Compared to...

Studio scene comparison (higher sensitivities)

Nikon's approach to noise reduction has always been chroma (color) noise reduction first, then relatively mild amounts of luminance noise reduction. This tends to leave its high sensitivity images looking more detailed but with potentially more visible luminance 'grain' noise (which isn't generally as objectionable as the more digital-like blotchy color noise).

ISO 1600

Nikon D300 Canon EOS 40D
Sony DSLR-A700 Olympus E-3

ISO 3200

Nikon D300 Canon EOS 40D
Sony DSLR-A700 Olympus E-3

ISO 6400

Nikon D300 Sony DSLR-A700