Adobe 22011292 User Guide - Page 47

ADOBE AUDITION 33 User Guide DVI/IMA ADPCM (.wav) The International Multimedia Association (IMA) flavor of ADPCM compresses 16-bit data to 4 bits/sample (4:1) using a different (faster) method than Microsoft ADPCM, and has different distortion characteristics, which can produce either better or worse results depending on the sample being compressed. As with Microsoft ADPCM, it's best to save to this format from 16-bit rather than from 8-bit. This compression scheme can be a good alternative to MPEG; it provides reasonably fast decoding of 4:1 compression, and it degrades sample quality only slightly. Options Choose from the following: • 2 bits/sample, 8:1 • This option creates ADPCM .wav files with the highest compression ratio (8:1), but with the lowest number of bits. Select this option when smaller file size is more important than audio quality. Keep in mind that this compression rate is less compatible than the standard 4-bit, and may not be able to be played back on all systems. • 3 bits/sample, 5.3:1 -- The 3-bit ADPCM files produced with this option use a compression ratio of 5.3:1. Quality is better than with the 2 bits option, but not quite as good as the 4 and 5 bits choices. Some systems might have problems playing back files compressed with this option, especially stereo files. • 4 bits/sample, 4:1 -- This is the default option, which produces 4-bit files at a compression ratio of 4:1. • 5 bits/sample, 3.2:1 -- Use this option for the best quality, since more bits and a lower compression ratio are used. However, this compression rate is less compatible than the standard 4-bit, and may not work on all systems. Microsoft ADPCM (.wav) The Microsoft ADPCM format consists of 4-bit per channel compressed data, which provides 4:1 compression. Files saved in this format will automatically be expanded to 16-bits when loaded, regardless of their original resolution. For this reason, it's best to save to this format from a 16-bit waveform rather than 8-bit, as the quality will be much greater. Options Choose from the following: • Single Pass compresses files in a single pass. Use this option if you're in a hurry. However, the quality will be lower than if you use the Multiple Pass option. The time taken to read an ADPCM compressed file is the same no matter which option you choose. • Multiple Pass compresses files using multiple passes, which provides better quality. This is the default setting. • Block Size offers three size options, each with a different compression ratio and quality level. • Large (Default Quality), with a compression ratio of 3.98:1. • Medium (Good Quality), with an increased quality level, but because the compression ratio is a bit smaller (3.81:1), your files will be slightly larger than with the Large option. • Small (High Quality) offers the best quality ADPCM sound at a trade-off of larger files due to the smaller compression ratio (3.25:1).