Digital Audio

A/D and D/A

• A/D=analog to digital conversion. Turing vibration into binary code (mic to recorder or DAW)

– Conversion of continuous signal to a discrete one

– Continuity to discrete steps

• D/A=digital to analog conversion. Turn code into vibration (DAW or recorder to monitors (headphone and speaker))

• Most recording devices (computer or recorder) have both devices

Sampling Rate• Measured in KHz

– 32KHz, 44.1KHz, 48KHz, 96KHz, 192KHz

– How many times per second a waveform is “analyzed”

• Measures amplitude over time

• Higher the sampling rate the more accurately the sound is reproduced digitally

• Higher the sampling rate, more processing in post

• Essentially, it deals w/ the highest reproducible frequency

• Represented horizontally in digital waveform

Nyquist Theorem

• In order to reproduce a sound waveform as a digital waveform, the sampling rate must be at least TWICE frequency of of the sound being captured

• Human hearing range???... 20KHz

• Aliasing=new frequencies appear and distort original signal

• Image aliasing...resolution

Bit Depth

• Aka “quantization”

– How amplitude is represented as binary code

• Determines the dynamic range

– Can capture quieter sounds, louder sounds, and sound with less noise

• 1 bit = +6dB of dynamic range

– 16 bit resolution= 16 x 6= 96dB of dynamic range

• Represented vertically in digital waveform

Sampling Rate + Bit Depth

• More/less information

• Allows for more/less processing

• More/less dynamic range

• More/less disk space

• More/less accurate digital representation

• DVD Audio/Blur-ray=96KHz 24 bit

• Broadcast audio=48.1KHz 16bit

• CD audio=44.1KHz 16 bit

Sampling Rate + Bit Depth Cont'd

• Bit depth + sampling rate + time = file size

• 96KHz is 200% larger than 48KHz

• 24bit is 300% larger than 16bit

Formats

• MP3...NEVER EVER EVER USE THIS!

– Compressed to 1/10 the size of a .WAV or .AIFF

– Made for sharing

– Don't record EVER in this format

– Use format for sharing larger files

• .WAV = Microsoft's proprietary format

• .AIFF = Apple's proprietary format

• WAV/AIFF are “lossless audio”