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Audio Codecs

As their quality increases, sound files take up a progressively bigger chunk of your hard disk. To help reduce the load, codecs are used to compress digitized audio and then decompress it for playing. Windows 98 comes with a number of 32-bit codecs. Here's a list of the Microsoft codecs:

Adaptive Delta Pulse Code Modulation (ADPCM): This codec works by storing the differences between consecutive PCM samples. This allows ADPCM to store audio data in just 4 bits, which is a 4:1 compression ratio over 16-bit audio. This codec reproduces low frequencies well but tends to distort high frequencies. However, these distortions are barely noticeable at higher sampling frequencies.

Consultative Committee for International Telephone and Telegraph (CCITT) G.711 A-Law and µ -Law: Provided for compatibility with current Telephony Application Programming Interface (TAPI) standards. These codecs are supported by many hardware configurations but offer only a 2:1 compression ratio (from 16 bits to 8 bits per sample).

DSP Group TrueSpeech Software: This codec offers high compression rates for voice-oriented sound, which makes it a good codec to use when recording voice notes.

Groupe Special Mobile (GSM) 6.10: This codec offers real-time compression, which makes it a good choice for recording voice snippets with Sound Recorder. GSM gives you only a 2:1 compression ratio, but it lets you select from a relatively large range of sampling frequencies.

Interactive Multimedia Association (IMA) ADPCM: This is similar to ADPCM, because it gives you a 4:1 compression ratio over 16-bit audio. The advantage of IMA ADPCM is that it takes a little less time to compress files.

PCM Converter: This codec is included for use with older Sound Blaster and other 8-bit sound cards. It lets these cards play 16-bit audio clips. This codec also can convert the sampling frequency to a different rate for cards that don't support the original rate used to digitize a sound wave.


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