I do not claim to be an expert in sound cards. But I will try to describe what little I know about this technology. The sound capabilities of the PC are quite interesting. In the late 1990s, new and radical designs in sound technology appeared, and at the same time the MP3 wave swept the Internet society.
Sound cards have a minimum of four tasks. They function as:
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. Wave table is used in Sound Blaster's AWE card.
Some sound cards can import new sounds. They are simply downloaded to the sound card, which might have 512 KB (Sound Blaster AWE64) or 4 MB RAM (Sound Blaster AWE64 Gold) available for the user's own sounds.
The A/D conversion
You need a A/D conversion, when analog sound signals are recorded, i.e. from a microphone. The other way around, the D/A-converter is used when the digital sounds have to be reproduced into a signal for the speakers amplifier.
The acoustic waves are collected by the microphone and lead to the sound card. Here it is converted into series of digital pulses, which eventually are saved in a file. This way a sampling is an analog-to-digital conversion:
During the playback, the bit stream from the sample file is converted to analog signals, which end in the loudspeaker.
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 of your voice is analog, but the resulting the file is digital. The transformation from analog signals to digital data is done in the A/D converter of the sound card.
The number of kilohertz tells how many thousand times per second the sound will be recorded.
You record by sampling many times per second. The more frequently it is done, the better quality we get. The best would be infinitely sampling, which is not possible.
To record audio CDs the sampling is executed 44,100 times per second. This we call a 44.1 KHz sampling.
The quality is measured in kilohertz (KHz) and resolution (bit width) as you see above. The higher the KHz is, the better becomes the quality of the WAV file, but it also becomes bigger in file size. 8 or 16 bit sampling refers to how much data we spent on each sample. 16 bit gives a good quality.
2 channels X 16 bit X 44,100 samples per second = 176,400 bytes per second (since 8 bits make one byte).
This gives us the following file sizes of sampled stereo music in CD quality:
Number of bytes
Here you see the settings in a Wave program:
The Wav files
All these Wav files contain sounds in a digital form - samples. They only contain very few seconds of sound, because of the file size, which must not grow too big.
A Wav file will sound the same no matter which sound card you may have, be it a sound card using FM Synthesis or Wave table. The sound is in the file and not in the sound card!
These samples above are used as sound effects within Windows. Similar samples are used as material on music CDs and in the MOD format of digital music.
AU is another file format for samples. MP3 files are highly compressed samples.
Also see: Module 7d - about digital music: MP3s, MODs etc.
Read about video cards in Module 7b .
Copyright (c) 1996-2005 by Michael B. Karbo. www.karbosguide.com.