Digital Media Flashcards
What is a transducer?
- Electronic device that converts energy from one form to another
What are examples of transducers?
-Microphones, loudspeakers, thermometers, position and pressure sensors and antenna
What does a transducer do?
- Converts audio (sound waves-analog) to electrical signals (digital) that can be stored in a computer
What are two ways of creating audio?
- Sampling
2. Synthesis
What is sampling?
- A step used in converting an analog signal to a digital signal
What is synthesis?
- Artificial sound produced from mathematical equations
What are the two steps of sampling?
- Take snapshots are regular intervals
- Truncation or Quantization: Lossy compression technique achieved by compressing a range of values to a single quantum value.
What is a period?
- The time interval between two waves
How to find the amplitude and what it does relate to?
- The distance between the center line of the function and the top or bottom of the function,
- Relates to intensity of sound (loud or soft)
What is frequency?
- Describes the number of waves that pass a fixed place in a given amount of time.
How to find the frequency?
1/ period
What is frequency related to?
- Perceived pitch
What does phase relate to?
- Can depend on the relative location of the sound
What is dB-SPL(sound pressure level) equal to?
20 log10 (sound/threshold)
What is the frequency limit that humans can hear?
16-20 Hz and as people get older, the range becomes lower
What does digitizing sound involve?
-Involves taking samples (measurements) at a fixed rate (sampling rate) and recording them
What does the Nyquist Shannon Therom state?
- The sampling rate must be equal to or greater than twice the highest frequency in the signal.
- The period or interval of your sample should be less than half of the original signal
What are three examples of CODECS
- FLAC (Free Loseless Audio Codecs)
- MP3 (Moving Pictures Experts Group)
- AAC (Advanced Audio Coding)
What is FLAC? (only lossless)
- Most common lossless algorithm but it not as effective
- Used for archiving high quality audio
What is MP3?
- Lossy compression
- Uses psychoacoustics, Huffman encoding, and lower bit rates
- Popular on most mobile devices
What is AAC?
- Lossy compression
- Uses psychoacoustics, Huffman encoding, and lower bit rates
- Better perceived quality than MP3
- Popular on Apple devices and most smartphones
What are three types of audio compression techniques?
- Lossy
- Lossless
- Codecs
What is lossless audio compression?
- Compression technique that does not lose any data in the compression process.
What is lossy audio compression? (2 points)
- Delete data that your ears can’t perceive in order to make files easier to transfer over the internet.
- Reduce bit rate (less accurate reproduction of the original)
Codecs (2 points)
- Device or software that is used to compress or decompress algorithms for audio and video
- It’s job is to organize data in the media file
What was the only practice way to store massive amounts of data?
- Videotape
Bit Rate (2 points)
- Number of bits that are translated or processed per unit of time ( every second)
- Bit rate: sampling rate x bit depth
What does a higher bit rate mean?
- Higher bit rate = better quality = larger file size
Bit depth
-how many bits are used for each sample
What is uncompressed audio stored in?
- Saved in a .wav format
What does a higher bit depth mean?
- More accurate sample
What is quantization noise?
- Difference between what the signal was vs. what the signal was recorded as
Bits <8
-Not used for sound
- Can be used to record physical processes like
blood pressure, heartbeat, motion due to walking or running
8 bits
- Common in telephony
- Quantization noise can be perceptible sometimes
16 bits
- Most high-quality sound (CDs, DAT, MP3, movie audio tracks)
24+ bits
- Even higher quality/dynamic range (DVD-Audio, DTS)
- Often used before or during sound processing/editing (mastering)
Name 4 colour models
- RGB
- Cyan, Magenta, Yellow, and blacK (CMYK)
- Hue, Saturation, Luminance (HSL)
- Luminance, Blue, Red (YUV)
How many hexadecimal are in 1 byte for RBG Model?
- Two hexadecimals
How many bits are in each channel for RBG Model?
-There are 3 -8 bit channels, 24 bit colour
How many bytes are in each of the RBG components?
- 1 byte which is 3 bytes per pixel
What is a pixel?
- Dots of colour in an image (or on a display)
What is resolution?
- Number of pixels in an image (or on a display)
- Size of an image, measured in pixels
Sometimes refers to the pixel density, the number of pixels per unit of distance (e.g., pixels per inch or ppi)
What are Vector Graphics?
- An image that is defined using mathematical equations representing lines, curves, and polygons
What does each pixel represent?
