Comment 9 for bug 1639499

Triangular-PDF is just the type of noise which is added for dither, to replace the quantization noise.

Noise shaping:
The inverse quantization error of sample N is feed back as noise for sample N+1
You can also put fancy filters into the feedback loop and add random noise as well.

Like shown here:
http://www.production-partner.de/wp-content/uploads/2015/03/Delta-sigma-noise-shaper.png

This is implemented in https://sourceforge.net/p/sox/code/ci/master/tree/src/dither.h