On 2011-05-13 18:20, Tanu Kaskinen wrote: > On Fri, 2011-05-13 at 17:29 +0200, David Henningsson wrote: >> In short; if we e g have Mic Boost levels at (0dB, 20dB, 40dB and 60dB) >> and the user wants 30 dB, better have 20dB in hardware and +10dB in >> software than 40dB in hardware and -10dB in software, as the latter one >> is more likely to have digital distortion when the signal passes through >> the ADC. >> >> There is a longer email on this list a while back, explaining more of >> the philosophy behind, but I can't seem to find it right now. > > Ok, I think I understand why rounding down makes sense when recording. > With playback, however, rounding towards 0 dB is definetely broken. My > ability to think clearly happens to be currently a bit weakened, so I > have to ask you: what's so magic about 0 dB? Here's how I wrote it a while ago, quoting a thread named "Mic Input Volume Controls": " We want to maximise quality while avoiding digital distortion, that's basically the problem in a nutshell. We're assuming (sometimes incorrectly; but that's our best guess) that this golden spot will be achieved with all sliders at 0 dB. I think my approach makes sense, unless I'm missing something: If we're aiming for something above 0 dB, let's round down to make sure we avoid distortion, and if we're below 0 dB, let's round up to make sure we get maximum quality. And then we always start with the control that's closest to the physical hardware and work our way in. " Rethinking that, I don't think I've ever seen any playback volume control that goes above 0 dB. All HDA's I've seen go up to 0 dB only, whereas for recording there is both above and below 0 dB. Therefore the scenario you state has not crossed my mind. So maybe you're right about always rounding up with playback. If there actually was a say +6 dB switch and you wanted +4 dB, then we should do +6 dB in hw and -2 dB in sw as +4 dB in software would potentially cause digital distortion. Right? > With playback rounding should always be done up - > would it make sense to round always down with capture? Maybe, if we give up the thought of 0 dB being magic. -- David Henningsson http://launchpad.net/~diwic
