Sound Cards

Soundcards Ð'- the basics

Ð'* Core Functions

Ð'- Conversion of analogue signal to digital form for

computer storage

Ð'- Conversion of digitally stored sound information to

analogue form

Ð'* Common Additional Features

Ð'- MIDI control

Ð'- Synthesiser

Ð'* FM mixing

Ð'* Stored samples (wavetable)

Ð'* Software to allow basic control and use of

soundcard features

Ð'* Input is an analogue electrical signal

representing sound

Ð'- Microphone

Ð'- Pickup coil

Ð'- Tape, cd player, instrument, or generator

Ð'* Samples of this are taken at intervals and

converted to digital data

Ð'* Quality and usability dictated by

Ð'- Samples per second

Ð'- Levels per sample

Ð'* Samples per second normally expressed

in kHz

Ð'- More samples give greater accuracy of

waveshape

Ð'- Minimum sample rate = 2 x highest frequency

Ð'* Bits per sample

Ð'- More bits per sample more resolution of

amplitude of waveform

Ð'- 8-bits give 256 levels

Ð'- 16-bits give 65K levels

File size depends on number of bits per sample

and sample rate

Ð'- 11kHz sample rate at 8-bits per sample = 11kB

Ð'- 22kHz sample rate at 16-bits per sample = 44kB

Ð'- 44kHz sample rate at 10-bits per sample = 88kB

Ð'* Note that these are for single channel Ð'- for

stereo you need double the storage.

Ð'* Hence cd quality sound 44.1kHz, 16-bit stereo

needs in the region of 176kB to store ONE

second of sound

Ð'* Digital information from stored file is fed to digital

to analogue converter

Ð'* Output per sample is the amplitude of the

waveform

Ð'* Rate at which samples are played back

determines the time duration

Ð'- Possible to play sample back at different rate from

recorded Ð'- what might that do?

Ð'* Some filtration of output