This seems like such a trivial problem but there is no answer anywhere. I'm trying to convert a 16bit song to 8bit so I can play it with a microcontroller. This creates a lot of noise. Every time I filter the noise in adobe audition, audacity and goldwave, it sounds great until I try to export it. The file saves on my computer then it was as though the filter has had zero effect on it. I'm pulling my hair out trying to make it work and it just won't. Does anyone know what is going on?
This is because Audition (and others) is using temporary 32-bit float files for destructive editing. That's why you can't hear the "real" 8-bit sound after you process converted files further. They are just not 8-bit at this time.
As for the quantization noise you are trying to remove, it's not possible. Though you can reduce its amount by enabling dithering and noise shaping. In Audition's "Convert Sample Rate" dialog try these settings:
Dither Type: Gaussian
Noise Shaping: Weighted (Heavy)
Adaptive Mode: Dynamic (Extreme)