Today, sound is an inherent part of the PC. There are a variety of components common to virtually all PC sound system: a sound card, an amplifier, speakers, shielding, and drivers and specialized software. The sound card, also known as an audio adapter, is an expansion card that adds the ability to record and play back sound from internal or external sources. The sound card integrates all of the elements required to capture and reproduce sound. The elements of the sound card are the input, outputs, and signal processors, which are the 4 digital to audio converters (DACs) and analog to digital converters (ADCs) required to convert sound into or from digital data.
The sound card typically includes jacks (connectors to accept sound inputs from a microphone or another sound source, such as a CD player or the like, and output jacks for speakers, amplifiers, or other sound recording equipment. Most sound cards are typically ISA or PCI adapter cards.However, the recent trend is to directly mount a sound chip on the motherboard, which eliminates the need for an audio adapter card.
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| Sound Card |
The components included on the sound card to convert sound into and out of digital data formats are as follows:
- Digital to analog converter (DAC): The DAC converts digital audio data from a hard drive or another storage medium into analog sound (normal everyday sound waves) that can be played back on the speakers or a set of headphones.
- Analog to digital converter (ADC): An ADC converts analog sound waves, such as a voice or a musical instrument, into digital data so it can be stored, edited, and transmitted.
- Analog inputs: Sound cards have two separate analog sound inputs: line level and microphone-level. Line-level inputs accept sound signals from electronic sources such as CD players or tape decks or signals that are directly input from a musical instrument, such as an electronic piano or a synthesizer. There are two separate inputs because microphones produce signals with a much lower voltage level than those from line-level sources. Mic-level inputs are generated from a stand-alone microphone or an amplified electric guitar plugged into the mic-level input. Line-level inputs are designed to handle the higher voltage signal produced by amplified electronic devices. The most common connector on analog inputs is the standard 1/8-inch phone jack that is just like those on the earphones of your portable CD or tape player. professional or more specialized sound cards may include left and right stereo RCA jacks, which are 1/4-inch phone jacks like the ones used to connect earphones to your home stereo components. The RCA jack, named for the early sound pioneering company, is the standard for professional studio equipment. Other important features and components found on most PC sound cards include:
- Analog outputs: Most sound cards have two analog output jacks. One, which is usually identified as Phones Out or Speaker Out, (or is marked with a picture to that effect) is powered by a small amplifier on the sound card that is capable of producing the sound for headphones or passive speakers. The other jack, usually labeled as the Line Out jack, produces a line-level signal that can be used as an input to a home-stereo receiver, for example. Like the analog input jacks, 1/8-inch phone jacks are the most common, but higher-end cards use RCA (1/4-inch) phone jacks.
- Digital I/O (input/output): This type of connector on a sound card makes it possible to accept input or send output directly to a digital device, such as a MiniDice or digital audio tape (DAT), without ever converting the data from digital to analog. This eliminates the need for the data to pass through either a DAC or an ADC, which always has the potential to degrade or distort the sound signal. It won't mean much to anyone except a sound engineer, but the most common digital interfaces used on sound cards are S/P-DIF (Sony/ Philips Digital Interface) and AES/EBU (Audio Engineering Society/European Broadcasting Union).
- Game/MIDI port: This connector is commonly used for game controllers such as joysticks or game pads. However, with a special type of cable, this port can be connected to any external MIDI (Musical Instrument Digital interface) device to send and receive MIDI data.
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| midi/game port |
- Digital Signal Processor (DSP): Once found only on expensive high-end sound cards, the DSP chip serves only one purpose: to relieve the PC's CPU of the burden for processing audio data. As DSP chips become less expensive and are included in more and more devices, they are now finding their way onto less expensive sound cards. DSP chips are the fastest growing segment of the semiconductor industry as more demand is being generated for sound reproduction in smaller and smaller devices. Among the tasks performed by the DSP chip on a sound card are re-sampling (changing the bit depth and sample rate of audio data) and adding digital effects such as reverb and echo to an audio piece.
