User:Shmimple7/Parametric Stereo

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Parametric Stereo (abbreviated as PS) is an audio compression algorithm used as an audio coding format for digital audio. It is considered an Audio Object Type of MPEG-4 Part 3 (MPEG-4 Audio) that serves to enhance the coding efficiency of low bandwidth stereo audio media.

Background
Parametric Stereo is considered a lossy compression algorithm.

Mechanisms/Physics
Parametric Stereo digitally codes a stereo audio signal by storing the audio as monaural alongside a small amount of extra information. This extra information (defined as "parametric overhead" ) describes how the monaural signal will behave across both stereo channels, which allows for the signal to be in stereo upon playback.

Advanced Audio Coding Low Complexity (AAC LC) combined with Spectral Band Replication (SBR) and Parametric Stereo (PS) was defined as HE-AAC v2. An HE-AAC v1 decoder will only give mono sound when decoding an HE-AAC v2 bitstream. Parametric Stereo performs sparse coding in the spatial domain, somewhat similar to what SBR does in the frequency domain. An AAC HE v2 bitstream is obtained by downmixing the stereo audio to mono at the encoder along with 2–3 kbit/s of side info (the Parametric Stereo information) in order to describe the spatial[1] intensity stereo generation and ambience regeneration at the decoder. By having the Parametric Stereo side info along with the mono audio stream, the decoder (player) can regenerate a faithful spatial approximation of the original stereo panorama at very low bitrates. Because only one audio channel is transmitted, along with the parametric side info, a 24 kbit/s coded audio signal with Parametric Stereo will be substantially improved in quality relative to discrete stereo audio signals encoded with conventional means. The additional bitrate spent on the single mono channel (combined with some PS side info) will substantially improve the perceived quality of the audio compared to a standard stereo stream at similar bitrate. However, this technique is only useful at the lowest bitrates (approx. 16–48 kbit/s) to give a good stereo impression, so while it can improve perceived quality at very low bitrates, it generally does not achieve transparency, since simulating the stereo dynamics of the audio with the technique is limited and generally deteriorates perceived quality regardless of the bitrate.

History
Parametric Stereo was first introduced in 2005 by the EURASIP Journal on Advances in Signal Processing. [why was it made, how was it made, for what purposes?] WRONG