How Analog and Digital Recording Works Analog converted to digital via an ADV (Analog to Digital Converter = stream of numbers) On playback: digital converted to analog wave via a DAC (Digital to Analog Converter) Digital never changes (unless corruption occurs)

How Analog and Digital Recording Works What are the two variables that affect the quality? 1) Sampling rate - samples per second Higher sample rate = higher fidelity Usually 44,100 SPS for CD 2) Sampling precision - sample accuracy Higher precision = higher fidelity Usually 65,536 Sampling error = detail missed in conversion

Sampling precision What's so special about 65,536

Sampling precision What's so special about 65,536 On a CD each sample is recorded as a binary number up between 1 and 65,536 This number is written in binary code in two bytes (16 bits) / bit = binary digit What's this number?

Sampling precision 0 = = = 0 4 = = = = = 10100

How File Compression Works What's the point of compression? (why do we need it?)

How File Compression Works Reduce redundancies (number of bits and bytes in file) In John F. Kennedy's 1961 inaugural address, he delivered this famous line: "Ask not what your country can do for you -- ask what you can do for your country.“ 17 words - 61 letters, 16 spaces, one dash and one period. If each letter, space or punctuation mark takes up one unit of memory, we get a total file size of 79 units. "ask" appears two times "what" appears two times "your" appears two times "country" appears two times "can" appears two times "do" appears two times "for" appears two times "you" appears two times Ignoring the difference between capital and lower-case letters, roughly half of the phrase is redundant.

How File Compression Works Reducing redundancy is about finding patterns (LZ adaptive dictionary-based algorithm) 1. ask 2. what 3. your 4. country 5. can 6. do 7. for 8. you 1 not (74 units)

How File Compression Works Reducing redundancy is about finding patterns (LZ adaptive dictionary-based algorithm) 1. ask__ 2. what__ 3. you 4. r__country 5. __can__do__for__you 1not__2345__--__12354 (59 units)

Lossless vs Lossy Compression Do you know the difference?

Lossless vs Lossy Compression Do you know the difference? Lossless = exact file Lossy = not exact file. (Original file cannot be reproduced / not for programs, etc).

Audio File Formats What file formats do you know? Why do you think we have so many different audio, image and video formats?

Audio File Formats Audio file is defined by two factors: 1. File type - most common are Wave files (wav) and MPEG Layer-3 files (mp3) Container - packaged, transported, and presented 2. Codec - way the audio is compressed and stored (different file types may use the same codec) Compressor - decompressor Open file formats - playable on most devices E.g., wav, mp3 Proprietary formats - may include DRM (Digital Rights Management) or other copy protection E.g., wma, aac Compression (eliminating parts that are inaudible)

Image File Formats What file formats do you know?

Image File Formats Different file types (compress image in different ways) Main - Tiff, Jpeg Binary (on off / 0 1) 1 bit colour (2 / white or black) 2 bit (4) 3 bit (8) 8 bit (256) TIFF - lossless (usually) or lossy / usually large file size (little or no compression / LZW). JPEG - discards information eye will not notice (24 bit color / good compression) High quality digital photographs. PNG - lossless (exactly reversible / looks for patterns) GIF - Selects 256 colour pallet (16 million, lossless 256) / More than 256 (blends) RAW - lossless, smaller than TIFF / varies by manufacturer (camera). BMP - uncompressed, proprietary (MS) / do not use PSD, PSP - proprietary (layers) / may be obsolete when software updates. Use for editing

Video File Formats What file formats do you know?

Video File Formats Some video formats are more compatible than others (codec = compression) Popular containers (Quicktime MOV, Windows AVI, Flash FLV, MPEG4 MP4, Windows WMV) Packages - video stream, audio stream, metadata, subtitles and chapter- information WMV, AVI, Quicktime - higher quality, higher file sizes. WMV - Windows only, Mac with player AVI - Windows only, Mac with player Quicktime - both MPEG - (MPEG 1 - video CD's, MPEG 2 - broadcast / DVD, MPEG 4 - Digital Rights Management / copying) H codec for HD/Blu-Ray YouTube - H.264/MPEG-4 AVC format, with stereo AAC audio High quality, low bit rates = smaller file DivX - different codec / Still high quality, small file, lossy

Exporting for use on the Web Find balance (quality v file size) Video (mobile kbps, DVD kbps) Export to.swf for animations, regardless of the program you're using!