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!