WO1996029641A1

WO1996029641A1 - Compact disk read-only memory with integrated sound card

Info

Publication number: WO1996029641A1
Application number: PCT/US1996/003783
Authority: WO
Inventors: Dan Kikinis
Original assignee: Elonex Technologies, Inc.
Priority date: 1995-03-23
Filing date: 1996-03-21
Publication date: 1996-09-26

Abstract

An integrated CD-ROM unit (30) combines the electronics and functions of a sound card (24) within the structure and shielding of a CD-ROM drive (34) having all of the usual CD-ROM drive electronics (16). An analog sound cable (22) and one digital to analog converter (26) are eliminated, and direct controlled analog audio signals are output from the CD-ROM enclosure (32) for driving one or more speakers. In one alternative, a conventional IDE interface (14) from a system bus (12) drives the integrated CD-ROM and sound electronics unit, and a CPU connected to the system bus executes dedicated proprietary driver routines for operating the integrated unit. In another alternative, the CPU executes conventional driver routines, and registers are selected in either the CD-ROM circuitry or the sound control circuitry by a select line in a proprietary communication interface connected to the integrated unit and the system bus.

Description

COMPACT DISK READ-ONLY MEMORY WITH INTEGRATED SOUND CARD

Field of the Invention

The present invention is in the area of drives for compact disk read-only memory (CD-ROM) media, and pertains in particular to processing audio signals in conjunction with such drives.

Background of the Invention

CD-ROM drives have become, by the time of this specification, commonly available in personal computer (PC) systems. There are several advantages to CD-ROM memory systems when compared to more traditional forms of archival-type storage. For example, a CD has an ability to store relatively large amounts of data. Also, a CD has an optical interface. For certain types of data, such as audio (sound) data, both may be distinct advantages. To produce high quality sound, a relatively great amount of data space is required. An analogy might be made to high quality image storage, which also requires relatively high density data. The commonality is in resolution. In addition, an optical interface provides higher quality sound by virtue of a clean interface to the media data.

In addition to high density, high capacity storage and a clean interface, good sound quality is also dependent, to some extent, on signal to noise ratio (SNR). The larger the signal to noise ratio, that is, the greater the signal level in relation to the noise level, the better the sound quality may be expected to be. By improving (increasing) SNR for a sound system, sound quality will improve. In general, it is desirable for a sound system to maximize SNR. - 2 -

In a conventional PC having a CD-ROM drive, a sound card associated with the computer controls sound output by interfacing with and accepting commands from the central processing unit (CPU) of the computer over a system parallel bus, and by processing analog audio data sent on a dedicated cable from the CD-ROM drive according to the instruction from the CPU. The sound card has an amplifier responsive to digital commands for controlling gain,

In this conventional arrangement, sound cards of relatively widely variant quality may be used , depending on the baseline SNR associated with the sound card. Superficially, then, it might be assumed that sound quality from a sound card is easily controllable. This might be so if SNR were the only controlling factor. In practice, however, there are many factors other than SNR that may affect sound quality. One such factor is external ambient noise sources which are capable of degrading baseline SNR for a sound card. By coupling into the electronic circuitry of a sound card, such as a digital to analog converter (DAC), which is a common component, external ambient noise adds to the noise generated internally by the electronic circuitry of the sound card. This phenomenon raises the overall noise level on a sound card and consequently lowers SNR. It is seen, then, that the environment in which a sound card is placed can affect output sound quality for the system using the card.

As an example of ambient noise reducing sound quality for a system, consider operation of such a sound card in an active PC. A PC, as is generally known, is an inherently noisy system. Within the housing of a conventional PC, there is at least one conversion power supply converting primary AC power to DC at voltage levels needed by the computer elements and components. There is also a large amount of digital logic performed by various integrated circuit devices, such as a microprocessor-based CPU. The switching nature of power supplies and the fast signal edges associated with digital logic are significant external ambient noise sources, and may radiate noise throughout a PC system. Furthermore, the conventional placement of a sound card in an expansion slot in the architecture of PC, unshielded from all these noise sources, is virtually certain to degrade SNR for a sound card, and the therefore adversely affect output sound quality.

