This preview shows page 1. Sign up to view the full content.
Unformatted text preview: n transforms an analog input
(such as voltage) into a series of numeric representation by digitization. D/A
conversion is the reverse process of A/D conversion. It transforms a sequence of
discrete numbers back into continuous analog signal. Figure 19.3 shows the role of
A/D and D/A converters in the acquisition and playback of analog signals by a
A multimedia computer system capable of processing audio information requires a
sound board (or sound card), which is equipped with A/D and D/A converters. In
addition to performing the basic function of A/D and D/A conversions of audio
signals, a sound board is generally also equipped with the following features:
1. It has a connector for speakers or headphones to allow users to listen to sound
2. It has a MIDI input port to input sound from an external MIDI device (such as
an electronic keyboard or drums), a MIDI output port to output recorded sound to
the MIDI device, and a MIDI synthesizer to translate the information transferred
between the computer and the musical instrument. MIDI (Musical Instrument
Digital Interface) is an international standard developed for digital music that
determines the cabling, hardware, and communications protocol needed to connect
a computer with electronic musical instruments and recording equipment.
3. Most sound boards also have a volume control knob to allow users to control
sound volume according to their taste.
Digital Audio Quality
The quality of digital audio is characterized by the following three parameters:
1. Sampling rate. Analog-to-digital conversion transforms an analog signal into
a series of numeric representation by digitization. Digitization is composed of
sampling and quantization. Sampling take; snapshots of the analog waveform at certain points in time, and the sampling rate determines how often the analog
signal is digitized. According to Nyquist theorem, the sampling rate must be at
least twice the highest frequency component of the analog waveform to reproduce
the signal optionally. The higher the sampling rate, the truer the sound. Sampling
rate is measur...
View Full Document
This document was uploaded on 04/07/2014.
- Spring '14