Karbosguide.com - Module 7c1.

PC sound


The contents:

  • An introduction
  • The synthesizer
  • The A/D conversion
  • Sampling the Wav files
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  • 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.

    On the first pages we shall describe the traditional sound card concept (the Sound Blaster compatible sound card). Then follows something on the newer technologies.


    Introduction

    Sound cards have a minimum of four tasks. They function as:

  • Synthesizer
  • MIDI interface
  • Analog-to-digital conversion during the recording (A/D).
  • Digital-to-analog conversion during the playback (D/A). All elements are to be explained on these pages, so please read on.

    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

    FM synthesis

    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 is and sounds like the artificial sounds it consists of.

    Wave tables - sampling

    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. Wave table is used in Sound Blaster's AWE card.

    Physical modeling

    Physical modeling synthesis is 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 original Sound Blaster Gold card contains 14 instrument sounds, which are created from physical models.

    Testing the sound

    The basic quality of a sound card can be tested by playing a MIDI 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. The SB AWE64 card has 64 voices, while SB16 only has 20 voices.

    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.


    About sampling

    As mentioned is the basic concept of digital recording of sound is called sampling. You can record any sound you want into a sample (a Wav file) if you have a sound card and a microphone. The sampling can be done in various qualities:

  • 8 bit or 16 bit sampling
  • 11, 22 or 44 KHz (kilohertz)
  • Stereo or mono

    The number of kilohertz tells how many thousand times per second the sound will be recorded.

    The quality of the sample

    A sample is like a tape recording - it can be good or less good. The recording range from low end, as recorded on the cheapest cassette recorder, to hi-fi recordings in CD quality. Here is an image from my setup, where I can choose between different qualities for recording:

    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.

    File sizes

    Using 2 channels stereo and 16 bit sampling at 44.1 KHz, the bit stream can be calculated as this:

    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:

    Replay
    Number of bytes
    One minute
    10 MB
    One hour
    605 MB
    74 Minutes
    746 MB

    Here you see the settings in a Wave program:

    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 Wav files

    If you look down in your PC, you will find plenty of Wav files. I did a little search, and this showed up:

    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.


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    Learn more

    Also see: Module 7d - about digital music: MP3s, MODs etc.

    Read about video cards in Module 7b .

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