12 - Acoustics 2 - Speech Recordings

Question 1

When recording speech audio, your frequency range should be at least 70 - ___ Hz

Answer 1

8000

Question 2

Why are headset microphones usually preferred over handheld/clip-on/built-in mics?

Answer 2

They reduce the effects of background noise and head movement effects on intensity

Question 3

Which mics are usually more sensitive and responsive: condenser or dynamic?

Answer 3

Condenser

Question 4

Balanced XLR connectors are the 3 prong microphone connectors found on professional microphones. These are better for _______ than 3.5 mm connectors.

Answer 4

Balanced XLR connectors are better for reducing electronic noise

Question 5

What are omnidirectional microphones good for?

Answer 5

Capturing ambient noise, outdoor environments, concerts, etc.
-good for if the sound source is moving and the microphone is stationary

Question 6

Omnidirectional microphones can prevent “______ effect” that can occur with directional microphones

Answer 6

Proximity Effect

Question 7

Directional mics are good for minimizing __________

Answer 7

Feedback noise

-directional (cardioid/heart-shaped) mics are good for speech recordings that require low noise levels (better SNRatio)

Question 8

Which type of microphones, omnidirectional or directional, need to be used at the correct distance to avoid proximity effect?

Answer 8

Directional

Question 9

_____ ______ is a phenomenon that leads to an increase in low frequency response as you move the mic closer to the source

Answer 9

Proximity Effect

Question 10

True or false: for microphones, you want to select as flat a frequency response as possible

Answer 10

True

Question 11

True or false: for speech audio recording levels, you want to adjust the levels to extreme high and low levels

Answer 11

False - adjust recording levels to the middle amplitude range of your recorder

Question 12

For speech audio recordings, are uncompressed .wav digital file formats better or worse than compressed formats, such as mp3?

Answer 12

better

Question 13

Name 2 of the 4 things to consider related to digitizing speech into computers

Answer 13

• analog vs digital
• sampling rate
• filtering
• quantization

Question 14

What is the rule for determining sampling rate?

Answer 14

Sampling rate must be more than 2x the highest frequency of interest

Question 15

What is the highest frequency of interest for speech? What does this mean our sampling rate should be?

Answer 15

Consonants (10,000 Hz)

Sampling rate should be more than 20,000 Hz

Question 16

What is aliasing caused by, and how do we prevent it?

Answer 16

Caused by undersampling the higher frequencies

-prevent this by filtering the signal with a low pass filter set at 1/2 the sampling frequency, before you digitize it

Question 17

What is “quantizing”?

Answer 17

The coding of the signal’s amplitude at each point in time (relates to dynamic range)
-more bits = more amplitude levels available for storage
- bit = N
quantization levels = 2^N

Question 18

How many bits are recommended for digital speech?

Answer 18

At least 12

24 if the speech involves large changes in in intensity