Digidesign Pro Tools 8

Improve the sound of very low-level audio passages with dithering
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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.

STEPS

1. If your project doesn’t already include a master fader track, create one by going Track > New and specifying a stereo Master Fader.

1_NewMasterTrack

2. Select a destination for the Master Fader. Any audio arriving at this destination will be included in the dithered file.

2_SendToBus

3. Assign all outputs for tracks you want included in the dithered file to the same assignment as the Master Fader.

3_AssignTrackOuts

4. Click on the last Master Fader insert, and go Multichannel plug-in > Dither > POWr Dither (stereo).

4_InsertPlug

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.

5_PowR

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.

6_Bounce

TIPS

¦ 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.