The placement of a sound card in an expansion slot in a system architecture also physically separates the sound card from a CD-ROM drive from which it must access sound data. Because of this separation, an analog sound cable is required to connect the sound card to the CD-ROM drive in order to transport sound data, which results in high cost for sound card usage. In addition, this conventional placement of a sound card in a PC generally results in connectors to a sound card, such as for microphones and headphones, being placed in the back of the system housing. This placement might be less convenient than having such connectors in the front panel of the system housing.

It is seen then, that there are disadvantages accruing from the conventional placement of a sound card in a PC expansion slot, which leads to its physical separation from a CD-ROM drive. This conventional placement not only exposes a sound card to high ambient noise levels that degrade SNR, and hence output sound quality, it also results in high cost for sound card usage and less than ideal location of connectors for headphones and microphones.

It is well known that a CD-ROM drive is typically located in the front panel of a PC system housing, providing easy access for loading and unloading CD media. Also, a CD-ROM drive is a self-contained unit in a sheet metal casing which serves to shield internal elements from high ambient noise levels that exist inside a PC system housing. This shielding provides an advantage for the signal processing circuitry of CD-ROM drive over the audio processing circuitry of a sound card.

Typically, the sheet metal casing of a CD-ROM drive is connected to the PC housing, which is electrically grounded. This connection allows the sheet metal casing to divert towards ground all ambient external noise that couple to it, providing for a low noise level environment within the sheet metal casing.

Being a self-contained modular unit, a CD-ROM drive also contains its own DAC for sound data processing. So, when a CD-

ROM drive is used with a sound card associated with a PC, the DAC in the CD-ROM is a redundant component. This redundancy adds to the cost for sound card usage, as there are two identical components with only one being used. In this arrangement, sound data is retrieved from a CD disk by laser technology, converted to analog audio signals, transported to the sound card on an audio cable, reconverted to digital form for processing in the sound card electronics, then converted again to analog audio form, and finally output at the speaker set connected from the sound card. Thus, in addition to the disadvantages and costs described above, associated with the location of a sound card and physical separation from a CD-ROM drive within a PC, further unnecessary costs are incurred due to element redundancy.

What is clearly needed is a CD-ROM with sound card electronics physically located within the housing of the CD-ROM, resulting in a CD-ROM drive with integrated sound card electronics. Such a unit would provide improved output sound quality, lower cost, and improved user access and interface. By integrating the sound card electronics within a CD-ROM drive's housing, the effect of external ambient noise sources will be minimized, raising SNR for the sound card electronics (now shielded from PC ambient noise) and improving its output sound quality.

In integration of sound card electronics with a CD-ROM in the CD-ROM's housing, which is according to the present invention, there are several alternatives. In one alternative, sound card electronics may be placed on the printed circuit board (PCB) in the CD-ROM assembly without major alteration, and a single trace may be implemented on the PCB to provide the function of the analog cable needed in conventional systems. In another alternative, the digital circuitry for the sound card electronics may be connected to digital circuitry for the CD-ROM drive by digital signal pathways. In a third alternative, the digital electronics for the sound card and for the CD- ROM drive may all be provided on a single application-specific integrated circuit (ASIC).

Brief Description of the Drawings

Fig. 1 is a block diagram illustrating a conventional sound card and CD-ROM drive system in a PC.

Fig. 2A is a block diagram illustrating a CD-ROM drive with integrated sound card electronics according to an embodiment of the present invention.

Fig. 2B is a block diagram illustrating an alternative integration of sound card electronics with a CD-ROM drive according to the present invention.

Fig. 3 is a block diagram presenting a more detailed view of an embodiment of the present invention showing hardware compatibility with existing PC systems.

