Dither

You record at 24 bits but needs to convert to 16 bits to create a CD.
Inevitably you have to reduce the 24 bits to 16.
This will result in quantization errors.

Spectrograph Plot of a 24 Bit 100Hz Sine Wave

 

Spectrograph Plot of a 24 Bit 100Hz Sine Wave Truncated to 16 Bits

 

Spectrograph Plot of 24 bit Sine Wave Dithered to 16 bits

 

Adding dither is mixing the audio with some random noise.

It has two effects:
The spikes disappear by adding dither.
The noise floor increases.
That is the paradox of jitter; you get a more natural sounding recording by adding noise!

References

Dither Explained. An explanation and proof of the benefit of dither for the audio engineer. Nika Aldrich - April 25, 2002

Ozone Dithering Guide - iZotope, 2004

DIther - Wikipedia