Sound is a single waveform which can be decomposed into pure frequencies. For example, the music of a rock band is a single waveform. Physiologically, however, the listener hears the different instruments and the voice. In its natural state sound in an analog phenomenon-that is a wave phenomenon. By measuring the single waveform at frequent intervals and representing each measurement as a binary number analog sound can be digitized.
The quality of digital sound depends on the frequency at which the sound is measured as well as the size of the word used to represent the wave form. To convert the voice into a telephone quality binary signal the voice is sampled 8000 times a second. The measured waveform is converted into a seven bit binary number with an eighth bit added for error checking. This means a telephone conversation is converted into a stream of 64,000 bits per second. The telephone system is presently analog between telephones and the switchboard, but an increasing portion of long distance phone traffic is being sent digitally. The phone conversation is converted at the telephone exchange (switch) prior to long distance transmission. In the future all telephone conversations will be converted to digital at the phone.( 10 to 30 years) Corporate internal communications are rapidly becoming digital so that the corporation can use the installed telephone lines for simultaneously voice and data transmission. In order to obtain stereo quality sound you need a larger word size (16 bits) and much more frequent sampling to capture the high frequency sounds. One scheme for digital recordings measures the sound 44,000 times a second using a 16 bit( 2 byte) word for 1.4 million bits a second. The new stereo sound TV samples about 36000 times a second and used a 14 to 16 bit word for the measurements.
Surf the Internet: For a very nice page created by MCI demonstrating the affect of the frequency of measurement on the quality of sound, click here. This demonstration requires a multimedia computer for full effect. When finished, click on `back' at the top of your Netscape screen.