• Move a speaker's membrane
• Use an oscillator
• Need a pattern for motion
• Square pattern simplest
• Push out for a while
• Pull in for a while
• The synth applet

Making a better sound

• Use another pattern
• Sawtooth - start silent - gradually louder
• Triangle - gradually louder then softer
• Sin wave - 'smooth' curve

Problems with digital oscillator

• All patterns are blocky
• Limited in X
• Limited in Y
• Even sine is ultimately blocky
• 'pure' audio (analog) is smooth
• 

sampling rate

• What time does one sample represent?
• Measured in Hz (cycles / second)
• Or kHz (1000 cycles / second)
• Faster sampling rate = better sound
• ... but larger file
• represented by distance on time axis
• 

Common sampling rates (approx. quality)

• 8 kHz	bad cell phone
  16 Hz	phone /tr>
  22 kHz	audio tape
  44 kHz	CD

Nyquist's Law

• optimal sampling rate is double desired output frequency
• backwards wagon wheels
• 20 kHz is a high frequency in human range
• Sampling rate is (roughly) 44 kHz

bit depth

• How many possible values for each sample?
• square wave only requires 1 bit / sample
• 8 bits = 256 possible values / sample
• 16 bit = 65,537 possible values / sample
• higher bit depth = better sound
• ... but larger file
• 

Standard bit depths

• 8 bit
• 16 bit
• 32 bit

Quantizing an image

• Use bit depth and sample rate to break signal into digits
• number of values depends on sample rate
• range of each value depends on bit depth
• 

Envelope

• Modifies amplitude over lifespan of tone
• Greatly changes character of tone
• Often measured in ADSR

ADSR Envelope attributes

• A - Attack
• D - Delay
• S - Sustain
• R - Release

Improving the timbre

• Most sounds are more complex than a simple frequency
• You can add multiple oscillators to produce complex sounds