 Continuous sequence of vibrations of air  (Why no sound in space? Contrary to Star Wars etc.)  Abstraction of an audio wave:  Ear translates vibrations into sound  The slightest air-pressure fluctuations will move ear drum back and forth

 If you create a sound that vibrates 200 times/second  Send to a speaker, head phone…  Speaker vibrates 200 times in/out in a second

 The number of vibrations (waves), usually per second  Measure: Hertz  Example:  Assume 2 second interval  Vibration of 1,000 times  Cycles/second in Hz?  i.e. how many vibrations in one second?

Assume 1 second

 What is the frequency in Hz?

 Pulse Code Modulation… (DVDs outputs it)  Sample the wave at a specified rate (samples per second)  Sample Rate  Determine the associated amplitude at each sample  Sample value  Store the binary value of the amplitude (sample value)

 Assume one second, one Hz

 Sample Rate = 72 ( measure amplitude 72 times/second)  Sample Size: 4 bits (2^4 = 16 possible values)  So: Every 1/72 of a second, determine amplitude using 4 bits and save as binary

Sample Values: 7,9,11,12,13,14,14,15 etc. Binary nibbles: 0111, 1001, 1011,1100 etc.

 Humans Hearing: 20Hz to 20k Hz  Dogs hearing: 40 Hz to 40k Hz  Voice range 80 Hz to about 4 kHz ( 4,000 Hz)

 Nyquist’s theorem (revisited):  For best pcm result  Sample at 2 x highest frequency  What did we say was the highest frequency of human hearing?  So, what should be the sample rate?  Actually we add 4,100 cycles…thanks to Sony  So final sample rate?

 Sample rate: 44,100/second  Sample size: 16 bits  What is the highest possible sample value?  Sample size for DVDs is usually 24 bits  And we have 5 channels, not two (L,C,R,S1, S2)  Sample rate 96,000 Hz, not the 44,100 as for CD

 Sample rate: 44,100 Hz  Bit depth ( sample size) 16 bits/sample  Allows for 2^16 sample values  Stereo : two channels

 60 seconds x 44,100 samples/second  = 2,646,000 samples  Number of bits to store  2,646,000 samples x 16 bits/sample =  42,336,000 bits  That’s for one channel  For two channels:  42,336,000 x 2 = 84,672,000 bits perminute

 How many bytes?  84,672,000 bits/(8 bits/byte)=  10,584,000 bytes  Kilobytes (KB)?  10,584,000 bytes (1024 bytes/KB)=  10,336 KB  MB?  10,336/(1024 KB/MB) =  10 MB for 1 minute

 Save space  Are Lossless and lossy compression  Some uncompressed audio formats:  WAV, FLAC ( Use wav as master, use mp3 for deployment )  Phone (iphone and Android) format is compressed, lossless (.m4a)  Lossy compressed: mp3  Eliminates sounds we supposedly can’t hear or don’t want to hear

 aiff : non-compressed, pcm  au: compressed, lossy, used by sun, unix, java  wma Windows Media Audio: lossy, compressed

 Html 4 supported formats Html 4  Used embed, object, plug-ins, etc. Very messy  Html 5:  Wav  Mp3  Ogg (vorbis … professional, compressed format)

 Three ways to listen to sounds:  Download and play  Stream  Progressive download  Methods 2 and 3 above yield same results, different technologies  YouTube streams  File usually saved in a Temp folder  iTunes uses progressive  The video file is not stored on the viewer’s computer – the data is played and then discarded by the media player. This lets you maintain more control over your content. Better choice

 If you listen to a radio station online, you will stream the music, since you're listening live and couldn't download all the songs that they play.  Instead, your computer connects to the radio station and receives an ongoing audio feed, or stream, with the radio station's programming.  It begins to play when a sufficient amount is playable. While you listen, more audio is being streamed.  When you stream a file, you will get to listen to or watch it, but won't have the file on your computer to do things with later