Sound Representation

Digitizing Sound Sound waves through Air Different Voltages Voltage converted to numbers

Representing Sound An array of amplitudes (voltage measurements) –Sampling Frequency –Quantization –Dynamic Range

Sampling Frequency How often do we measure the voltage? A sound wave one half as many samples one quarter as many samples

Sampling frequency Like resolution in images –More samples = better quality –Fewer samples = less space

Sampling Frequencies People talking on the phone –10 KHz –10 KiloHertz –10,000 samples per second CD quality music –44.1 KHz Stereo –Two different signals, two different arrays

Quantization How many bits per sample Sound Wave Heavily Quantized

Quantization Speech –8 Bits per sample CD Music –16 Bits per sample Professional quality –32 Bits per sample

Dynamic Range How loud of a noise can you record Dynamic range Exceeding dynamic range

Where are the Words? Janelovesthe dogRalph knowsFred (Phred)

A “sound font” dog Jane knows Fred Ralph the loves Jane lovesFred

MIDI - Musical Instrument Digital Interface Object representation of music Every sound has –Pitch (frequency of the sound) –Delay (how long after last sound start to start playing) –Duration (how long should it play) –Timbre (which instrument should it sound like?) Guitar Clarinet Violin

A MIDI file An array of notes 0 (262, 0,10,1) 1 (300, 10,10,1) 2 (262, 10, 10, 1) 3 (300, 0, 10, 1) Pitch (middle C) Delay Duration Instrument Number During performance numbers are assigned to different instruments

A MIDI file An array of notes 0 (262, 0,10,1) 1 (300, 10,10,1) 2 (262, 10, 10, 1) 3 (300, 0, 10, 1) How do we transpose to a higher key? Increase pitch of each note

A MIDI file An array of notes 0 (262, 0,10,1) 1 (300, 10,10,1) 2 (262, 10, 10, 1) 3 (300, 0, 10, 1) How do we make it play faster? Reduce delay and duration of each note

A MIDI file An array of notes 0 (262, 0,10,1) 1 (300, 10,10,1) 2 (262, 10, 10, 1) 3 (300, 0, 10, 1) How do we change from guitar to flute? Assign a different instrument to that number

Synthesizing an instrument Mix different harmonics Add noise Adjust Attack, Dwell, Sustain, Release

Synthesizing an Instrument Attack - when string is plucked or note is struck Dwell - energy left from attack Sustain - while the note is held Release - after player stops

Synthesizing an Instrument Attack - when string is plucked or note is struck Dwell - energy left from attack Sustain - while the note is held Release - after player stops

Synthesizing an Instrument Attack - when string is plucked or note is struck Dwell - energy left from attack Sustain - while the note is held Release - after player stops

Synthesizing an Instrument Attack - when string is plucked or note is struck Dwell - energy left from attack Sustain - while the note is held Release - after player stops

Synthesizing an Instrument Attack - when string is plucked or note is struck Dwell - energy left from attack Sustain - while the note is held Release - after player stops

Sampled / Object Sampled Jane loves Fred Object