Apparatus and method for audio computing

A computer for handling audio signals includes, within one box, programmable digital processing circuitry, read/write memory, digital-to-analog circuitry, one or more speakers, and an equalization element for altering the frequency response of signals applied to the speaker. The equalization element can be used to boost low frequency signals sent to the speaker if the speaker has poor low frequency response. Preferably the computer also has headphone and line-out jacks to which it supplies un-equalized audio outputs. The computer's internal speaker can be driven by a bridge mode amplifier, and, to save space, the speaker's electro-magnetic transducer can be placed in the concave recess formed by its speaker cones. The computer can have two speakers to play stereo. Preferably the computer receives analog inputs, such as from a built-in CD-ROM drive, a mike-in jack, and a line-in jack, and uses an analog-to-digital converter to digitizes these signals so they can be digitally manipulated by the computer. The computer preferably has a devices for selectively supplying the analog output from its digital-to-analog circuitry to either its internal speaker, headphone jack, or line-out jack. All of the computer's audio electronics can be placed on its motherboard, or they can be placed on a daughter board which plugs into the motherboard.

FIELD OF THE INVENTION 
The invention relates to apparatus and methods for use in computers which 
perform audio functions, such as, for example, the recording, processing, 
and playback of audio signal. 
BACKGROUND OF THE INVENTION 
There has been a recent trend to multimedia computing where the inputs of 
the computers are more than just text or still diagrams and drawings. 
Multimedia computing systems are often connected to microphones and audio 
speakers so they can record and playback sounds. Many have CD-ROM drives 
so they can play interactive multimedia works which include sounds, still 
pictures, animation, and moving video. Some of these CD-ROM drives can 
also play traditional audio CDs. 
One of the problems confronting the makers of computing systems is that of 
space. In the computer field smaller is usually better. Users generally do 
not want desk top computer that take up a large portion of their desk. And 
increasingly they are using even smaller computers, such as laptop and 
notebook computers. Unfortunately, the small speakers which fit in small 
computers tend to have a poor frequency response, particularly at the 
lower frequencies of the audible range. 
Another problems is that users often have many different potential uses for 
a computer's audio capabilities. Some want to record sounds from a 
microphone, others from a CD, others from a radio, and yet others from a 
tape or video recorder. On the output side, some want to play audio over 
speakers without having to wire up external speakers. Others might want to 
record the audio to a tape recorder, the audio track of a video recorder, 
or an external amplifier which drives external speakers. In the past many 
computers which have audio-in and audio-out capabilities cannot directly 
support all of these different types of devices. In addition, with most 
prior audio computers the user has to manually connect and disconnect 
different audio input and output devices to select which of them are to be 
used at any given time. 
SUMMARY OF THE INVENTION 
The present invention provides methods and apparatus for use in computers 
which handle audio signals. 
One aspect of the invention relates to a computer system which includes, 
within one box, programmable digital processing circuitry, read/write 
memory, digital-to-analog circuitry, one or more speakers, and an 
equalization element. The equalization element is for altering the 
frequency response of the signal applied to the speaker. In many 
embodiments of the invention, this equalization element boosts the low end 
of the audible frequency range relative to the mid-range to compensate for 
the fact that most small, thin speakers of the type which would best fit 
into most such computers reproduce low frequencies more poorly than 
mid-range frequencies. 
In a preferred embodiment the computer also has headphone and line-out 
jacks to which it supplies un-equalized audio outputs. Preferably the 
computer's internal speaker will be driven by a bridge mode amplifier to 
allow it to have a maximum voltage given the power voltages available on 
the computer. In many embodiments, the computer has two speakers and can 
play back stereo signals. It is preferred that the computer can receive 
analog inputs, such as from a built-in CD-ROM drive, a mike-in jack, and a 
line-in jack, and that the computer have analog-to-digital conversion 
circuitry for converting such analog signals to a digital form which can 
be read and processed by the computer. In some embodiments, each of the 
computer's built-in speakers has its electro-magnetic transducer placed in 
the recess formed in front of its concave speaker cone to save space. 
