SOUND Sound Continuous sequence of vibrations of air

SOUND

Sound? � 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 �

Speakers � � 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

Frequency � � � 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?

Cycles: Example of Two Hz Assume 1 second

Hz? � What is the frequency in Hz?

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

Example � Assume one second, one Hz

Made up Sample Data: Assume � � � 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

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

Common Ranges � � � Humans Hearing: 20 Hz to 20 k Hz Dogs hearing: 40 Hz to 40 k Hz Voice range 80 Hz to about 4 k. Hz ( 4, 000 Hz)

Frequency and sampling � � 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?

CDs � � 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, S 1, S 2) Sample rate 96, 000 Hz, not the 44, 100 as for CD

Storage of 1 minute stereo music on a CD � � Sample rate: 44, 100 Hz Bit depth ( sample size) 16 bits/sample � Allows � for 2^16 sample values Stereo : two channels

Total number of Samples (for 60 seconds) � 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

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

Compression � � � Save space Are Lossless and lossy compression Some uncompressed audio formats: � WAV, FLAC ( Use wav as master, use mp 3 for deployment ) � � Phone (iphone and Android) format is compressed, lossless (. m 4 a) Lossy compressed: mp 3 � Eliminates sounds we supposedly can’t hear or don’t want to hear

More audio formats � � � aiff : non-compressed, pcm au: compressed, lossy, used by sun, unix, java wma Windows Media Audio: lossy, compressed

Power. Point support

Audio and the Web � Html 4 supported formats � Used � embed, object, plug-ins, etc. Very messy Html 5: � Wav � Mp 3 � Ogg (vorbis … professional, compressed format)

Web Streaming versus downloading (Video and Audio) � Three ways to listen to sounds: � Download and play � Stream � Progressive � � Methods 2 and 3 above yield same results, different technologies You. Tube streams � File � download usually saved in a Temp folder i. Tunes 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

Streaming � � 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