In the context of digital audio, Lossy Compression refers to the technique of discarding some audio data from the input file to produce an output file that is similar enough to the original to be usable while reducing the file size beyond the limits of known lossless compression techniques. The information selected for removal is chosen according through various methods ranging from a simple low-pass approach to complex psychoacoustic models.
Benefits of Lossy Encoding: Space Savings
Downsides to Lossy Encoding: Generational degradation Perceptual non-transparancy due to either insufficient bandwidth, incorrect algorithm, inherent limitation of the format.
General Lossy Encoding Techniques
Low-pass filter Decrease in resolution for noisy passages
Does Lossy Encoding Preserve Surround Information?
Depending on the encoder and settings, degradation of surround imaging may happen. Use higher bitrate to prevent this from happening. Mid/Side stereo of LAME or AAC does not destroy surround information. Also MPC preserves surround information with standard settings reasonably well. The lower the bitrate, the worse you can expect the surround imaging become.
List of common lossy formats
- Advanced Audio Coding (AAC, also improperly known as MP4 or M4A)
- Musepack (also known as MPC, formerly known as MPEGplus or MP+)
- (Ogg) Vorbis
- Speex (speech only)
- Windows Media Audio (WMA)