According to another aspect of the invention, a computer has 
analog-to-digital circuitry which receives signals from a line-in jack and 
a mike-in jack. This computer also has devices for selectively supplying 
the analog output of its digital-to-analog converter to an internal 
speaker, a headphone jack, or a line-out jack. This gives the computer the 
ability to function as a flexible audio computer capable of receiving and 
outputting from and to most audio devices. It also makes it easy for the 
user to leave the system's built in speaker hooked up, its headphone 
output connected to headphones, and its line-out jack connected to an 
external electronic device, without the need to connect or disconnect such 
devices to determine which of them should receive audio output. 
In one preferred embodiment of the invention, all of the computer's audio 
electronic circuitry is on the computer's motherboard. This makes it 
possible for the system to provide such audio electronics at a lower cost. 
In another embodiments all of the audio electronics are on a daughter 
board which plugs into the motherboard, allowing the system to be sold 
without audio electronics for those who have no use for them.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1, a computer system 30 is shown which embodies the 
present invention. The computer shown is a desktop computer roughly 
similar to a SCStation 5 workstation computer manufactured by Sun 
Microsystems, Inc. In other embodiments of the invention other types of 
computers could be used, including so-called, IBM PC compatible computers. 
The computer system 30 includes an enclosure box 32. This box includes a 
metal chassis 29 (shown in simplified form in FIG. 1) which supports the 
components shown in FIG. 1 and a plastic enclosure box 31 (shown in 
cross-section in FIG. 1) which goes over that chassis. Inside the 
enclosure 32 is mounted a power supply 33 which converts standard 
alternating current power into the various direct current voltages needed 
by the computer's electronics. 
Also inside the enclosure 32 is a motherboard 34 on which most of the 
computer's electronic components are mounted. These components includes a 
central processing unit, or CPU, 36 which communicates over a memory bus 
38 with DRAM memory 40. The CPU can read from or write to this memory, and 
use it to store data or programs for controlling the operation of the CPU. 
In the preferred embodiment the CPU is a SC microprocessor with a high 
speed memory cache built in. 
The CPU communicates with a plurality of other devices through a separate 
bus 42. The bus 42 is an SBus, a well known type of bus designed by Sun 
Microsystems, Inc. The other devices connected to the SBus include a 
serial I/O controller 44, a parallel and SCSI controller 46, and a special 
I/O controller 48, all of which are mounted on the mother board. The 
special I/O controller 48 is connected, among other things, to the 
computer's audio electronics 49, which are also mounted on the 
motherboard. 
As is well known in the computing arts, the CPU 36 reads instructions from 
memory 40 and executes them. These instructions cause the CPU to read and 
write information from and to portions of the memory over the memory bus 
38 and from and to other devices connected to the SBus 42. The serial I/O 
controller 44 receives inputs from a keyboard 54 and a mouse 56 and relays 
them to the CPU. It also controls, and transfers data to and from, a 
floppy drive 58. The parallel I/O controller is connected to a parallel 
port 60. It also contains a SCSI controller which controls, and transfers 
data to and from, SCSI devices which are connected to it. These include a 
CD-ROM drive 62 and a hard disk 64, both of which are mounted in the 
chassis of the computer's enclosure box 32. The SCSI controller is also 
connected to a connector 66 mounted on the motherboard at the back of the 
computer, where it can be accessed through a correspondingly shaped hole 
in the enclosure 32. 
A graphics controller daughter card 50 is plugged into a multicontact 
connector 52, which connects it electronically to the SBus on the 
motherboard. The controller contains a connector 68 which also can be 
accessed through a hole in the back of the computer's enclosure. The 
graphics controller receives data representing screen images from the CPU 
and converts them into the signals necessary to generate corresponding 
images on the screen of the monitor 70. 
FIG. 2 provides a more detailed diagram of the motherboard's audio 
electronics 49. These electronics are shown encircled in dotted-lines in 
that figure. They receive digital commands and data from, and send digital 
data to, the CPU 36 through the special I/O controller 48. Digital signals 
from the special I/O controller are supplied to a CODEC chip 77, which, in 
the embodiment shown, is a CS 4231 CODEC manufactured by Crystal 
Semiconductor, Inc., of Austin, Tex. 
