REC 105/115 Midterm

  1. Velocity of sound:
    1130 ft./second at around 65-68 degrees F
  2. How far does sound travel in one millisecond?
    about 1 ft./millisecond
  3. Formula for the velocity of sound:
    Frequency * wavelength
  4. Reflection:
    sound bouncing off things
  5. Diffraction:
    sound waves bending around things
  6. Diffusion:
    scattering sound that hits in all directions; returning energy back to the room
  7. Phase:
    description of where we are in the waveform, described in degrees
  8. Proximity effect:
    a boost in the bass frequencies when the sound source is close to the microphone (doesn't apply to omni mics)
  9. Doppler effect:
    when a sound's pitch sounds like it changes as its distance changes
  10. RMS:
    root mean square (square root of the mean of squared values)
  11. SCMS:
  12. Dither:
    replacing distortion with random noise (when system starts rounding numbers at low voltage levels)
  13. Transducer:
    a device that changes one form of energy into another form of energy (mic -> electrical signal; electrical signal -> sound from speaker)
  14. Difference between normal and half-normal
    • Normalled means that a signal goes in one place and out one place.
    • Half-normalled means the signal can be split to come out of two places.
  15. How much dB is "twice as loud"?
  16. How much dB is double the power?
  17. How much dB is double the intensity?
  18. How do you reverse polarity on a board?  In a cable?
    • The button with Ø on it reverses polarity.
    • In a cable, switch the connections on the 2 and 3 pin at one end.
  19. Nyquist Theorem:
    your sample rate needs to be at lease twice the highest frequency (20kHz) to accurately reproduce it.
  20. Why is the lowest common sample rate 44.1kHz and not 40kHz?
    A low pass filter is put on the circuit before sampling to eliminate aliasing (harmonic distortion, false frequencies).  A brick wall filter isn't actually possible, so a slightly higher sample rate is needed to account for the slope of the filter.
  21. What does the bottom line of the Fletcher-Munson curves tell us?
    • At 20Hz, the sound needs to be at 60dB SPL to be heard, and increasing the frequency brings down the needed volume quickly. 
    • At 1kHz, 0dB SPL is needed to hear it.
    • From 1kHz to 6kHz, the volume drops below 0dB SPL.
    • After 6kHz, the needed volume goes up.
  22. How well do low and high frequencies travel?
    • Low frequencies travel VERY well and bend easily.
    • High frequencies don't travel very well, get absorbed easily, and don't bend easily.
  23. What happens to the the Fletcher-Munson curves as the volume goes up?
    • they get flatter as you raise the volume
    • the perception of frequency content changes when it gets louder
    • bass frequencies get louder faster
  24. According to the Fletcher-Munson curves, where are our ears the flattest?
Card Set
REC 105/115 Midterm