Everything You Need to Know About Your Computer Sound Adapter (Card)

Your computer's ability to produce sound - however good or bad - is entirely dependent on a piece of hardware, sometimes available as a separately installed adapter called the sound card or sound adapter, and sometimes integrated as an additional set of chips on your motherboard. But that sound hardware, regardless of whether it's a separate adapter or integrator, performs an incredible number of jobs.

Major Functions of the Sound Adapter

From a user's perspective, there are four major responsibilities borne by the sound adapter:

- To record audio from external devices (example: microphone or from a taped source) and then save this in a supported audio media format
- To playback pre-recorded sound
- To process existing sounds
- To provide sound synthesis capability

Components of Recent Sound Adapters

As you already know, today's typical sound adapter isn't really just one device that exists to push sound out from a signal of information generated from the CPU. Instead, it's a collection of devices, plus connections for attaching yet more devices, that bring sound into the adapter and convert it into a signal understandable by the PC, transmit sound out through the speakers or headphones, or work with musical or other add-on devices such as MIDI keyboards, microphones, and gaming hardware.

Let's look at some of the components here, and then examine them more closely by taking each part individually.

The components typically seen are:

-Digital Signal Processor (DSP) or more simplified on-board processor
-Digital-to-Analog Converter (DAC)
-Analog-to-Digital Converter (ADC)
-Sample rate generator
-Amplifier (optional, a legacy from the days on non-amplified speakers requiring the sound adapter to have an amplifier to push and magnify sound)
-Memory (either ROM or Flash)
- Musical Instrument Digital Interface (MIDI) connection
- Jacks for various connections (speakers, line in/line out, microphone, sometimes headphones)
- Game port

More about the core components - DSP, converters, sample rate generator, and MIDI connectivity - follows.

Digital Signal Processor (DSP)

Today's digital signal processor (DSP) is at the core of the technology that has helped sound adapters mature into far more sophisticated ranges and delivery.

In many respects, the DSP behaves like the sound adapter's CPU but dedicated to and optimized for audio processing, handling computations and relieving the CPU of much of the demands normally placed upon it by sound functions. Plus the DSP is responsible for making any determined modifications to the audio, such as:

-Chorus (special doubling effect to seem like two or more instruments are being played at once)
-delay
-distortion (purposeful)
-echo
-reverb (for reverberation, or a representation of the effect you get playing music in a concert hall)

The DSP also acts as overseer of the process of both sending and receiving signals handled directly by the DAC and the ADC, as well as the compressor of the digital signal. It is also an essential component in speech-to-text processing.
Specific jobs for the DSP depend on what mode is being used: 2D or 3D. For 2D mode, the DSP handles the effects like chorus and echo mentioned above. For 3D mode, the DSP is highly involved with 3D-positional audio, such as you find with DirectSound3D or other standards like Creative Labs EAX or Aureal's A3D, that would usually need the power of a full CPU to render. In this manner, DSP is important to the hardware acceleration of the audio component of the multimedia subsystem on the PC allowing for different numbers of sound streams depending on the type of support offered in the sound adapter itself.

Like the video adapter and its graphics processor, the digital signal processor on a sound adapter is usually the core identified component and the one considered most important for the overall quality of the adapter. A DSP or more simple processor may not be designed specifically by the manufacturer of the card, but licensed from another party for use on its adapter. An example of this is the once popular EMU10K1 DSP, developed by E-mu Systems, but shipped in Creative's own SB Live sound adapters as well as licensed and adapted for use in other manufacturers' adapters.

Polyphony is a term you often see applied to sound adapters. In music, this refers to a composition with two or more independent melodic components blended together.
With audio technology and specifically sound adapters, polyphony refers to the maximum number of voices that the adapter's synthesizer can play at any one time. Each voice is measured as one note generated by one instrument.

Sound adapters can generate voices either from hardware or software (drivers and support files), but many today combine both to offer a much larger number of voices.