The CODEC chip 77 includes a stereo analog-to-digital converter within it. 
This converter receives as an input two stereo analog signals, and 
produces as an output two corresponding digital values representing, 
respectively, the magnitudes of the voltages of the two analog signals. It 
does this many thousands of times a second to produce a succession of 
digital values representing each of the analog signals over time. The 
computer's audio electronics include three analog stereo input connectors: 
a CD connector 78, a mike-in jack 80, and a line-in jack 82. Each of these 
connectors 78, 80, and 82 has a stereo analog signal path, 84, 86, and 88, 
respectively, connecting it to the CODEC. The CODEC chip includes 
multiplexing electronics for selectively switching the stereo signal on 
each such path to the input of the stereo analog-to-digital converter in 
response to digital commands supplied to the CODEC from the CPU through 
the special I/O controller 48. 
The mike-in connector 80 is designed to receive relatively low voltage 
stereo analog inputs from stereo microphones, such as the stereo 
microphones 102, shown in FIG. 1. The line-in connector 82 is designed to 
receive higher voltage stereo signals from the outputs of other audio 
electronic equipment, such as the amplifier/tuner/tape player 104 shown in 
FIG. 1. The CD connector 78 is designed to receive analog stereo inputs 
from the CD-ROM drive 62 shown in FIG. 1. This CD-ROM drive can play 
CD-ROM data diskettes, supplying data read from such CD-ROM diskettes in 
digital form to the SCSI port on the parallel I/O controller 46 shown in 
FIG. 1. It can also play standard audio CDs, converting the digital 
information stored on such CD's into an analog stereo signal. It is this 
stereo analog signal which is supplied to the connector 78. 
Each of the analog input signal paths 84, 86, and 88 is shown in a highly 
simplified form in FIG. 2. Each couples the left and right channel of its 
associated stereo input to an analog input of the CODEC chip through at 
least one pair of DC filtering capacitors 90, which filter out direct 
currents and very low frequencies from the signal supplied by its 
associated signal path to the CODEC chip 77. 
The line-in signal path 88 connects the left and right channels received 
from the line-in jack to associated DC filtering capacitors 90 through 
voltage dividers. Each such voltage divider is formed of two equal 
resistors 87, one between the capacitor and the line-in jack, and one 
between the capacitor and ground. These voltage dividers cut in half the 
voltage of the signals supplied to the CODEC's LINL and LINR inputs. This 
decreases the chance that those signals will exceed the CODEC's input 
voltage limit, which would cause them to be audibly distorted. 
The mike-in signal path 86 connects each of the stereo channels received 
from the mike-in jack to the input of an amplifier 92 through a DC 
filtering capacitors 90. Each of the amplifiers has a 40X voltage gain to 
boost the relatively small voltage signals produced by most microphones to 
signals having a voltage appropriate for use with the CODEC's 
analog-to-digital converter. Since each of the 40X amplifiers has an 
output centered about 2.5 volts, that output is connected to the MICL or 
MICR input of the CODEC chip through a capacitor 94, which removes the 
outputs 2.5 volt DC bias. 
The CD signal path 84 starts with the connector 78, which has three 
contacts 96, 98, and 100, connected to a three wire cable (not shown in 
FIG. 2) from the CD-ROM drive 62. The contacts 96 and 98 receive the left 
and right stereo signals from the CD-ROM drive, respectively. Each of 
these signals is coupled through a DC filtering capacitor 90 to one input 
of an associated 1X amplifier 93. The connector 100 receives the ground 
voltage from the CD-ROM drive. It is coupled, through a DC filtering 
capacitor 90, to the other input of each of the two amplifiers 93. Each of 
the amplifiers 93 is connected to the local ground voltage 79 in the 
vicinity of the CODEC, and each produces as an output voltage variations 
equal to the variations of the voltage difference between its two input, 
defined relative to the CODEC's local ground voltage 79. The output of 
each of the amplifiers 93 is passed through a capacitor 94 to remove the 
2.5 volt DC bias which results because the output of each such amplifier 
is centered about 2.5 volts. 
