*why is there still noise even when...

[steve]

My main aim is to have the highest quality possible

The purpose of dither is to provide the highest quality possible when downsampling to a lower quality format (bit-depth) http://en.wikipedia.org/wiki/Dither

and when I silence the audio sections in editing and remove background noise I want my final product to precisely match that which I edited

If you use "Rectangle" dither then absolute silence will stay as absolute silence, but there will still be some degree of smoothing of quantize errors (though not quite as good as "shaped" or "triangle" dither).

I want my final product to precisely match that which I edited - same quality.

Unfortunately that is not possible (in Audacity or any other program).
Converting from a high quality format (32-bit float) to a low quality format (128kbps MP3) will always loose some sound quality (in the same way as converting a high resolution bit map image to a highly compressed JPEG will reduce image quality of a picture).

To disable dither, go to "Edit menu > Preferences > Quality" and set "dither" to "none".
You could also try changing the type of dither to "Rectangle" in the same place.
The "Real-time conversion" setting for dither should be "None".

After setting the dither settings as you want them, Export as 16-bit WAV 44100Hz for import into Premiere Pro.

Out of curiosity, what are you doing in Premiere Pro? I though that was a video editing program.

[npags711]

Didn't hear back on the last post Steve so let me know when you catch a minute - thanks

[kozikowski]

You could do everything in 16-bit and avoid the dither and sampling problems altogether. It's only if you get into very serious effects, noise reduction and production tools that 32-floating buys you anything. If all you're doing is capturing vinyl and making a Music CD (for one example) 32-float may actually be worse because of conversion errors.

Music CD standard is 44100, 16-bit, Stereo. Television sound is 48000, 16-bit, Stereo.

Just because Audacity defaults to 32-floating doesn't mean it's best for every job. Audacity has a number of awkward defaults. When you get into quality issues you rapidly run into environment issues as well. How are you listening? Model and part numbers.

The test tone is not supposed to be sharp and clear. Pure tones sound flat and uninteresting. Sharp and clear is distortion.

Isn't this fun?

Koz