Fig. 4 is a block diagram of an embodiment of the present invention showing software compatibility with existing PC systems. Fig. 5 is an alternative block diagram of the system shown in Fig. 4.

Summary of the Invention

In a preferred embodiment an integrated CD-ROM sound processing unit is provided, comprising a CD-ROM drive, including a laser read head and tracking apparatus; drive electronics circuitry connected to the CD-ROM drive for operating the CD-ROM drive and for retrieving digital data from the laser read head; and sound electronics circuitry connected to the drive electronics. In this configuration, the sound electronics circuitry and the drive electronics are enclosed in a shielding enclosure, and the sound electronics circuitry receives sound data from the drive electronics circuitry and provides analog sound signals to an external connector through a digital-to-analog converter (DAC). The integration of a sound card in a CD-ROM drive saves one digital-to-analog controller and eliminates the audio cable typically used to transport audio sound data from the CD-ROM to the sound card at a different location in the computer. Signal-to-noise ratio for the sound card circuitry is improved, because all of the sensitive circuitry is now shielded, and controlled and amplified sound output may now be made from the CD-ROM enclosure typically implemented in the front of a computer case.

There are three integration alternatives. In a first arrangement, the electronics implementation for the CD-ROM drive and for the sound card electronics is essentially unchanged. The sound card electronics is mounted on the printed circuit board of the CD-ROM drive and a single trace is used to connect the analog output of the CD-ROM drive electronics (formerly routed to the analog cable) to the analog input of the sound card electronics, which is configured to convert the analog audio signals back to digital for processing by the sound card electronics.

In a second integration alternative, the redundant DAC of the CD-ROM electronics is not used, and may be eliminated. In this alternative, the CD-ROM electronics and the sound card electronics are implemented separately, but the output of the CD-ROM electronics is digital, and a digital link is implemented on the PCB between the CD-ROM electronics and the sound card electronics. In a third integration alternative the CD-ROM electronics and the sound card electronics are fully integrated in a single ASIC, eliminating the need for either a digital or an analog link from the CD-ROM drive electronics and the sound card electronics external to the ASIC. Similarly, there are at least two alternatives for compatibility between an integrated unit according to the invention and the conventional hardware and software of a host PC. In one communication alternative, communication from the system CPU to the integrated unit is through a conventional Integrated Drive Electronics interface, and the system CPU executes special proprietary driver routines. In a second alternative embodiment, the system CPU executes conventional routines used for communication with a separate sound card and CD-ROM drive, and the bus interface has an extra address line for selecting either a CD mode, to communicate with the CD control and data registers, or a sound control mode, for communicating with the registers associated with the sound control electronics.

Description of the Preferred Embodiments In embodiments of the present invention, sound card electronics are integrated with a CD-ROM drive with the sound card electronics within the sheet metal casing of the CD-ROM drive. The metal casing of the CD-ROM drive provides shielding from ambient noise, and the location of the card with the CD-ROM drive affords a cost savings by avoiding the use of a sound cable for audio sound signal transport from a CD-ROM drive to a sound card elsewhere in a PC system, and also avoiding use of a redundant DAC. Furthermore, the typical location of a CD-ROM drive in the front panel of a PC system housing permits connectors for microphones and headphones to be brought out to the front of a PC system, improving user access.

Fig. 1 is a block diagram depicting a conventional sound card and CD-ROM drive system 11 in a PC, showing the physical separation and interconnections between a sound card 13 and a CD-ROM drive 27. Sound card 13 is placed in an expansion slot connected to a bus structure of the PC system in this example. Industry Standard Architecture (ISA) bus 23 is the main data and command link in the PC, and allows communication between different subsystems, such as a CPU 22 mounted on a motherboard 20, CD-ROM drive 27, and sound card 13.

