse trains. You'll need the "pulse" object. Make two of them, frequencies 440 and 330, with "BW" (bandwidth) set to 2000, and connect them to an "output" object as you did with the sinusoids. Now reduce the 330-Hz. one to 329. What do you hear?

Now reduce it further until it sounds sour. How many Hz. less than 330 did you have to go? Was it further away than the tempered fourth (329.628)?

One could think that the number of Hz. you have to mis-tune an interval to get sourness might be a constant or else that it might be a constant proportion (i.e., interval). To find out, repeat the experiment for 220 Hz. and 165 Hz. Again, decrease the lower frequency (165) until you think it sounds sour. How many Hz. did it take and is it more nearly the same frequency difference or the same proportion?

Monday, October 20, 2014

Exercise 3

Readings:

Please read Chapter 3: Spectra from Miller Puckette's website.
Also, Chapter 2 from the Pierce book.

Exercises:

1) a) How many octaves above the fundamental is the 11th harmonic?
b) if the fundamental is 440 Hz, what is the frequency of this harmonic?
2) What is the closest equal temperament approximation to the interval between the 4th and 5th harmonic?
3) A low-pass filter has a frequency-dependent gain (as a ratio, not in dB) of
g(f) = 1/sqrt(1+(f/500Hz)) .
What is the gain, in dB, at 2000 Hz?
4) A virtuoso flautist, playing a perfect 1 kHz tone, generates only the first 3 odd harmonics with her instrument. At that very moment, a tugboat passes by and sounds its 55 Hz foghorn, containing the first 20 harmonics (even and odd).
a) What are the two harmonics closest in frequency to each other in this coincidence?
b) Are they within 10 Hz of each other?
c) Are they within a critical band?

Home Lab:

Critical bands and loudness. This project tries to investigate how loudnesses of clusters of sinusoids are perceived differently when they are spaced withing a critical band than otherwise. For this experiment you should try to set yourself up with a reasonable listening environment, either using headphones or playing through a stereo (but not your laptop speaker).

Start by connecting a single ``sinusoid" object with frequency 1000 Hz. to an ``switch" object (these objects are both in the Music 170 library).

Now make another version (in the same patch) with four sinusoids tuned to 960, 980, 1000, anad 1020 Hz.. Connect all four to th input of a second ``output" so that you can turn them on and off as a group, independently of the first one.

Make a third group of objects in the same way (or just duplicate the second group) but now set the frequencies to 500. 1000, 2000, and 4000.

Now, by turning them on and off (using the on/off control on the three output objects) equalize the outputs until all three are at a comfortable (reasonably soft) listening level. (If you have to push any of the output gains past about 90 dB, you should turn up your speaker instead. On my system I'm using gain values between 50 and 70.)

Now adjust the three output gains so that, as you turn them on one at a time, you judge them to have roughly equal loudnesses. Write down the three gain values you had to use to equalize them.

Since the four frequencies are roughly at the same level on the equal-loudness contour chart (Wikipedia is your friend), the different frequencies should be less a factor than the spacing. Is it in fact nearly true (or totally false) that in the close spacing example, you ended up adjusting the complex tone so that its power was roughly equal to the power of the single 1000 Hz. tone? Is that still true when the four frequencies are spread widely (500-4000)?

Tuesday, October 14, 2014

Exercise 2

1) Take a look at the sinusoid in Exercise 1, Problem 1. How many samples would you need to delay the recording by to make a sinusoid that is perfectly out of phase with the original?


2) Without adjusting either signals' level, mix the sinusoid from Exercise 1, Problem 1, with the sinusoid from Exercise 2, Problem 1. What is the estimated peak amplitude of the resulting signal?


3) 18th century Viennese pianos have 2 strings per note. Yours is fairly out of tune. You press a single key corresponding to strings with frequencies 440 Hz and 450 Hz. What is the frequency at which the resulting sound "beats"?


4) In a fit of indiscretion, you multiply a 15 kHz sinusoid by a 12 Khz sinusoid, recording it at a sample rate of 40 kHz. What two frequencies result?
Home Lab:


The homelab can be found here, after the numbered questions, under the heading "Project". Answer the questions related to this lab and include them with your responses to the Problem Set.

