Sessions & Tracks : Importing and Exporting Session Data : Audio Conversion on Import : Bit Depth Conversion and Dither

Bit Depth Conversion and Dither
If the Convert Copied Files on Import preference is enabled (Setup > Preferences > Processing), the following occurs when importing audio files with different bit depths than the current session bit depth:
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When importing audio at a lower bit depth than the session, Pro Tools converts the file to match the session bit depth by adding empty bits. For example, when importing a 16-bit file into a 24‑bit session, Pro Tools converts the file to 24‑bit.
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When importing audio at a higher bit depth than the session, Pro Tools automatically applies a preset, noise-shaped dither and converts the file to the session bit depth. For example, when importing a 24-bit file into a 16-bit session, dither is applied automatically and the file is converted to 16-bit.