In the conventional arrangement shown in Fig. 1. sound card 13 receives commands from CPU 22 on motherboard 20 connected also on bus 23, through interface logic 21. Furthermore, an I/O block containing a DAC 15 and an analog to digital converter (ADC) 17 allows sound card 13 to output analog signals to speakers or headphones and to receive analog input from microphones and other audio inputs through audio I/O lines 19. Because of the placement of sound card 13 in an expansion slot which has no outlet to the front panel of the PC housing, connectors to audio I/O lines 19 for microphones or headphones are in the back of the PC housing, which provides relatively inconvenient user access.

Still referring to Fig. 1, CD-ROM drive 27, located in the front panel of the PC housing, receives commands from CPU 22 through ISA bus 23 through an Integrated Drive Electronics (IDE) adapter interface circuit 25. This interface could also be a Small Computer

Systems Interface (SCSI). CD-ROM drive 27, being a self-contained unit, also has a DAC 29 for sound output processing which is a redundant component in this configuration, and increases overall cost, since sound card 13 already contains a DAC (element 15). A sheet metal casing 38 is provided, and shields CD-ROM drive 27 and its associated circuitry from the high noise levels that exist within a PC, unlike sound card 13 which is exposed to the high noise levels. For PC applications where a CD is used to store sound data and a sound card is used for sound processing, amplification, and output, an analog sound cable 31 must be used, at an added cost, to transport sound signals from CD-ROM drive 27 to sound card 13. Sound cable 31 is needed to shield the sound data from the noisy environment that exists inside a PC system and to bridge the physical distance separating sound card 13 from CD-ROM drive 27.

Fig. 2A is a block diagram showing an embodiment of the present invention wherein sound card electronics as conventionally implemented in a separate sound card are simply mounted on a common PCB with the drive electronics of a CD-ROM drive, and audio outlets for external speaker connection are provided. The inventors consider this to be a first step toward an integrated product, as readily available components are used.

In Fig. 2 A integrated unit 30 comprises a CD-ROM 34 which retrieves data from a CD-ROM disk and transfers the data via digital link 18 to CD-ROM drive electronics 16. Sound card electronics 24, including ADC 28 and DAC 26, is mounted on the same PCB as electronics 16, and a single trace 22 provides an analog link between electronics 16 and electronics 24. The sound card electronics provides output to speakers and analog input via I/O lines 28. The electronics are all implemented within a common shielding enclosure 32. Both electronics blocks 16 and 24 communicate with a host PC through an interface 14 and system bus 12. The interface may be either a proprietary interface or a standard IDE interface, as will be described more fully below. Fig. 2B is a block diagram showing a more fully integrated embodiment of the present invention with a CD-ROM drive 35, including a laser read head and tracking apparatus, CD-ROM electronics 37, and also sound card electronics 36 in a single integrated unit 33. CD-ROM drive 35, CD-ROM drive electronics 37, sound card electronics 36, including an I/O block having a DAC 41 and an ADC 43, are enclosed within a sheet metal casing 51. I/O lines 45 provide for analog input and output of sound signals. The entire package contained within sheet metal casing 51 is placed in the front panel of a PC housing, in the same position used for a conventional CD-ROM drive.

In the arrangement of Fig. 2B, since all of the components are in close proximity within sheet metal casing 51 , there may be substantially direct digital electronics from the CD-ROM drive and the sound card. This close association allows for sound data stored on a CD disk in CD-ROM drive 35 to be retrieved and more or less directly transferred to sound card electronics 36 without the use of an analog link, such as is conventional done with a sound cable. In addition, the close proximity of electronic components can also lead to further cost savings by implementing only one DAC, DAC 41, to serve both CD-ROM drive 35 and sound card electronics 39. In the arrangement shown by Fig. 2B, CD-ROM drive 35 is controlled by and transfers digital data to CD-ROM drive electronics 37 through I/O lines 53. In turn, CD-ROM drive electronics 37 passes digital data to and receives commands from sound card electronics 36 through I/O lines 55. The combination of data flow through I/O lines 53 and 55 gives CD-ROM 35 direct access to DAC 41 which renders a separate DAC for CD-ROM drive 35 unnecessary. Furthermore, with DAC 41, ADC 43 and sound I/O lines 45 also integrated into a single unit 33, the front panel of unit 33 includes connectors for headphones and microphones. This placement improves user access and usability by allowing the connectors to headphones and microphones to be in the front panel of a PC housing instead of the back.

