Sound Cards
The sound card (also called an audio card) is the part of a computer which manages its audio Input and output.
It is usually a controller which can be inserted into an ISA slot (or PCI for more recent ones), but more and more Motherboards include their own sound card.
Sound Card Connectors
The main components of a sound card are:
- The specialized processor, called the DSP (digital signal processor), which does all the digital audio processing(echo, reverb, vibrato chorus, tremolo, 3D effects, etc.);
- The digital to analog converter, or DAC for short, which converts the computer's audio data into an analog signal for being sent to a sound system (such as speakers or an amplifier);
- The analog to digital converter, or ADC for short, which converts an analog input signal into digital data which a computer can process;
- External input/output connectors:
- On or two standard 3.5 mm line‐out jacks, normally light green in color;
- A line‐in jack;
- A microphone input (sometimes called Mic), usually a pink‐colored 3.5 mm jack;
- An SPDIF digital output (Sony Philips Digital Interface, also known as S/PDIF or S‐PDIF or IEC 958 or IEC 60958 since 1998). This is an output line which sends digitized audio data to a digital amplifier using a
- Coaxial cable with RCA connectors at the ends.
- A MIDI connector, usually gold‐colored, which is used for connecting musical instruments, and can serve as a game port for plugging in a controller (like a joystick or game pad) which has a SUB‐D 15‐pin connector.
- Internal input/output connectors:
- A CD‐ROM/DVD‐ROM connector, with a black socket, which is used to connect the sound card into a CD‐ROM's analog audio output using a CD Audio cable;
- Auxiliary inputs (AUX‐In), with white sockets, used for connecting internal audio sources such as a TV tuner card;
- Telephone answering device connectors (TAD), which have a green connector.
Components:
The
modern PC sound card contains several hardware systems relating to the
production and capture of audio, the two main audio subsystems being for
digital audio capture and replay and music synthesis along with some glue hardware.
Historically, the replay and music synthesis subsystem has produced sound waves
in one of two ways:
1.
Through an internal FM synthesizer
2.
By playing a digitized, or sampled, sound.
The
digital audio section of a sound card consists of a matched pair of 16‐bit digital‐to‐analogue (DAC) and analogue‐to‐digital (ADC)
converters and a programmable sample rate generator. The computer reads the
sample data to or from the converters. The sample rate generator clocks the
converters and is controlled by the PC. While it can be any frequency above
5kHz, it's usually a fraction of 44.1kHz.
Most
cards use one or more Direct Memory Access (DMA) channels to read and write the
digital audio data to and from the audio hardware. DMA‐based cards that
implement simultaneous recording and playback (or full duplex operation) use
two channels, increasing the complexity of installation and the potential for
DMA clashes with other hardware. Some cards also provide a direct digital
output using an optical or coaxial S/PDIF connection.
A
card's sound generator is based on a custom Digital Signal Processor (DSP) that
replays the required musical notes by multiplexing reads from different areas
of the wave table memory at differing speeds to give the required pitches. The
maximum number of notes available is related to the processing power available
in the DSP and is referred to as the card's "polyphony".
DSPs
use complex algorithms to create effects such as reverb, chorus and delay.
Reverb gives the impression that the instruments are being played in large concert
halls. Chorus is used to give the impression that many instruments are playing
at once when in fact there's only one.
