dean Wrote: > On Nov 14, 2005, at 1:34 PM, Patrick Dixon wrote: > > > > >> Given that the Squeezebox has a 24 bit output, the rounding error > >> should be down at around at 138-144dB, not 90-96dB and I have a > hard > >> time believing that the effect would be as obvious as you state at > >> that level. > > > This is simply incorrect - the rounding error is at the 16th bit of > a > > 16-bit audio signal, therefore it is at -90/96dB. > The output audio signal is 24 bits. The rounding error is at the > least significant bit there.But this is the 16th bit of the sampled data - > therefore the error noise has 16th bit significance - not 24th > > The source material is 16 bits and when you scale that value it > necessarily needs to be rounded to the output resolution.Indeed, and that's > fine as long as you don't start discarding resolution> > > > It's not just that I like it better - it's also that it's 'correct' > to > > maintain the accuracy of the original digital data - in a similar > way > > as it's 'correct' not to sample rate convert 44.1KHz audio to 48KHz > > > (as > > some other manufacturers do). > It's a tradeoff between the accuracy of the gain control vs the > rounding error at the 24th bit.But the gain control accuracy is insignificant > conpared to the rounding error. How can you argue that you can't hear the difference etween a rounding error at 16 bits (or 24 as you think it is), but want to preserve volume control accuracy to two decimal places of a dB?[> > > > Even if you don't understand it and won't > > take my word for it, the difference between the 'rounded' volume > > multipliers and the unrounded volume multipliers is so slight that > it > > cannot possibly have a negative effect! > Yet they can have a positive effect?YES!!!!> > > I can believe that it does sound better in some cases because you > would be rounding up the gain value. The oldest trick in the stereo > salesman's book is to turn up the volume to make something sound > better.I'm completely aware of that (it was me that first suggested it to jhwilliams earlier in this thread before I listened properly and tracked this down, but it is not what is happening here. > > I'm not trying to be difficult here, but I do want to understand this > > before we make a change.I'm not trying to be difficult either - I'm trying to > help you! I have patched my code and I'm perfectly happy that a) it's correct and b) it sounds correct, but I'm concerned for Slim Devices that you should release code with such a significant audio quality bug. I'm trying to help you avoid a mistake. > Another proposal moved the 8 to 16 bit > threshold from -35db to -30dB. What's the right value for this?The right > value is one as low as possible, but where the resolution of the volume control is still sensible. Obviously if the volume multiplier is changing less than 1 bit (ie not changing!) between steps - it's time to ditch the modulo 256 bit. -35dBs is fine for this, I could live with -30dB because I never listen down at this level, but in the interests of 'getting it right' and pleasing the majority of your users, you should stick to -35dB. Or even better, the exact point at which the volume control mutiplier stops changing at modulo 256.
-- Patrick Dixon www.at-tunes.co.uk ------------------------------------------------------------------------ Patrick Dixon's Profile: http://forums.slimdevices.com/member.php?userid=90 View this thread: http://forums.slimdevices.com/showthread.php?t=17269 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
