Book Ch 3 Flashcards
What is “sampling rate”
How often a digital sample of an analog source material is taken.
What’s the sample rate of an audio CD?
44.1 kHz / second
What is PCM?
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.
What are the two basic parts of a PCM stream?
Sample rate and bit depth.
What is the Nyquist rate?
Sampling at twice the highest frequency of the signal.
Does sample rate or bit depth determine signal accuracy?
Sample rate! Determines how closely it captures the frequency of the original signal.
Does sample rate or bit depth determine precision?
Bit depth. Determines how close to amplitude values it is.
With 2 bits how many possible states do you have?
4
Bit depth of 16 has how many states?
65,536
What is standard audio CD resolution?
16 bits.
What is a bit used for in audio?
When a sample is taken (determined by sample rate!) the amplitude of the signal is measured in number of bits.
What is bit depth in video?
How many shades can be displayed.
In video 256 colors is what bit depth?
8-bit
What is bit rate?
Quantity of information over time. “bit/s” or “bps”
How many bits in a megabit?
1,000,000 (one million)
Aprox how many states in 32 bit?
4.2 billion
Bit rate of MP3?
128-160 Kbps
Bit rate of Audio CD?
1,411.2 Kbps
Bit rate of DVD?
5 Mbps
Bit rate of HDTV?
20 Mbps
Bit depth vs. bit rate?
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.
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.
Yeah, just read that a few times.
1 frame of uncompressed video at 720 x 480 is how big? How much per minute of video at 30 fps?
About 1 MB. 1.9 GB per minute.
DV cameras tend to compress at a rate of…
5:1
What is a codec?
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.
What is an alternate meaning of “codec”?
A generic term for a videoconferencing unit.
What two elements does a digital file contain?
Container and codec
What’s a container?
Structure of the file. Defines how data is arranged and which codecs are used. Example: WMV (Windows Media Video)
Where does the codec have to be to play a file?
Installed on the OS.
Why is “codec” and names of codecs confusing?
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.
Why is noise more of a problem in analog than digital?
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
A signal that has many varying states is called a _______ signal.
Analog