The 1X amplifiers 93 are used in the CD signal path to ensure that the 
stereo signal it supplies to the CODEC has the same voltages relative to 
the CODEC's local ground 79 as the stereo signal generated by the CD-ROM 
drive had relative to that drive's local ground 63. This is necessary 
because the CODEC's analog-to-digital converter measures the voltages of 
its input signals relative to the CODEC's local ground 79. But the local 
ground 79 of the CODEC varies from that of the CD-ROM drive. This is 
because the CD-ROM drive is located at the other end of the computer from 
the CODEC and its local ground is connected to that of the CODEC's by 
multiple circuit paths formed by the computer's metal chassis 29. Both low 
and high frequency ground currents can be induced into these circuit paths 
by the operation of the computer's electronics, causing differences 
between the ground voltages at the CD-ROM drive and the CODEC. It is these 
differences which are filtered out by the amplifiers 93. 
The CODEC chip 77 also includes within it a stereo digital-to-analog 
converter. This D/A converter receives two successions of digital values 
supplied from the CPU 36 through the Special I/O controller 48. These 
successive values represents the amplitudes of the audio signal in each of 
two stereo channels at successive periods times. It converts these 
successions of digital values into two analog signals having corresponding 
variations in voltage amplitude. The left channel of the resulting stereo 
analog signal is output by the CODEC chip on the LOUTL line 106. The right 
channel of that signal is output on the LOUTR line 108. The ground output 
for this stereo signal is connected to the local ground on the motherboard 
via the ground connector 79. 
The stereo signal on the LOUTL and LOUTR lines is connected through three 
pairs of analog switches 110, 112, and 114 to a speaker stereo signal path 
116, a headphone stereo signal path 118, and a line-out stereo signal path 
120, respectively. These analog switches individually connect or 
disconnect the stereo signal produced at LOUTL and LOUTR from the signal 
paths 116, 118, and 120. 
The analog switches 112, which connect or disconnect the headphone signal 
path 118 to LOUTL and LOUTR, are opened and closed by the first external 
control line of the CODEC chip, EXCTL1 122. The analog switches 114, which 
selectively connect or disconnect the line-out signal path 120 to LOUTL 
and LOUTR, are controlled by the second external control line of the CODEC 
chip, EXCTL2 124. The binary states of the EXCTL1 and EXCTL2 outputs are 
controlled by digital control signals the CPU sends the CODEC through the 
special I/O controller 48. 
Since the CODEC chip only has two external control lines, EXCTL1 and 
EXCTL2, the two analog switches 110, which selectively connect the speaker 
signal path 116 to LOUTL and LOUTR, are controlled by an output 126 from 
the special I/O controller 48, which is set high or low by digital signals 
from the CPU. 
Each of the two channels of the stereo analog speaker signal path 116 
includes a low pass filter 128 and a high pass filter 130, a bridge mode 
drive amplifier 132, and wires 72 which connect the output of the drive 
amplifier to the channel's associated speaker 74. These speakers are 
mounted on the front of the computer's enclosure 32, as is shown in FIG. 
1, behind a series of holes 76 provided to let the sound they produce more 
easily be heard outside the computer. 
The low and high pass filters 128 and 130 in each channel of the speaker 
signal path function as equalization elements. They alter the frequency 
spectrum of the signals supplied to the channel's associated speaker 72 to 
compensate for the uneven frequency response of that speaker. This is done 
to make the sound produced by the speakers more pleasing. To save money, 
space, and weight, the speakers 72 are relatively small, inexpensive, 
speakers. As a result they do not reproduce sounds at the low end of the 
audible spectrum, frequencies in the range from sixty to several hundred 
hertz, nearly as loudly as they do frequencies in the mid-range of the 
audible spectrum centered around two to five thousand hertz. 