Saturday, October 11, 2014

Decibels in PureData

Just a quick reminder for those of you working on the Project for week 1:

PureData uses a slightly different form of dB than the one we derived in class. To convert between the two, simply add 100 to the level in standard dB to get the level in PureData's dB. Similarly, to convert a PureData dB to standard dB, subtract 100.

Professor Puckette could likely defend his decision for this better than I can, but I imagine he did this to keep the PureData dB values positive.

Tuesday, October 7, 2014

Exercise 1

Due Tuesday, 10/14, by 3:30pm.
Show your work!


Problem Set:



1. A recorded sinusoid has a sample rate of 48 kHz and a frequency of 660 Hz. What is its period in samples?
2. You take a recorded sinusoid of your favorite frequency, invert it, and multiply it by 2.
a) What is the change in gain?
b) How about the change in level (dB)?
3. What frequency is 1/2 octave above 330 Hz.?
4. A Nintendo Gameboy has 4 Digital-to-Analog Converter (DAC) channels, each capable of producing sound with a word length of 4 bits. What the Signal-to-Noise Ratio (SNR) for one of these channels?
5. If you generate a sinusoid of frequency 90 Hz, but only sample your sinusoid at a rate of 100 Hz, what frequency will you hear when you play it?


Home Lab:


The homelab can be found here, after the numbered questions, under the heading "Project". Answer the questions related to this lab and include them with your responses to the Problem Set.

Have fun!

Monday, October 6, 2014

Week 0: Spring Demo

This week, we introduced the course, the Professor, and the TA's. Afterwards, we demonstrated an amplified spring. This gave us an opportunity to talk about some interesting propagation effects. Although we weren't quite ready to explain all the effects mathematically (it was only the first day, after all!), we are well on our way. 


Wednesday, September 24, 2014

Hi there!

Welcome to MUS170 / ICAM103: Musical Acoustics!

Here's a little information regarding the way grades will be calculated:

Attendance - 30%

  • Will be taken each class. In my experience, there is no better marker for class engagement than attendance. 
  • If you know you will miss a class ahead of time, send Tina, Kevin, or me an email in advance and we will spare you, if you deserve it.


Readings -

Generally Puckette's notes (online: http://msp.ucsd.edu/syllabi/170.13f/course-notes/course-notes.html), occasionally also chapters from the Pierce book ("Almost All About Waves"). Pick it up, it's <$20 on Amazon, and a great read.

Assignments - 35%

  • Almost every week there will be a short problem set and home lab.
  • These will generally be assigned on Tuesday in class, due the following Tuesday at class time.
  • This pattern is broken for Tuesday, Nov 18, because the final project proposals will instead be due on that date. The homework for week 6 will be due the following Tuesday, Nov 25.
  • Late assignments will depreciate in value by 10% (not compounding) every 24 hour period.
  • Generally, home labs will be performed in the PureData patching environment (http://msp.ucsd.edu/syllabi/170.13f/lib/index.htm), and we will use the "patch library" Puckette has linked to on this page. You may do the labs as a group, but please submit unique problem sets.


Final Projects - 35%

This project should be completed in groups of 3.

Assignment:

  • Produce a novel musical instrument using the understanding you have gained through this course.
  • The notion of a musical instrument is left intentionally somewhat vague, to permit a wide variety of possible contenders. This instrument could be acoustic, electronic, or hybrid in nature.
  • It should be able to play various "notes" according to the intention of the performer. ie, a maraca or snare drum is not enough. (However, a set of them would be!)
  • You will demo your instrument during the last week of class. you will also write a 3 page paper describing your process.


Your project will be judged on:
  • Originality
    • How novel was your approach?
  • Audacity
    • How many risks did you take? Is it technically challenging?
  • Sound quality
    • How does it sound? Did you succeed?
  • Explanation
    • How did you present it? Did you sell the idea to us?


Final Project Proposal -

  • Each group must turn in a 1 page proposal for the final project by Tuesday, Nov 18.
  • This will count toward 10% of the final project grade, or 3.5% of your raw score.
  • We will give you feedback regarding this proposal, to guide you toward a worthy goal.