What is the difference between dithering options at mixing down export>audio screen?

Try the help file!:)

I don't fully understand yet either but here it is pasted from help:

Dithering
Whenever an audio signal is converted from a higher-bit resolution to a lower resolution, it is necessary to apply dither to avoid introducing undesirable quantization noise or harmonic distortion into the signal. You can select from four available dithering types.
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Rectangular

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Triangular

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Pow-r 1

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Pow-r 2

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Pow-r 3


Dithering. Whenever an audio signal is converted from a higher-bit resolution to a lower resolution, it is necessary to apply dither to avoid introducing undesirable quantization noise or harmonic distortion into the signal. The purpose of dither is to reduce the resulting distortion by adding low-level random noise or “dither” to the audio signal. Different mathematical calculations are used to generate dither, each method has advantages and disadvantages depending on the particular operation. SONAR features the Pow-r dithering process, short for Psycho-acoustically Optimized Wordlength Reduction, which can produce lower-bit files that sound indistinguishable from higher-bit source files. When this option is turned on, SONAR uses dithering when you export a higher-bit file at a lower resolution, or lower the bit depth of a project’s audio files by using the Tools > Change Audio Format command, or when you “render” audio (bounce, freeze, or apply effects).
SONAR Producer offers five kinds of dithering:
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Rectangular. Essentially white noise, no noise shaping. Advantages: least CPU-intensive, lowest signal-to-noise ratio, preferable to shaped dither when successive dithering can occur (e.g. bouncing, freezing). Disadvantages: suffers from intermodulation distortion, higher perceived loudness than Pow-r dither.

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Triangular. Higher level than rectangular, no noise shaping. Advantages: low CPU-intensive dither, superior to Rectangular as it does not suffer from modulation noise effects. Preferable to shaped (Pow-r) dither when successive dithering can occur (e.g. bouncing, freezing). Disadvantages: higher perceived loudness than Pow-r dither.

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Pow-r 1. Noise-shaped dither. Advantages: less CPU-intensive than Pow-r types 2 and 3, lower perceived loudness than Rectangular or Triangular. Disadvantages: less noise shaping than Pow-r types 2 and 3, not recommended for operations where dither will be applied successively (e.g. bounce and freeze).

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Pow-r 2. Noise-shaped dither. Advantages: lowest perceived loudness, highest quality settings, recommended for audio export. Disadvantages: highest CPU-intensive settings, not recommended for operations where dither will be applied successively (e.g. bounce and freeze).

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Pow-r 3. Same as Pow-r 2 except most CPU-intensive and transparent of all choices.