Book Ch 3

Question 1

What is “sampling rate”

Answer 1

How often a digital sample of an analog source material is taken.

Question 2

What’s the sample rate of an audio CD?

Answer 2

44.1 kHz / second

Question 3

What is PCM?

Answer 3

Pulse Code Modulation. How audio samples are recorded and stored.

In a PCM stream, amplitude is sampled regularly and each sample is quantized to the nearest value within a range of digital steps.

Question 4

What are the two basic parts of a PCM stream?

Answer 4

Sample rate and bit depth.

Question 5

What is the Nyquist rate?

Answer 5

Sampling at twice the highest frequency of the signal.

Question 6

Does sample rate or bit depth determine signal accuracy?

Answer 6

Sample rate! Determines how closely it captures the frequency of the original signal.

Question 7

Does sample rate or bit depth determine precision?

Answer 7

Bit depth. Determines how close to amplitude values it is.

Question 8

With 2 bits how many possible states do you have?

Answer 8

4

Question 9

Bit depth of 16 has how many states?

Answer 9

65,536

Question 10

What is standard audio CD resolution?

Answer 10

16 bits.

Question 11

What is a bit used for in audio?

Answer 11

When a sample is taken (determined by sample rate!) the amplitude of the signal is measured in number of bits.

Question 12

What is bit depth in video?

Answer 12

How many shades can be displayed.

Question 13

In video 256 colors is what bit depth?

Answer 13

8-bit

Question 14

What is bit rate?

Answer 14

Quantity of information over time. “bit/s” or “bps”

Question 15

How many bits in a megabit?

Answer 15

1,000,000 (one million)

Question 16

Aprox how many states in 32 bit?

Answer 16

4.2 billion

Question 17

Bit rate of MP3?

Answer 17

128-160 Kbps

Question 18

Bit rate of Audio CD?

Answer 18

1,411.2 Kbps

Question 19

Bit rate of DVD?

Answer 19

5 Mbps

Question 20

Bit rate of HDTV?

Answer 20

20 Mbps

Question 21

Bit depth vs. bit rate?

Answer 21

Bit depth is how many computer bits are used for each sample in a waveform - the “resolution”.

Bit rate is the amount of bits conveyed or recorded per unit of time. Often used in compression where you’re losing bits.

Question 22

For example, a sampling rate of 48 kHz and a bit depth of 16 bits means that we take 48 000 equally spaced samples per second of signal, and each of those samples get an integer value between -32 768 and 32 767.

Answer 22

Yeah, just read that a few times.

Question 23

1 frame of uncompressed video at 720 x 480 is how big? How much per minute of video at 30 fps?

Answer 23

About 1 MB. 1.9 GB per minute.

Question 24

DV cameras tend to compress at a rate of…

Answer 24

5:1

Question 25

What is a codec?

Answer 25

A piece of equipment or software using an algorithm to encode or decode files. A codec encodes a data stream for transmission, storage, or encryption or decodes it.

Question 26

What is an alternate meaning of “codec”?

Answer 26

A generic term for a videoconferencing unit.

Question 27

What two elements does a digital file contain?

Answer 27

Container and codec

Question 28

What’s a container?

Answer 28

Structure of the file. Defines how data is arranged and which codecs are used. Example: WMV (Windows Media Video)

Question 29

Where does the codec have to be to play a file?

Answer 29

Installed on the OS.

Question 30

Why is “codec” and names of codecs confusing?

Answer 30

Codec can mean the codec IN the container or the container, and codec names can mean either codec or a container. AVI container can use an MPEG codec.

Question 31

Why is noise more of a problem in analog than digital?

Answer 31

Signal loss in analog means there’s less signal in comparison to noise, so when you amplify back up to original levels you amplify the noise, too.

With digital it’s either there or it isn’t so there’s no noise to amplify

Question 32

A signal that has many varying states is called a _______ signal.

Answer 32

Analog