Noise in rendered silence.

[semiquaver]

I thought this deserved its own thread.

As AD80 noted in this thread http://www.kvraudio.com/forum/viewtopic.php?t=84875

I get noise when rendering silence whether dither is on or off.

Moreover as far as I can tell, silence rendered with dither should still be silent - dither should only be as loud as the least significant bit : ie in a 24-bit linear track being truncated to 16 bits the dither signal should be as loud as the lower 8 bits of the 24 bit signal. then audio activity in those lower 8 bits can cause the least significant bit to flip around and thus be audible in your 16-bit recording.

But when your 24 bit recording is silent then there isn't anything to push up into your 16 bit recording.

Dither is supposed to be added to the signal before truncation - there may be special issues when going from floats to integer as well. In any case this seems wrong to me and I do not see noise in DP when I render silence with dither enabled.

Platinum: am I wrong here?

[aldi]

i bet this all (ends are cut off, signal under -75db are cut off, noise on dither) comes to one rounding error in the signal path. maby somewhere is a float instead of a double variable or a variable is out of it's range for some calculation or a wrong placed braked in a calculation. sometimes these things are very hard to find, hopefully not in this case

[IIRs]

I suspect this is the same problem as the rendering issue.. my guess, like aldi, is that its just some silly little mistake. After all, real-time audio is pristine, so there can't be anything fundamentally wrong with T's engine.

Dither is supposed to be added to the signal before truncation - there may be special issues when going from floats to integer as well. In any case this seems wrong to me and I do not see noise in DP when I render silence with dither enabled.

You may possibly have touched on the issue of 'bit transparency' .. basically some mastering apps are clever enough to know when a 16-bit signal is not being altered in any way, and will pass the data unchanged rather than convert to 32-bit, re-dither, and truncate again. This could be important when trying to bring together material, some of which has already been mastered to 16-bit, and some of which has not.. but its probably not relevant to Tracktion until it grows CD burning functions and is marketed specifically as a mastering app.

[AD80]

I'm not sure what it is.

But all I know is I rendered 16bit files in Ableton, EnergyXT, Audition, FruityLoops, and Acid 2.0, and they all had completely flat silence. But Tracktion and Reason both had -90db silence.

(I'm surprised Acid 2.0 still opened on my sys )