What are Computer Sound or Audio Files?


Sound files, by their nature are quite large. Types that must fully load before they can play can cause long waits across dial-up speed lines. Most types of sound files are based on taking very frequent samples of the complex sound waves and digitally recreating those sound waves during playback. The faster the sampling, the higher the quality of sound, but larger the file. Low quality files are typically sampled 11,000 times per second. Medium quality is sampled 22,000 times per second, and high quality is 44,000 times per second. The low quality is akin to telephone sound, and not very good for listening to music. The high quality is similar to FM radio. File sizes may be reduced somewhat by compression techniques.
The earliest types on the Internet, first used with unix computers, use the .au and .snd extensions. These are apt to be the largest files for a given length of audio. Later sound files use the extensions .ai, .aif, .mp2 or .mp3, and .wav. Most modern browsers either have the capability to play these built in to the software or can play them with plug-in software, readily available from Netscape or Microsoft.

If your modem and connection are fast enough, it is possible under good conditions to feed a low to medium quality signal to you fast enough to play in real time over a dial-up connection. RealAudio was the first company to produce streaming audio files and broadcast of live events. These files have the .ra extension, and require you to download the RealAudio or RealPlayer software(the latter combines a streaming video capability, too) from the RealAudio site or buy it in a store. There are other forms of streaming audio appearing now, too, such as the audio components for QuickTime, Shockwave, and Streamworks.

MIDI, are another type of sound file uses a resident library of instrumental sounds from your sound card. This technique is called wave table synthesis. The files, instead of reproducing sound waves based on sampling, feed information to the software and sound card on pitch, duration, instrument or type of sound, and other technical characteristics of the sound. The card pulls the pre-recorded instrumental sounds from its wave table. These files can be much smaller than those based on sampling, even with many instruments. If your sound card supports MIDI (Musical Instrument Digital Interface) files (with the .mid extension), you can play MIDI files. Quality may vary greatly, depending on the sound card and you can hear very different sounds from different computers. At its best, it can be very, very good. At its worst, it is horrible. It is very popular, though, and large libraries have been built up of MIDI files. See Sources below. MIDI, as an audio standard for musicians, can be used with keyboards and synthesizers independent of computer systems, too.

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