- Single colour and represents RBG
The benefit of vector graphics?
- Can be enlarged without loss of detail or change in file size
How are vector graphics created?
- Created through drawing applications or text editors
What is SVG (Scalable Vector Graphics)?
- Popular vector graphics format and are text-based
What are Raster Graphics?
- An image that is comprised of a matrix of pixels
What are examples other than SVG that are examples of vector graphics?
- Computer fonts
2. Geometric shapes in various shapes
How are raster graphics?
- Images created/edited using painting applications
Disadvantage of Raster Graphics
- Good for photographs but suffers from pixelation
What is a popular technique for compressing images?
-Indexed colour- Instead of representing all colours, save only those used (or those that are most useful to keep
What type of encoding is similar to Indexed colour?
- Keyword encoding but with colours instead and with some colours possibly removed
What are some examples of image formats?
- GIF
- PNG
- JPEG
What is a GIF and type of compression? (3 points)
- Graphics Interchange Format
- Lossless, indexed colours (maximum of 256), coding related to Huffman’s
- Allows transparency and animation
- low quality
PNG + Type of Compression
- Portable Network Graphics
- Lossless compression using indexed colours, run-length encoding
- Allows transparency and more modern
What are PNG and GIF best used for?
- line drawings, logos, or diagrams
JPEG + Type of Compression
- Joint Photographic Experts Group)
- Lossy compression technique (only one)
What is JPEG good for?
- Great for photos, bad for images with text or sharp lines
- Reduce colour resolution (sharp colour transitions less
noticeable than to sharp brightness transitions)
What is a compression artifact?
- Noticeable distortion of media caused by the application of lossy compression.
Challenges with using Virtual Reality (four)
- Processing power
- More complex hardware
- Images need to be generated much faster than movies
- Cannot be used for too long
What is a video comprised of?
- Comprised of frames of still images (combined with audio)
What are two video compression techniques?
- Spatial (Intra-frame) (e.g., M-JPEG)
2. Temporal (Inter-frame) techniques
What is Spatial Compression? (2 points)
- Intra frame technique (compression is done within that single frame)
- Use information from within the same frame to reduce file size
What is temporal compression?
- ## Use data from nearby frames (before or after) to reduce the file size
How are key frames compressed?
- typically compressed using only spatial technique
What are key frames and how are they reproduced?
- defines the starting and ending points of any smooth transition
- can be reproduced independently
Where are keyframes inserted?
- inserted automatically at scene changes and/or at regular intervals to preserve quality of streaming or playback
What are P frames? (predictive)
- Frames can use data from previous frames to decompress and are more compressible than I‑frames
What are B frames? (Bidirectional)
- Frames can use both previous and forward frames for data reference to get the highest amount of data compress
What happens if bitrate becomes too low?
- The video becomes pixelated
What is variable bit rate?
- Allows higher bitrates during fast motion scenes, and lower bitrates when there is little motion
- A control technique which allows the bit rate to vary, but maintains the quality
What is control bit rate?
- A control technique which keeps the bitrate constant, but allows video quality to vary.
Examples of 4 Codecs
- HuffYUV
- MPEG-2
- H.264
- H.265 (HEVC)
What is HuffYUV?
- a codec that uses lossless compression (Huffman encoding)
MPEG2?
- a codec that uses lossy temporal and spatial compression and Huffman encoding
What is H.264?
- a codec that uses lossy, temporal and spatial compression for frame prediction
- Perceived quality higher than MPEG-2 at same bitrate
What is H.265 (HEVC)
- a codec that is lossy, 50% reduction is size from H.264
- more complex and drains battery faster
What is a file container?
-Combine a video stream and an audio stream into one file
What type of additional data does file container allow for ?
- optional subtitles
- Multiple language audio tracks
- Additional video stream representing different viewing angles
What is.avi? (Audio Video interleave)
- a container that is very old not good for streaming
What is .mp4? (MPEG4
- a container that supports multiple audio/video streams and subtitles, but limited codecs
- very popular on mobile devices
What is mkv (Matroska)?
- a container that is like like mp4, but supports unlimited streams and unlimited codecs
- support on mobile devices varies
Name 4 video editors
- iMovie ((macOS, iOS)
- OpenShot (Linux, macOS, Windows)
- VSDC Free Video Editor (Windows)
- Adobe Premiere Pro (macOS, Windows; professional app)
