On 26/07/12 18:24, Bill Unruh wrote: > On Thu, 26 Jul 2012, Torquil Macdonald S�rensen wrote: > >> Hi! >> >> I'm having a problem with my microphone inputs, and the master volume doesn't >> seem to be a master volume. In more detail: >> >> Part A of problem (microphone bleed): >> >> 1) In my headphones, I can hear the signal picked up by the laptop "Internal >> Mic" if "Internal Mic Boost" is maximised, even though "Internal mic" is >> minimised. It can also be heard out of the speakers when not using headphones, >> but for now I'm only using headphones. > > What is the problem? Remember that mic level usually does not go from 0 fbut > from some minimum to a max. Ie, the slider all the way down will correspond to > -30dB or something. If you then have mic boost as well, well it will be > audible. Sure, I have some experience with conventional audio equipment, e.g. analogue multi-channel mixers and so on used in professional audio. -30dB is not nearly enough suppression at the fader minimum position (if that is what ALSA uses), and apparently it is not really a hardware limitation, since I don't have the same trouble on Windows 7 (I'm dual booting). Or perhaps Windows provides additional attenuation in software somehow? The problem is that I think it should be enough to minimise only one fader, not two, in order to get rid of any playback of signals picked up by the internal mic (or external mic for that matter). If I'm working with a weak input signal that requires a maximised mic boost, and simultaneously monitoring it, I need to minimise both the monitoring and boost levels to get rid of the microphone sounds in my headphones. It should be enough to reduce one fader, the monitoring level. > > Secondly, there are two controls. One is for the "monitoring" and one is for > the volume going to the recording input. Ie, the sound card has two volume > contrrols, one affecting the recording level. Yes, this problem is only about the monitoring level and the boost level, not capture levels. >> >> Part B of problem (master volume): >> >> 3) The signal levels heard in the above cases, and also the level heard when >> actually increasing the "Internal Mic" and "Microphone", is independent of the >> "Master", "Headphone" and "Speaker" faders! I thought those were supposed to act >> as master volumes, in other words no sound should be possible if they are >> minimised? > > No. They are volume faders. not on off switches on many sound cards. Also they > often do not control the volume of the monitoring. When I said "no sound should be possible", I really meant "the sound level should be inaudible", because in my experience that is what happens on reasonable audio equipment. And when a systen has only one output (the headphone output is the only activated output when headphones are connected), the "Master" should control that level (hence the name). Otherwise it is redundant, since I already have "PCM", "Speaker" and "Headphone" faders. As it is now, I must minimise three faders: "Master", "Internal Mic", "Internal Mic Boost", to silence the computer. Or "Master", "Mic", "Mic Boost" if an external mic is connected. Surely one would expect e.g. that the "Speaker" fader should completely control the speaker sound level? Or that the "Headphone" level should completely control the headphones sound level? They do not do this on my system when microphone monitoring is involved, or when the microphone boost is maximised. Perhaps this is not how the sound card works in hardware, for some reason or other. But on Windows 7, the mixer behaves in a way that is more in line with traditional audio equipment. I.e. the Master fader can be used to silence the output completely, and minimising the microphone monitoring level makes any output of microphone signals inaudible, regardless of the microphone boost setting. Best regards Torquil Sørensen ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Alsa-user mailing list Alsa-user@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-user
