# REC 105/115 Midterm

The flashcards below were created by user tenorsextets on FreezingBlue Flashcards.

1. Velocity of sound:
1130 ft./second at around 65-68 degrees F
2. How far does sound travel in one 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
 Author: tenorsextets ID: 271797 Card Set: REC 105/115 Midterm Updated: 2014-04-24 23:54:36 Tags: recording Folders: Description: read Show Answers: