On a fine day, 02-02-2004, Jules Bromley wrote: >Just had to say that your précis of bit-depth, sample-rate and dither >principles was one of the most concise, helpful and clear (not to mention >accurate - amazing how many people will happily spout nonsense on these >subjects!) accounts I have ever read. <blush> Thank you for the compliments -- I'm glad you liked it (and agreed with the technical stuff) >I do have one question for you though, which is always an issue for me with >DAW's. If you're bussing out to a mixer instead of mixing in the box (in my >case 48 channels of 24bit audio out to external boxes and a Mackie D8B), >does Logic automatically dither down from it's internal mixer's bit depth >(32 bit float in this case) to 24 bit fixed, or does one manually need to >add dither to all those output busses? Woh... I don't think my 'expertise' stretches that far. My guess would be that it's "obvious" that Logic dithers to 24 bit, but that's just based on... well, nothing much really :). My intuition would say something like: if you use an I/O plug-in, the external gear surely gets the audio delivered in a useable format (I hope), which means 24 or 16 bit. Likewise if you assign a bus or output object to a physical output, Logic surely delivers the audio to the output in a usable format as well, shouldn't it? I mean, is there any gear out there that can actually read/use 32-bit float? I wouldn't know, but have always thought the answer to that is: no. And if that's correct and 32-bit float is typical for Logic but for nothing much else, then it would be bizarre if the output carried a 32-bit float signal... But then you say: >When I used Cubase SX and Nuendo, I had to use busses routed >to individual outputs with Waves L2 limiters across every bus dithering down >to 24 bits, to ensure that all my bus outs were being looked after properly. >This is because (as I understand it) the bus outs in Nuendo do not >automatically apply dithering when dropping from 32bit float to the output >bit depth. Now this has me all confused, meaning the "obviousness" of the foregoing maybe (or: apparently?) isn't that obvious at all. But... since 32 *float* is so fundamentally different from 24 bit *integer*, would external 24-bit gear be able to do anything sensible with 32 float _at all_? I mean, I can imagine how a 16-bit machine simply truncates incoming 24-bit data -- that's easy enough. But I can't really imagine what a 16- or 24-bit machine is supposed to do with 32-bit float data -- except dither it (which would make the entire matter a moot point -- who cares who does the dithering, the external box or Logic?), or reject it, or turn it into horrible noise or something like that. And: if you would have to dither to 24 bit, then how would you go about doing that? Does Logic offer a dither plug-in? I honestly wouldn't know, as I've never needed one... Having to use a 3rd party plug-in (like the Waves L2) would be extremely silly. So the best idea I can offer (which isn't very good, I know) is: just try it. If the result sounds 'regular' then most likely some form of dithering takes place somewhere -- either in Logic or in the external machine. If there's no sound at all, or it all sounds completely wrong, then you're potential problem apparently is an actual problem. I know this isn't much of an answer, but I really wouldn't know the _real_ answer. I'm just a simple mathematician who happens to understand the theoretical concepts, but who's never seen a spdif-cable in his life :-). >As far as I understand, whenever bit depth changes, dither should be used. Correct. The alternative is plain truncation of the data (i.e. throwing away the lower bits) which is undesirable. >Should I be doing the same with Logic, or does Logic use a fully >dithered mixer, including all the individual outs? I hope someone else can offer a definitive answer to this. I would be curious as well (if only for theoretical reasons :). -- Hendrik Jan Veenstra h @ k n o w a r e . n l Omega Art: http://www.omega-art.com/