Thanks for your input Steve > very short answer ;-) > there really is no need to dither to 24 fixed. > dithering adds noise at level below lsb - with 24 bits this > is so microscopic as to be unnecessary. Please don't think me pedantic or argumentative but .... lots of people say they can't hear the difference between 16 bits and 24bits, yet the industry is well and truly committed to 24 bit, not to mention 96K (which I confess I can't hear the benefits of blind). All of these microscopic differences eventually add up to an audible difference, and many of us rightly or wrongly set our standards as high as our resources (and capabilities!) allow. For me, dithering when changing bit depth is a basic and fundamental principal of digital audio and I think most engineers, especially in the mastering field, would agree. Can we at least agree, that technically, dithering is the correct thing to do (otherwise why do the more respected plugin developers insist on it, even at far greater bit-depths?)? If so, I think it's only reasonable to want to know whether Logic is dithering or not. Finally, I hope you don't mind me quoting Joe Bryan of Universal Audio (below), whose views on all things audio I have the greatest respect for. Sorry if this thread is getting slightly anal, but I think there's a basic question which we could do with an answer to. Jules --------- Converting from 32-bit float to 24-bit fixed still requires dither because signals below -6dB have more resolution in float than they do in fixed. It's true that 32-bit float only maintains 24-bits of resolution, but the extra 8-bits used for scaling *maintain* this resolution at all signal levels. Think of it this way: float *always* maintains 24-bit resolution, regardless of level, and the worst case error is 1-bit or less. On the other hand, 24-bit fixed *only* maintains 24-bit resolution when the signal is between -6dB and 0dBFS. When the signal goes below this range, the upper bits are essentially unused (they're duplicates of the sign bit), so the signal resolution degrades as the level goes down. Every 6dB drop looses a bit of resolution. To make matters worse, headroom bits must be maintained (typically 2-3 bits), so the effective signal resolution at nominal levels is only 21-22 bits. Therefore, since fixed point resolution is less at lower signal levels while float resolution is unchanged at lower levels, dither must be applied when converting from float to fixed. Incidentally, dither can increase the effective resolution of a signal beyond the theoretical 6.028dB x N-bits resolution. The information carrying capabilities of perceptual data representations (like audio or visual signals) include not just the instantaneous signal representation (each individual sample), but also the spectral energy profile. Dither rearranges the quantization error energy in a way that maximizes information transfer. The total error energy is actually higher, but it's reorganized in a way that minimizes the impact these errors have on perception. We reccommend always leaving your audio data in 32-bit float format until the final mastering stage. Once all signal processing has been performed, resample (if necessary), and apply dither as the last steps before burning to the target media. The UAD-1 performs its internal calculations at a higher bit-depth than IEEE float, and uses UltraDither to reduce the internal resolution before transferring the data back to the host. For plugs like the CS-1, Nigel, DreamVerb, etc. that consist of multiple processing elements chained internally, the UAD-1 leaves the data in its internal resolution between processing elements.