A significant advantage of integration as in unit 33 derives from sheet metal casing 51 which shields sound card electronics 36 as well as CD-ROM drive electronics 37 from high ambient noise levels that exist in a PC system. This shielding improves output sound quality from sound card electronics 36 by lowering the overall SNR, leading to better overall sound quality from a PC system. This shielding was previously unavailable for sound card 13 in the conventional configuration in Fig. 1.

The blocks shown in Fig. 2B within shielding 51 are functional blocks, not necessarily indications of hardware separation or integration. In one alternative, blocks 37 and 36 are separate chips connected by digital pathway 55. In another preferred embodiment, all of digital electronics for retrieving, processing, amplifying, and converting sound data may be integrated in a single ASIC, including substantially all of the electronics in the integrated unit according to the invention. Communication between integrated unit 33 and the rest of a PC system is still accomplished through ISA bus 49 in this example. It will be apparent to those with skill in the art that in some systems, other bus structures may be used, such as Extended Industry Standard Architecture (EISA), high speed local buses, and even compressed buses.

In the conventional configuration of Fig. 1 , interface 25 is a conventional IDE adapter interface. In the configuration illustrated by Fig. 2, interface 47 may be either a standard IDE adapter or a proprietary controller, depending on either of two alternative solutions to communicating with the combination of CD-ROM and sound card electronics in unit 33.

In the conventional system of Fig. 1 , conventional control routines followed by CPU 22 provide communication with sound card 13 and CD-ROM drive 27 on alternate cycles of bus 23. Reading and writing to the CD-ROM is through the IDE controller 25, and to the sound card is through bus 25 to the expansion slot where the sound card is engaged. These are processes well known in the art, and involve digital addressing and data transfer techniques over the system bus. The destinations are controlled primarily be unique register addresses.

In the integration of the sound card electronics and the CD- ROM electronics, each must be addressed and accessed at the same physical location, preferably through a single connector. There are generally two ways this may be done. Either the registers for the CD- ROM and the sound card may be combined, and new control routines provided, or a hardware solution may be implemented by providing a new interface. The hardware solution is preferred, because it is transparent to conventional PC system operation.

In the first alternative, less preferred, no hardware changes to the standard IDE adapter interface need be made. In this alternative, integrated unit 33 is provided to be hardware compatible with current PC systems using a standard IDE interface. Unique commands are used to transmit sound data to and from a first-in-first-out (FIFO) memory device in the electronics section of the on-board sound card. Specifically, a proprietary software command set is provided to implement this specific embodiment without deviating from the IDE standard hardware.

Fig. 3 illustrates the specifics of this first alternative for PC compatibility. In Fig. 3, IDE adapter interface 55 does not deviate from the IDE standard, and is connected to communicate on ISA bus

53. Integrated unit 65 comprises a CD-ROM drive 67, CD-ROM drive electronics 57, and sound card electronics 59. In addition, sound card electronics 59 in Fig. 3 comprises a FIFO device 61 and an I/O block including DAC 63 and ADC 69. The new command set instructs CD-ROM drive electronics 57 to access CD-ROM drive 67 for sound data. This sound data is then transmitted to FIFO 61, which provides the sound data to DAC 63. FIFO 61 is needed to act as a buffer to store digital sound data so that sound can be output through DAC 63 in real time. FIFO 61 issues an interrupt when it needs more sound data. Alternatively, the new commands also instruct sound card electronics 59 to access sound data input from sound I/O lines 71 through I/O block ADC 69. This sound data is then transmitted to FIFO 61 for storage. Again, FIFO 61 is needed to act as a buffer since sound data input is in real time. In the second and preferred alternative, there are no software changes required to the conventional command set for a CD-ROM drive and sound card. In this alternative embodiment, an integrated unit having both a CD-ROM and a sound card is software compatible with current PC systems. To provide for the software compatibility, a unique adapter interface is provided to transparently emulate industry standard sound cards. The proprietary IDE adapter intercepts all accesses to sound card registers on the system bus and redirects them to the integrated unit. Also, the unique IDE adapter emulates the functionality of a DMA controller to ensure compatibility with existing software. Thus, after intercepting conventional sound card commands, the proprietary IDE adapter will automatically translate and decode them to provide the correct commands to the integrated unit.