Digital to Analog (DAC) and Analog to Digital(ADC) Converters

These two 16-bit (minimum) or 32-bit or more converters, along with a sample rate generator, provide the core of the digital audio component on a sound adapter. The DAC takes care of sending audio out in converted analog format through the Line-Out jack, while the ADC is responsible for receiving an analog signal and digitizing it through the Line-In jack (or microphone jack).

Some sound adapters may have more than one DAC/ADC convertor.

Sample Rate Generator

The sample rate generator's job is to clock both the converters and work with the CPU that is scheduling the samples. Most of them use discrete rather than variable or arbitrary sample rates, usually fractions of either 44,100 Hz and/or 48,000 Hz. Also, some sound adapters record and playback at differing samples rates. For instance, a sound adapter may only record at 44,100 Hz but play back audio at various rates.

Musical Instrument Digital Interface (MIDI)

The Musical Instrument Digital Interface (MIDI) represents a standard, approved by the electronic music industry, for music hardware to attach to the computer through a sound device and for these devices to be controlled and manipulated through the computer.

Without such an interface, you would be left to record sound through analog devices such as a tape or cassette recorder and then find a way to convert that magnetic media-stored sound into binary format that the PC can understand. Such conversion usually involves a loss of audio quality, compounded by what is likely to be less than professional recording quality from a standard analog recording device.

Often called the binary equivalent of ordinary sheet music, a MIDI file doesn't store the actual music but instead the instructions to the sound card on how to reproduce the music the composer designated. For this reason, the identical MIDI file can sound markedly different when played on different sound cards of varying abilities.

There are three generally-accepted MIDI standards, including:
• General MIDI - original standard, still supported by most major sound adapters
• Basic MIDI - a subset of General MIDI offered by Microsoft
• Extended MIDI - a subset of General MIDI also offered by Microsoft

A MIDI port with its standard 5-pin DIN connector is the connection point for external audio add-on devices such as MIDI keyboards, digital instruments like drumpads and special effects consoles. On some sound adapters, the game port and/or joystick port and the MIDI port are essentially the same. The MIDI port provides the pathway to the MIDI synthesizer, of which there are three major synthesizer types currently supported:

• FM Synthesizer
• WaveTable Synthesizer
• Physical Modeling or WaveGuide Synthesizers

Every MIDI interface supports at least 16 channels, and each channel represents a specific instrument. Higher-end sound adapters like the SB Live Platinum may have multiple interfaces (SB Live has 3), allowing for 3 times the minimum number of channels/instruments.

Sidebar: Why is a Game Port on a Sound Card?

Ever wonder why it's the sound adapter that has a game port? If you stop to think, it makes logical sense.

When the first true sound adapters arrived, sound wasn't a system requirement beyond the need for being able to emit a series of beeps to alert the user to a problem. But neither was gaming. While PC games were already popular, the typical PC was not considered the gamer's dream system (for one reason, because of the rudimentary audio and video).

Thus, you had two very optional device needs that could be effectively fulfilled through one board. Plus, games tended to use sound. If you had a sound adapter at all in those days, it was usually there for game sounds. Design-wise, they make a nearly perfect match and that union has remained with us for the better part of two decades.

Also, the typical sound adapter-based MIDI port is just an adaptation of the standard game port connector. It wasn't until the arrival of the multimedia PC movement (adding a sound adapter, speakers, CD-ROM, better video with greater emphasis on graphics, and microphone to more systems) in 1990 and after that a sound adapter became standard issue.

Sound Adapter Connections

A reasonably diverse range of devices related to sound production, recording, or transmission can be installed to the jacks and connectors on a sound adapter. Typically, these are located at the back of the PC where the sound adapter or bridge from the motherboard-integrated audio chip interface. Some devices, like internal CD-ROM drives, connect instead with a thin connector cable running between its position in a drive bay and the expansion bus or motherboard where the sound adapter is located.

The following devices may be installed to them and used by or with the sound adapter:

• Speakers (amplified)
• Headphones (mono, stereo)
• Digital input sources (examples: CD-ROM or DVD-ROM drive, digital audio tape (DAT) drive)
• Analog input sources (examples: microphone, CD player, tape player, or radio)
• Digital output sources (examples: CD-R, CD-RW, DVD recordable and DAT drives)