To compensate for this lack, and to improve the sound of the system, the 
low and high pass amplifiers 128 and 130 alter the frequency spectrum of 
the analog signals supplied to the left and right speakers as indicated in 
the curve 134 shown in FIG. 3. In this graph the horizontal axis 
represents frequency of the signal in a logarithmic scale. The vertical 
axis represents in decibels the ratio of the amplitude of the signal 
supplied to the speakers to the amplitude of the signal on LOUTL or LOUTR. 
As is indicated in FIG. 3, the low pass filter 128 boosts the low frequency 
end of the spectrum, that between sixty and one thousand hertz. This boost 
is as large as six decibels, or approximately four times the power, at 
approximately one hundred hertz. The high pass amplifier 130 increases the 
amplitude of frequencies near the high end of the audible range to 
compensate for the tendency of the low pass filter to decrease their 
amplitude, causing those high frequencies to have almost the same volume 
as if there were no equalization at all. Together, the low and high pass 
filters cause frequencies in the middle of the audible range, from 
approximately one thousand to ten thousand hertz, to have slightly less 
amplitude than they otherwise would. This is to compensate for the fact 
that the speakers 74 have their best frequency response in this middle 
range and would tend to make such frequencies too loud, giving a tinny 
sound, were it not for such equalization. 
The equalized analog signal produced by the combination of the low and high 
pass filters 128 and 130 in each channel of the speaker signal path is 
supplied to the input of a bridge mode amplifier 132. The bridge mode 
amplifier amplifies this signal sufficiently to drive the channel's 
associated speaker 74. Each bridge mode amplifier consists of two ten volt 
amplifiers 136 and 138, each of which has a maximum output voltage swing 
between ground and plus ten volts. In each such amplifier approximately 
five volts represents an audio signal of zero amplitude. The bridge mode 
amplifier effectively doubles the voltage across each speaker by causing 
one of its two amplifiers to have an output above five volts proportional 
to the audio signal's amplitude and the other to have an output below five 
volts proportional to that amplitude. Thus, the difference between the 
outputs of these two amplifiers is twice as great as the difference 
between a single ten volt amplifier's output. 
The outputs of the bridge mode amplifiers 136 and 138 of each channel are 
supplied to connectors 140 on the motherboard. The wires 72 which are 
attached to the speakers 74 are plugged in to these connectors. 
The headphone stereo signal path 118 is selectively connectable to LOUTL 
and LOUTR through the analog switches 112 at one end. It is connected to a 
stereo output jack 142 at the other end. The jack can be used to connect 
this signal path to a pair of stereo headphones, such as the headphones 
144 shown in FIG. 1. The headphone signal path includes an amplifier 146 
on each of its two channels, the output of which is capacitively coupled 
to an associated one of the left and right signal contacts of the output 
jack 142. The amplifiers 146 have a 1X voltage gain, that is, their output 
has the same voltage variation as their input. But they are capable of 
driving much larger currents than the LOUTL and LOUTR outputs of the CODEC 
chip 77, as is necessary to drive the voltages produced at those outputs 
across the relatively low impedances commonly found in headphones. The 
capacitors 148 help to protect the headphone signal path from direct 
currents and remove any DC bias produced by the output of the amplifiers 
146. 
The line-out signal path 120 is selectively connectable at one end to the 
LOUTL and LOUTR lines through the analog switches 114. At the other end it 
is connected to a line-out jack 150. It is essentially similar to the 
headphone signal path 118 except that its amplifier's 147 are not designed 
to drive as much current as the amplifiers 146 in the headphone signal 
path. This is because the line-out jack is designed to supply signals to 
inputs of electronic devices, such as the amplifier/tuner/tape player 104 
shown in FIG. 1, which normally have a much higher input impedance than 
headphones. 