Fig. 4 illustrates this second alternative embodiment for PC compatibility. In Fig 4, an integrated unit 73 having both a CD-ROM drive and a sound card is connected to a proprietary IDE adapter circuit 75 which communicates with ISA bus 77. IDE adapter circuit 75 creates commands for integrated unit 73 from the conventional sound card command set. In this way, compatibility with conventional PC software is maintained. This hardware solution is preferred by the inventors, because an enhanced IDE interface may be readily provided with an integrated CD-ROM/Sound Card unit according to the invention to provide compatibility with existing systems without the necessity of an altered command set for communicating with the new unit, which, in most cases, would require a new operating system or addition to an existing operating system.

Fig. 5 is an alternative diagram of the preferred system of Fig. 4. showing an integrated unit 73 with CD-ROM drive 67, a single chip electronics unit 81, and output speakers(s) 83. Selection and control is from the CPU (not shown) over bus 77 using proprietary interface controller 75. In a conventional IDE adapter interface, there is a select line for selecting a proprietary drive, generally termed primary and secondary, and address and data is routed to a primary or secondary drive accordingly. In the present situation, the primary may be a hard disk drive and the secondary integrate unit 73. The hardware solution essentially requires one more select lime (really an address line) to select the sound card part of the electronics or the CD part of the electronics in the integrated unit.

The selection is made by address location. Typically, a CD is addressed at four registers located at either 220 or 290, as shown in register indication 85 associated with the CD electronics. A sound card is addressed at four registers located at either 170 or 370, indicated at registers 87. In the proprietary controller, extra address line 89 is asserted to indicate CD mode, and not asserted to indicate sound card mode. With line 89 asserted, data is written to registers

85. and not asserted, to registers 87.

It will be apparent to one with skill in the art that there are many deviations in the embodiments described that might be made without departing from the spirit and scope of the invention. For example, as described elsewhere above, digital electronics, such as shown functionally in Fig. 3, can be highly integrated, with most integrated into a single integrated circuit (IC) resulting in lower parts count, lower cost and better coupling between the electronics, giving improved sound output performance. There are a variety of ways the electronics might be implemented, using techniques known in the art, and there are a variety of ways the necessary components might be physically integrated into a single unit.

Claims

What is claimed is:

1. An integrated CD-ROM sound processing unit, comprising: a CD-ROM drive, including a laser read head and tracking apparatus; drive electronics circuitry connected to the CD-ROM drive for operating the CD-ROM drive and for retrieving digital data from the laser read head; and sound electronics circuitry connected to the drive electronics; wherein the sound electronics circuitry and the drive electronics are enclosed in a metal shielding enclosure, and wherein the sound electronics circuitry receives sound data from the drive electronics circuitry, and provides analog sound signals to an external connector through a digital-to-analog converter (DAC).

2. An integrated CD-ROM sound processing unit as in claim 1 wherein the drive electronics circuitry and the sound electronics circuitry are implemented as separate integrated circuits, and the sound data is transferred from the drive electronics circuitry to the sound electronics circuitry as an analog signal.

3. An integrated CD-ROM sound processing unit as in claim 1 wherein the drive electronics circuitry and the sound electronics circuitry are implemented as separate integrated circuits, and the sound data is transferred from the drive electronics circuitry to the sound electronics circuitry as digital data over a digital link.