- Synthesizer: Unlike digital data that is sent through the DAC to be converted to sound, MIDI signals tell the sound card which sounds to make, at what frequency, and for how long. In order to play back MIDI sounds, the sound card must be able to generate these sounds using a synthesizer chip. Through MIDI signals, an external MIDI device can control the sound card's synthesizer chip. Synnthesizer chips vary widely in capabilities and sound quality, but many newer sound card now incorporate Wavetable that produces a higher quality sound by using digital samples of actual instruments in place of other synthesized sounds.
ISA Sound Cards
Like other ISA expansion cards, ISA sound cards usually require some manual configuration to set the system resource assignments such as I/O port address, DMA, and IRQ for the card. These values are typically set with a series of jumper blocks on the card. Some cards require a combination of jumper settings and some entries in the AUTOEXEC.BAT and CONFIG.SYS files located in the root directory of the hard disk drive. The documentation and installation instructions that come with the card will specify the exact entries needed.
ISA sound cards can be especially complicated to configure because they often use a separate set of values for different functions. For example, there are sound cards that require a separate port address, DMA, and IRQ for general use, another set of values for sound Blaster emulation, and a third set of values for MPU-401 emulation. That's nine resources to configure for a single expansion card! As you can see, there is no universal set of steps for configuring an ISA sound card. The only way to know exactly what values need to be assigned and how to assign them is to refer to the manufacturer's documentation. If the manual for the card is unavailable, many sound card manufacturers publish installation guides on their Web sites.
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| ISA sound card |
PCI Sound Cards
Many of the difficulties associated with configuring an ISA sound card are eliminated with PCI sound cards. Although there are still a number of resources that need to be assigned, this is typically accomplished by the Plug-and-Play BIOS in conjunction with an operating system that supports Plug and play, like Windows 95/98/2000. In most of these cases, certain system resources, such as IRQ and DMA, cannot be assigned manually.
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| PCI Sound Card |
A few conditions must be met before a PCI card can be installed:
- There must be an available PCI slot.
- Many older motherboards use an earlier revision of the PCI BIOS that may not be compatible with newer sound cards. Check with the motherboard manufacturer if you have an older PCI motherboard and are not certain that the PCI BIOS revision may be less than version 2.1.
- Motherboard manufacturers commonly develop system BIOS updates after the motherboard is released. Sometimes these updates are designed to address issues such as Plug-and-Play device enumeration that can affect whether or not a card is successfully installed. Check with your motherboard manufacturer to see if there are any critical BIOS updates available. Always use caution when upgrading a system BIOS.
Installing a Sound Card
- Power down the system before opening the case. On ATX systems you may have to press and hold the power button for several seconds before it turns off. Check that there are no lights illuminated on the front of the case and no fans spinning.
- Always use and anti-static wrist strap when working inside the PC to prevent damage from ESD (electrostatic-discharge).
- Avoid using magnetized screwdrivers while working inside the PC.
- Do not contact the surface of the printed circuit board (PCB) on the motherboard or other adapter cards with your tools, or you may damage the boards.
- Before closing the case, check to see that all expansion cards, RAM modules, and cable connections are still firmly in place.
Amplifier
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| Amplifier |
Speakers
Like all speakers, PC speakers are categorized into two general groups: passive and active passive speakers do not include an amplifier; active speakers do. A passive speaker, which is what most standard PC speakers are, receives a signal that has been amplified enough to generate motion in the speaker's diaphragm and proface sound. An active speaker includes a built-in amplifier and typically does not require external amplifiers. An active speaker can accept low-level (line-level) signals. Nearly all PC speakers are passive speakers, with the exception of subwoorers. subwoofers. Subwoofers are speakers that generate only very low frequency sounds, like bass tones. A subwoofers are speakers that amplifier, which makes it an active speaker. The benefit of having a subwoofer on your system is that it will handle all of the low bass sounds, leaving the system's passive speakers and the amplifiers driving them to handle higher-level sounds, which are much easier to reproduce.
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| Speakers |
One major disadvantage of USB speakers is that there are no input jacks that can be used to connect external or internal devices like a CD-ROM or DVD player.
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