Those skilled in audio computing will appreciate that the audio electronics 
shown in FIGS. 1 and 2 enable stereo analog audio signals to be received 
either from microphones through the mike-in jack 80, from the output of an 
external electronic device through the line-in jack 82, or from the 
computer's CD-ROM drive. Under the control of digital signals sent from 
the CPU to the CODEC chip, the CODEC can select which of these analog 
inputs to convert into corresponding digital signals. These digital 
signals can be read by the CPU through the special I/O controller 48 and 
stored in the computer's memory 40. From there the CPU can cause these 
digital signals to be written by the CPU onto floppy disk, hard disk, or 
any other mass storage device connected to the computer's SCSI bus, such 
as a read-write optical disk. 
Similarly the device can output audio by having the CPU read digital stereo 
signals from memory or from a mass storage device and write them through 
the special I/O controller 48 to the digital-to-analog converter on the 
CODEC chip 77. This causes a corresponding stereo signal to be produced at 
the chip's outputs LOUTL and LOUTR. The CPU can select which combination 
of the analog signal paths, that leading to the speakers 74, the headphone 
jack 142, or the line-out jack 150 will receive this stereo signal. The 
CPU's ability to choose which output signal path will receive the CODEC's 
analog output allows the user of the computer to selectively turn on and 
off its audio outputs under software control without the need to 
physically plug or unplug output devices. The fact that the computer's 
memory 40 can be loaded with different programs, which can control and use 
the computer's audio features in different ways, further increases the 
computers's flexibility as an audio device. 
FIG. 4 shows an inverted speaker 74 used with the embodiment of the 
invention shown in FIG. 1. This speaker has an electro-mechanical 
transducer 160 which is comprised of two portions. The first portion is a 
permanent magnet 162 in the shape of a cylinder mounted in the center of 
the speaker's front frame 164. The transducer's second portion includes a 
hollow cylindrical structure 166 made of a materials such as paper or 
plastic on which a wire coil 168 is wrapped. This coil is connected to the 
wires 72 connected to the output of the speaker's associated bridge mode 
amplifier 132. The coil and the hollow cylinder upon which it is wrapped 
are designed to slide in and out over the end of the permanent magnet 162 
in response to variations in the electromagnetic field generated by that 
coil which variously attract or repel the permanent magnet. 
The hollow cylinder 166 is attached near its end which faces away from the 
permanent magnet to the center of the speaker cone 170. The speaker cone 
is positioned so that its concave surface 172 faces the permanent magnet 
162 and the front frame 164 upon which that magnet is mounted. Since the 
cone's front surface 172 is concave, its center, where the hollow cylinder 
166 of the electromagnetic transducer is attached, is recessed relative to 
the cone's outer edges 174. These outer edges are attached to a circular 
flexible rubber strip 176, called a surround, which, in turn, is attached 
to the speaker's frame. 
The front frame 164 of the speaker contains large openings through which 
sound waves generated by the motion of the speaker cone can travel. It 
also includes a fine screen to cover those openings to keep dust off of 
the front of the speaker cone and the electromagnetic transducer. 
The back of the speaker is formed of a circular piece of sheet material 
178, called a spider, which has circular folds 180. The spider is 
connected at its center to the hollow cylinder 166. It functions to help 
center the hollow cylinder 166 and the coil 168 around the axis of the 
cylindrical permanent magnet 162 and to help keep dust off the back of the 
speaker cone. 
The speaker 74 is different from conventional speakers because it places 
the permanent magnet 162 and the coil 168 of its electromechanical 
transducer in front of its speaker cone, rather than behind it. By placing 
this transducer in the recess formed by the speaker cone's concave 
surface, the speaker saves space, enabling a speaker with a given cone and 
cone travel to be thinner. This is particularly important in computers 
where size is at a premium. 
FIG. 5 shows a computer system 30A which is identical to the system 30 
shown in FIG. 1, except for the following differences illustrated in FIGS. 
5 and 6. 
First, it only has one speaker, a speaker 74A, instead of two, and it is a 
conventional speaker, that is, one with its electromagnetic transducer 
behind its speaker cone, rather than one, like that shown in FIG. 4, with 
its transducer in front of its cone. 
