GNOME Bugzilla – Bug 618551
Total deciBel gain is incorrect
Last modified: 2010-05-17 10:20:25 UTC
Hello, This report relates to the gnome-volume-control panel applet, which reports the total gain as a percentage and in deciBels whenever the user performs a mouse-over. The dB gain reported seems to assume that "all sliders at max" is the zero dB reference level. However, this is not always the case. For example, on my system, Master ranges from -46.5dB to 0dB but PCM ranges from -34.5dB to +12dB, so if these are both set to maximum the total gain will be +12dB. This is important because if I use those maximum settings and play any audio which peaks above -12dB, the output will clip and sound distorted. I find the percentages meaningless and I guess they are here to stay. :) But please keep the integrity of the deciBel scale so that "all sliders to 0dB" remains the foolproof recipe for clean audio. Cheers.
Are you sure that your audio card's drivers correctly advertises those dB levels? In any case, we only display what PulseAudio tells us, so you should poke the PulseAudio devs about this. This is the code in question: gdouble gvc_mixer_stream_get_decibel (GvcMixerStream *stream) { g_return_val_if_fail (GVC_IS_MIXER_STREAM (stream), 0); return pa_sw_volume_to_dB( (pa_volume_t) gvc_channel_map_get_volume(stream->priv->channel_map)[VOLUME]); }
Thanks for your informative reply. One thing still puzzles me about this though. If the incorrect total dB values are coming from pulse, how is it possible that the gnome-volume-control-applet is aware of the difference between "unamplified" and "100%"? If I right-click and open the Sound Preferences app, the output volume scale shows those reference points and they agree with the 0dB and all-sliders-max positions in the command-line version of alsamixer. In any case, I have filed a bug with pulse here:- https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/581650 Regards.