Synthesis Theory I: Midterm



You may use any inanimate resource for this midterm. Your illustrious instructor is the only human you may communicate with about this exam until it is done. The exam is due at 2 p.m. sharp in room 316C before class this Thursday. The exam may not be turned in late.

  1. Ear Physiology: Describe in your own words the anatomy of the ear and how it works to enable us to hear sounds. What are the three basic parts to the ear and what is the function of each part? What is the pinna? What function does it serve in directional hearing? How do we analyze the frequencies of sounds?
  2. Perception of Pitch: What determines the pitch of a soundwave with many harmonic components?
  3. Loudness v Amplitude: Which is louder: (A) a 20 Hz sound at 20 dBSPL or a 200 Hz sound at 19 dBSPL? (B) a 1,000 Hz sound at 50 dB or a 100 Hz sound at 60 dB? (C) a 10,000 Hz sound at 80 dB or a 75 dB sound at 500 Hz? Explain the reasoning/methodology for your answers.
  4. Range of Hearing: What is the highest frequency that you can hear? Hint: use the osc program to write a soundfile with a sinewave that increases in pitch from 1,000 to 22,000 Hz over 21 seconds. Then listen to the soundfile and note at what time the sound becomes inaudible. Use only high quality speakers/headphones such as the Meyer Speakers in room 314C. There are no wrong answers, but I will be testing you myself if I do not believe your answer. List your age and listening environment as well as the highest frequency which you can hear.
  5. Linear Interpolation. You have a soundfile which you want to transpose one octave lower using linear interplolation. Two adjacent samples in the original soundfile have the amplitudes 0.232 and 0.562. There is one additional sample which needs to be placed between these two amplitudes in the final lower-pitches sound. What is the amplitude of that sample?
  6. Just Noticeable Difference: If you have a soundfile which contains whitenoise with a maximum amplitude of 0.5, what is the smallest increase in maximum amplitude necessary to hear the noise increase in loudness? What is the change in decibels for this increase in amplitude? Hint: use the noise generating program from programming lab 1 to determine your answer. Make a note of the listening conditions.
  7. Comb Filtering: If a comb filter has a delay of 100 samples and the sampling rate is 44100, how many times per seconds will the sound cycle through the comb filter delay? If the delay is set to 101 samples, what is the frequency of delay, then? The frequency of the delay cycle matches the pitch heard coming from the comb filter. Speculate on how a pitch could be generated which is between that of the 100 sample delay and the 101 sample delay.
  8. Wavelengths and Hertz: Dolphins are able to produce and perceive sounds in the range from 20 Hz-150 kHz, while people can only hear in the range from 20 Hz-20 kHz. (A) How many more octaves can dolphins hear above humans (approximately)? Dolphins use echo-location to catch prey. (B) How small of a fish can dolphins track underwater? The speed of sound in water is 1,440 meters/second. Assume that the fish must be at least 5 wavelengths of a 130,000 Hz sound to be detected. (C) if a person could echo-locate fish underwater using a 15,000 Hz sound, what is the size of the smallest fish to be detected? How does this relate to the size of the person's mouth? Why can dolphins hear to such high frequencies? If you are intersted in hearing the sounds of dolphins, check out Folkways FW06132: Sounds and the Ultra-Sounds of the Bottle-Nose Dolphin.