Second, its audio electronics 49A are on a daughter board 184, rather than 
being on the system's motherboard 34A. The electronics on this daughter 
board are connected to those on the motherboard through a connector. This 
connector has two mating portions, a portion 186A which is part of the 
motherboard and a portion 186B which is part of the daughter board. The 
connectors 186A and 186B connects the CODEC 77 on the daughter board to 
the computer's special I/O controller 48A which is on the motherboard. It 
also connects the output of the bridge mode amplifier 132 in the daughter 
board's single speaker signal path 116A to a connector on the motherboard 
to which the wires 72A to the speaker 74A are connected. In addition, it 
connects power lines on the daughter board to those in the motherboard 
(neither of which are shown in the drawings). 
Third, since the daughter board's speaker signal path 116A is monaural 
instead of stereo, it is connected to the MONO.sub.-- OUT output of the 
CODEC chip 77. This output is produced by the CODEC chip through mixing 
the two analog outputs which the chip's stereo digital-to-analog converter 
supplies to LOUTL and LOUTR. The CODEC chip includes within it an analog 
switch on its MOUT.sub.-- OUT output which is switched on and off by 
digital commands supplied to the CODEC chip from the CPU through the 
special I/O controller 48A. Thus, there is no need for an analog switch 
110 external to the CODEC chip or a special control line 126 to control 
such an external analog switch, as is required in the embodiment of the 
invention shown in FIG. 2. 
Finally, the mike-in connector 80, the line-in connector 82, the headphone 
out connector 142, and the line-out connector 150 are all mounted at the 
rear of the audio electronics card 184, position so that they can stick 
through an opening in the rear portion of the computer's enclosure when 
the daughter card's connector 186B is connected into the motherboard's 
connector 186A. 
Having the computer's audio electronics on a separate card makes it 
possible to sell the computer 30A either with or without those 
electronics. In the preferred embodiment, the computer 30A is sold with 
the speaker 74A even if the audio card 184 is not included. This enables a 
user to add the audio card at a later time without the need to also 
install a speaker into the computer. 
In an alternate embodiment of the invention which is not shown in the 
figures, the computer's audio electronics are placed on a daughter card 
184 as shown in FIGS. 5 and 6. But in this alternate embodiment an SBus 
connectors is positioned parallel on the motherboard to the audio daughter 
card's connectors 186A and 186B. The SBus connector is taller than the 
audio card's connector, and it is position so that when an SBus card is 
connected to it, the SBus card will be parallel to, and above, the audio 
card. The card plugged into the SBus connector has a separate openings in 
the back of the computer, above that for the audio card, for supporting 
its other end and for allowing users easy access to input and output 
connectors located on that other end. 
It should be understood that the forgoing descriptions and drawings are 
given merely to explain and illustrate the invention and that the 
invention is not to be limited thereto, except in so far as the 
interpretation of the appended claims are so limited. Those skilled in the 
art who have the disclosure before them will be able to make modifications 
and variations therein without departing from the scope of the invention. 
For example, it should be understood that in other embodiments of the 
invention the computers used could be other than desktop computers. For 
example, they could be laptop or notebook computers. Similarly other 
embodiments of the invention could be made with different types of 
processors, such as concurrent processors or CISC processors. 
Other embodiments of the invention might also use CODEC chips with 
different sets of features, or might even use analog-to-digital and 
digital-to analog converters which are separate components or which are 
integrated onto a processor or digital signal processor chip. 
Similarly, it should be understood that in other embodiments the output of 
the CD-ROM produced when playing standard audio CDs could be a digital 
output supplied to a digital I/O controller, such as the parallel I/O 
controller 46 shown in FIG. 1, rather than the analog output supplied 
directly to the computer's audio electronics, as described above. 
It should further be understood that in other embodiments the equalization 
element which compensates for the limited frequency response of the 
computer's speaker could be other than the combination of a low and high 
pass filter in the speaker signal path. For example, in some systems such 
equalization could be performed digitally by the CPU itself, or by a 
digital signal processing chip under the control of the CPU. 
Accordingly, the invention is not to be limited to the specific embodiments 
illustrated and described, and the true scope and spirit of the invention 
are to be determined by reference to the following claims.