Hello, there has been some discussion about Mic Boost / Dock Mic Boost in the past already. Some have reported no Mic output at all without Boost, other say that enabling Boost will cause high noise on their systems. I have another point here that AFAICS hasn't been reported yet. It has been caused by the commit e6051cdf "alsa-mixer: Prefer moving "Capture" before moving boosts" (http://cgit.freedesktop.org/pulseaudio/pulseaudio/commit/?id=e6051cdf8db554c0bbd4257959c37a7ecc9c10c5) (see also https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/1085402). In short, on my system, input volume control is hardly possible above 25% because of this patch. The effect that I am seeing is as follows: I have two merged volume controls for my Mic, "Capture" and "Dock Mic Boost". They are applied by PA in the order encountered in the path conf file. On my system (Fujitsu Lifebook E744 with Realtek ALC282 Codec), the "Capture" Amp has a range of -18..30 dB in 0.75 dB steps, and "Dock Mic Boost" has 4 12dB steps (0, 12, 24, 36). PA merges these two controls to a single volume control with an overall range of -18..66dB. Normalizing at the max, PA converts this to -84..0dB, where the Boost comes in at -36dB, or 25% of the scale. The "base volume", calculated from the "offset" of the ALSA amp, is at -66dB or 8%. Because of the above patch, the "Capture" control is used first. Thus the range from -84...-36 dB (or 0..25%, because of the non-linearity of PA's volume control) is covered with "Capture". Above that level, "Capture" is always held at 100% and only "Doc Mic Boost" changes. This means that above 25%, there are only 3 steps that are actually possible: -24dB / 40%, -12dB / 63%, and 0dB / 100%. => There is no "smooth" volume control above 25%. The graphical volume controls don't reflect this; thus user control input volume is almost impossible at higher levels than 25%. Volume will appear to change non-predictably to users. By changing the ordering of "Capture" and "Mic Boost" in the path conf file /usr/share/pulseaudio/alsa-mixer/paths/analog-input-dock-mic.conf, I can get smooth changes over the whole dynamic range again. Therefore I reckon that commit e6051cdf should be reverted because the effect described here is general, while the noise level seems to be different between models: On my system, there is no perceivable difference in noise level if the overall volume is the same (thus, 30dB "Capture" + 0dB "Boost" has the same noise level as 18 dB "Capture" and 12 dB "Boost" or -6dB "Capure" and 36dB "Boost"). However, I tend to think that PA's concept of volume "merging" generally doesn't work well for a "Boost" control. The "Boost" is conceptually rather a switch than a slider. A dynamic range of 84 dB doesn't make a lot of sense for a cheap Mic like the typical laptop's Mic input. It would be more reasonable to nail the Mic Boost switch to a certain value that matches the hardware and just use the "Capture" dynamic range for volume control. In the short run, this could be done by setting Mic Boost to 0 or 1, e.g.: [Element Dock Mic Boost] required-any = any switch = select volume = 1 override-map.1 = all override-map.2 = all-left,all-right Ultimately, this shouldn't be hidden deeply in path conf files, therefore it would be necessary in the future that PA exhibit the "Mic Boost" control to users somewhere in the API / UI, unless some way is found to "guess" the optimal value for the boost on different systems. Please comment. Regards Martin
