Intensity Stereo

Intensity Stereo can be used to enhance quality for low bitrate encodings. An Intensity Stereo encoded subband contains only one encoded signal and this signal is spreaded over two channels, a base channel contains a "normal" resolution (-1, 1 . . .) and a vector channel only contains information about the signal to spread.

Member of Subband Samples


Intensity Stereo exists with 1 . . . 8 vector bits.
Mostly used are 1 and 2 vector bits. Note that these can also be coded using the normal encoding methods LR and MS coding with an empty channel. But normally you need a lot of meta information if the subbands have changing signal correlations.

Intensity stereo is not possible for Subband 0.

1 Vector bit:

Vector bits Left Signal Right Signal
0 +M/sqrt 2 -M/sqrt 2
1 +M/sqrt 2 +M/sqrt 2

2 Vector bits:

Vector bits Left Signal Right Signal
00 +M/sqrt 2 -M/sqrt 2
01 +M 0
10 +M/sqrt 2 +M/sqrt 2
11 0 +M

n Vector bits: 

    phi = M_PI * vector / (1 << n) - M_PI/4;  /* gives an angle between -45° and 135° */
    L   = M * cos (phi);
    R   = M * sin (phi);
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