REC 105/115 Midterm

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Author:
tenorsextets
ID:
271797
Filename:
REC 105/115 Midterm
Updated:
2014-04-24 19:54:36
Tags:
recording
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  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"?
    +10dB
  16. How much dB is double the power?
    +3dB
  17. How much dB is double the intensity?
    +6dB
  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?
    80-90dB

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