Improve the sound of very low-level audio passages with dithering
OBJECTIVE: When converting a high bit resolution file to a low bit resolution file, use dithering to avoid unpleasant artifacts caused by truncating bits.
BACKGROUND: Converting from a higher bit resolution to a lower one truncates (removes) the extra bits. However, this can create distortion at low levels, as there are fewer bits of resolution. Dithering adds noise to very low-level signals to minimize the audible effects of this distortion. Applying dithering is common when converting from 24-bit or higher resolution to the 16-bit resolution required by CDs, but is applicable any time you need to convert from a higher bit resolution to a lower one.
1. If your project doesn’t already include a master fader track, create one by going Track > New and specifying a stereo Master Fader.
2. Select a destination for the Master Fader. Any audio arriving at this destination will be included in the dithered file.
3. Assign all outputs for tracks you want included in the dithered file to the same assignment as the Master Fader.
4. Click on the last Master Fader insert, and go Multichannel plug-in > Dither > POWr Dither (stereo).
5. Choose the desired options for the POWr Dither plug-in. When the object is to create a CD-compatible file, choose 16-bit for Bit Resolution; for Noise Shaping, Type 2 or 3 works well for pop mixes.
6. To bounce the file to the lower resolution and dither it, go File > Bounce To > Disk. In the Bounce dialog box that appears, specify the Bounce Source, File Type, and assuming you want to create a CD-compatible file, select Stereo Interleaved for Format, 16 for Bit Depth, and 44.1kHz for Sample Rate. Click on Bounce to create your converted and dithered file.
¦ In Step 1, do not create an Aux Input track. The Master Fader inserts are post-fader, which is important when using dithering plug-ins.
¦ In Step 5, under Conversion Options, Convert After Bounce is the preferred option for producing the most accurate results. Pro Tools bounces at the highest possible resolution to a temporary file, then does bit depth conversion and dithering to this file, writes the result to disk, and finally, deletes the temporary file.