Sound Forge and the Microsoft Audio Compression Manager

The Microsoft Audio Compression Manager (ACM) is a standard interface for audio compression in Windows. This interface allows applications such as Sound Forge to use compression algorithms provided by other companies.

Sound Forge fully supports audio compression through the ACM. This enables you to use any ACM-compatible compression. The best part of this support is you don’t have to learn anything new to use it! Sound Forge transparently opens compressed .wav files and provides all available compression formats for .wav files in the Save As dialog.

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Audio data compression and decompression

The first piece of the ACM allows you to compress and decompress audio data. Audio compression is used to decrease the amount of data required to represent a sound; this ultimately results in smaller sound files. However, there are drawbacks to using audio compression on your sound files:

In Sound Forge, any compressed .wav file can be opened as long as a compatible ACM driver is installed and enabled. If there is no compatible ACM driver available for a compressed .wav file, Sound Forge will inform you of the problem when you try to open it.

Saving compressed .wav files is as simple as choosing the compression algorithm in the Format drop-down list of the Save As dialog. Once a file has been saved as compressed, Sound Forge will always save changes to the file using the selected compression algorithm; you do not need to reselect the compression format each time you save. However, you can change the compression format or revert to an uncompressed format at any time with the Save As dialog.

Transparent playback and recording of nonhardware supported audio files

The Microsoft Sound Mapper allows audio data formats that are not directly supported by your sound card to be played and recorded. Sound Forge lets you use the Sound Mapper by selecting it for Playback and Record on the Wave tab of the Preferences dialog.

Using the Sound Mapper with Uncompressed Files

The primary use of the Sound Mapper for uncompressed sound files is for your convenience. You don’t have to convert the sound to a supported format before you listen to it:

Using the Sound Mapper with Compressed Files

The Sound Mapper allows you to play (and sometimes record) compressed sound files—even on sound cards that do not directly support compression—so you can play a sound file that is compressed with Microsoft ADPCM or the DSP Group’s TrueSpeech without decompressing the file first.

The Sound Mapper cannot always record compressed sound files because compressing sound data can be very processor intensive: the amount of time required is dependent on the compression algorithm and how it is implemented. Decompressing sound data is almost always faster than compressing the same sound data.

Sound Forge does not play and record compressed sound files directly. Rather, all compression and decompression is performed while opening and saving the sound files. Sound Forge saves compressed sound files using the best quality possible—something that cannot always be done in real time. Saving compressed sound files with Sound Forge will usually sound better than those recorded with audio compression.

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