Development of a Digital Audio Card for Recording and Playback on Personal Computers

Abstract

The development of communication interfaces for personal computers and related equipment presents one of the most challenging problems in the electronic industry today. This research work will provide a high speed procedure of recording and playing back of audio signals at a relatively reduced cost. The developed system uses a personal computer to control and synchronize all the input/output (110) operations of the audio card. It will increase the versatility of the microcomputer systems and provide a suitable means of audio signal acquisition, storage and its retrieval. The developed system consist of two sections; a software section and a hardware section. The hardware consist of a digital audio card circuitry interfaced to a personal computer via its parallel port. The circuit card was developed in a modular fashion comprising of three modules, namely; the recording module, the playback module and the power module. The recording module utilizes an 8-bit analog-to-digital converter IC, configured to accommodate a sampling frequency of approximately 44. IKHz, thus allowing the use of an economic reconstruction filter. The digitized audio signal could be stored in a floppy disc or the hard disc (depending on the specification in the software driver) for subsequent playback. The playback module uses an 8-bit digital-to-analog converter IC The power module provides the four stabilized voltage levels; + 15.0V,-15.0V, +5.0V and-5.0V. A menu-driven software package written in C++ for the 110 control of the audio card was developed The software driver can broadly be divided into the following three modules; the menu module, the recording module and the playback module. A graphical display interface that displays the relative amplitude of the instantaneous audio signal (during recording or playback mode) is incorporated in the menu module. The recording module controls the sampling time of the ADC and the storage of the digitized signal, while the playback module controls the signal reconstruction frequency, the retrieval of the stored digital signal for subsequent transmission to the DAC circuit. The software driver was used to carry out preliminary system performance tests in the computer hardware laboratory to simulate the recording and playback of baseband audio signal, using generated pseudo-random signal values. The developed audio card may be used for data storage, data archiving. A commercial application of the card is its use as repeaters; whereby audio signals are recorded and playback at intervals. Digital repeaters may be used in a train station or a supermarket for advertisement. This will eliminate the rewinding time as in the case of analog ones, will result in reduced tape wear because the read head is contactless, and the playback will possess the same quality as in the.