4. An integrated CD-ROM sound processing unit as in claim 1 further comprising a communication interface for connecting to a personal computer bus, wherein the communications interface is a standard Integrated Drive Electronics (IDE) interface.

5. An integrated CD-ROM sound processing unit as in claim 1 further comprising a communication interface for connecting to a personal computer bus, wherein the communication interface comprises select circuitry for selecting registers either in the drive electronics circuitry or in the sound processing circuitry.

6. An integrated CD-ROM sound processing unit as in claim 1 wherein the sound electronics circuitry comprises a first-in-first-out (FIFO) buffer for controlling flow of data between the rate that data is retrieved from a CD-ROM drive, and the rate the data is needed for real-time sound output.

7. An integrated CD-ROM sound processing unit as in claim 1 wherein the CD-ROM drive circuitry and the sound electronics circuitry are implemented as a single application-specific integrated circuit.

8. A computer system comprising: a CPU; a system bus connected to the CPU; a communication interface connected to the system bus; and a CD-ROM sound processing unit having a CD-ROM drive with a laser read head and tracking apparatus, drive electronics circuitry connected to the CD-ROM drive for operating the CD-ROM drive and retrieving digital data from the laser read head, and sound electronics circuitry connected to the drive electronics; wherein the sound electronics circuitry and the drive electronics are enclosed in a metal shielding enclosure, and wherein the sound electronics circuitry receives sound data from the drive electronics circuitry, and provides analog sound signals to an external connector through a digital-to-analog converter (DAC).

9. A computer system as in claim 8 wherein the drive electronics circuitry and the sound electronics circuitry are implemented as separate integrated circuits, and the sound data is transferred from the drive electronics circuitry to the sound electronics circuitry as an analog signal.

10. A computer system as in claim 8 wherein the drive electronics circuitry and the sound electronics circuitry are implemented as separate integrated circuits, and the sound data is transferred from the drive electronics circuitry to the sound electronics circuitry as digital data over a digital link.

1 1. A computer system as in claim wherein the communication interface is a standard Integrated Drive Electronics (IDE) interface, and the computer executes dedicated driver routines for communicating with the integrated CD-ROM sound processing unit.

12. A computer as in claim 8 wherein the communication interface for connecting to a personal computer bus selects registers either in the drive electronics circuitry or in the sound processing circuitry by driving a dedicated select line, and the computer executes the same driver routines used for a separate CD-ROM and sound card connected to the system bus. the integrated unit thus being software transparent.

13. A computer as in claim 8 wherein the sound electronics circuitry comprises a first-in-first-out (FIFO) buffer for controlling flow of data between the rate that data is retrieved from a CD-ROM drive, and the rate the data is needed for real-time sound output.

14. A computer as in claim 8 wherein the CD-ROM drive circuitry and the sound electronics circuitry are implemented as a single application-specific integrated circuit.

15. A method for providing controlled audio output from a CD-ROM drive comprising steps of:

(a) implementing electronic circuitry from a conventional sound card within the shielding enclosure of a CD-ROM drive;

(b) providing a computer bus interface for both the sound card electronic circuitry and CD-ROM drive electronic circuitry in the single enclosure; and

(c) coupling analog output of the CD-ROM drive circuitry to analog input of the sound card electronic circuitry.

16. The method of claim 15 further comprising a step for controlling both the CD-ROM drive circuitry and the sound card electronics circuitry by commands and data sent by a CPU connected to a system bus through the computer bus interface.

17. The method of claim 16 wherein the computer bus interface is an

Integrated Drive Electronics (IDE) interface, and the CPU executes dedicated driver routines for communicating with the sound card electronic circuitry and the CD-ROM drive circuitry.

18. The method of claim 16 wherein the computer executes the same driver routines used for a separate CD-ROM and sound card connected to the system bus, the integrated unit thus being software transparent, and a dedicated select line is used in the computer bus interface for selecting registers in either the sound card electronic circuitry or the CD-ROM drive circuitry.