|
|
Nowadays our PCs are
equipped with all the gadgets that are required by us in our
day-to-day life. You need not to buy a sophisticated CD/DVD player
or a Hi-Fi music station if you have bought a modern PC. A single PC
replaces lots many electronic equipments that are used in our daily
life. Do you know how do your PC generate/ record sound. This
article gives an introduction about the PC sound card that does
excellent job for you without letting you know.
Introduction
A sound card does a minimum of four tasks. It functions as
• Synthesizer
• MIDI interface
• Analog/digital converter (A/D), when sound is recorded from a
microphone.
• Digital/analog converter (D/A), when the digital sounds have to be
reproduced in a speaker.
The synthesizer
The synthesizer delivers the sound. That is, the sound card
generates the sounds. Here we
have three systems:
• FM synthesis, Frequency Modulation
• Wave table
• Physical modeling
The cheapest sounds card use the FM technology to generate sounds
simulating various instruments. Those are true synthesizers. The
sounds are synthetic – it may sound like a piano, but it is not. FM
synthesis generates sound like artificial sounds.
Wave tables
Wave table is the best and most expensive sound technology. This
means that the sounds on the sound card are recorded from real
instruments. You record, for example, from a real piano and make a
small sample based on the recording. This sample is stored on the
sound card. When the music has to be played, you are actually
listening to these samples. When they are of good quality, the sound
card can produce very impressive sounds, where the "piano" sounds
like a piano.
Physical modeling
Physical modeling synthesis has arrived as a third sound producing
technology. It involves simulating sounds through programming. The
process is supposed to be rather cumbersome, but it should yield a
number of other advantages.
The basic quality of a sound card can be tested by playing a MID
file. Then you can easily hear the difference. There is also a
difference in how many notes (polyphony) can be played
simultaneously. If you want to compose your own music on your PC,
you use the sounds available on your sound card. The greater works
you want to write, the more "voices" you will need.
MIDI
MIDI (Musical Instrument Digital Interface) is a specification,
which was developed in the 1980's to communicate between
synthesizers. Since then MIDI has also become the standard, which
allows programs to play music through the PC sound card.
MIDI is a computer standard music format. You write compositions -
musical events - in the MIDI format. The MIDI files do not contain
the sounds but a description of how the music is to be played. The
sounds are in your sound card. For example a MIDI sequence can
describe the hit on a piano key. The MIDI sequence describes:
• The instrument
• The note
• The strength of the key hit
• How long to maintain the note
The only thing that is not covered is the sound of the instrument -
that is created in the sound card, and is totally dependent on the
sound card quality.
A MIDI recording is thus a recording of music on "note level,"
without sound. It is played by a module, such as a sound card, that
can generate the sounds of the instrument. MIDI files do not occupy
much space as compared with the pure sound (WAVE files). Therefore
they are often used over Internet.
MIDI interface for keyboards
A musical keyboard can be connected to the sound card with a
connector. That is called a MIDI interface. You can buy special PC
musical keyboards, or you can use one of the keyboard that is
available in music stores. It will work as long as the MIDI
connectors match. You connect your DIN connector to the piano
keyboard. In the other end of the cable is a DB15 connector to the
sound card. Then you can play from the piano keyboard through the
sound card. Of course it requires a program that can handle music,
but it works.
The A/D conversion
When you connect a microphone to the sound card, you can easily
record your own voice on the PC. The result is a small WAVE file
which holds a digital recording of the sound, which reached the
microphone. The sound is analog, the file is digital – the
transformation is done in the A/D converter in the sound card.
This sound recording is called a sampling. It can be done in various
qualities:
• 8 bit or 16 bit sampling
• 11, 22 or 44 KHz (how many thousand times per second the sound
will be recorded)
• Stereo or mono
Stereo sampling at 16 bit and 44 KHz gives the best quality, but the
Wave files will take up quite a bit more space.
The sound of the future
Until now PC sound has been totally dominated by the Sound Blaster
card. All sound cards had to be compatible with Sound Blaster, or it
would not sell. Obviously that is due to the numerous game programs,
which require a SB compatible sound card.
The new sound cards break away from the Sound Blaster compatibility.
This break involves many facets. Below I will describe some of the
tendencies in the sound technology.
Sound over the PCI bus
Newer sound cards can be connected on the PCI bus. The SB
compatibility requires the old ISA bus, which is really antique
today. With PCI you gain different advantages:
• The IRQ problems disappear.
• Signal/noise ratio can be improved with 5 dB.
• There is sufficient bandwidth (capacity for data transmission).
• The sound card workload for the CPU is less.
• We can drop the ISA bus, which takes up unnecessary space on the
PC system board.
The problem in moving the sound to the PCI bus involves existing
software. First of all old DOS games, which expect and demand the
Sound Blaster card with its IRQ- and DMA number. They will not work
with the new cards, unless special solutions are implemented.
Sound over the USB bus
We will experience very high quality sound systems, when the new USB
bus is implemented. The difference is that the sound card in the PC
will work totally digital. The sound signals are in digital form
when they are sent out on the USB channel:
Inside the PC there is a lot of electric (static) interference from
many sources. That can affect the integrity of the signals in the
sound module. With USB the noise sensitive digital/analog conversion
will take place in the speaker, and this results in a superior
quality. Both Philips and Altec Lansing produce USB speakers.
In the future we will see Hi-Fi speakers with built-in amplifier and
converter, which can receive pure digital signals (via USB). These
speakers will randomly be able to interpret data from Hi-Fi
equipment, PC, TV/video and other sources. Surely we will also see
sound cards and speakers for the FireWire bus, which is somewhat
similar to USB.
|
|
