2011/5/20 Colin Guthrie <gmane at colin.guthr.ie>: > 'Twas brillig, and Maarten Bosmans at 20/05/11 10:23 did gyre and gimble: >>> > With flat volumes, adding per-stream volumes to capture streams makes sense. >> With these changes, would it still be possible to record audio without >> software gain? As it is now, I can record from a source that has its >> volume set to 100% and be confident that I'm getting the signal direct >> from the soundcard. >> Is that still the case with the default source output volume? > > Yeah, that should still be the case. If you set the volume to of your > stream to 100%, even if some other stream is recording at 50%, the h/w > volume should be set to 100% > > Of course this is all rather arbitrary, as on my h/w the gain is 0dB > when I set the volume to 0.... at 100% it's +22.5dB, so to say direct > from the sound card at 100% is a little strange.... it's getting +22.5dB :) Ah, well I should probably have given some context. I'm recording from a 24bit/96Hz USB audio interface, so I want the PCM signal of the A/D converter as it is send over USB. This soundcard has no ALSA mixer element, so that part is easy. I just want to make sure Pulse doesn't do anything with that signal. > I guess the problem would come when recording two things at once. If you > set one to 100% (thus +22.5dB on my system) and one to the base volume > of the source it's attached to (thus ALSA's 0dB*), then the one that > expects to be recording at 0dB will actually get a signal that has gone > up to +22.5dB and then come back down in software to 0dB. This isn't > ideal, but then it's as non-ideal as it is currently and the use case > for recording two streams at the same time is rather minimal anyway, so > I don't think in all practicality, this is a big issue. Actually in my setup, I specifically put Pulse in the audio pipeline to be able to start multiple independent recordings simultaneously, without that requirement I could have just as well used ALSA directly (it's a headless audio server, not a desktop). The reason for this is that I want to be able to start a recording and separately decide whether the audio should be streamed (either RTP over LAN, or HTTP/Ogg/Vorbis over the internet, or both) and Pulse lets me start and stop the recording and live stream independently, which is great. > Of course if you don't use flat volumes and only use per-stream > recording volumes in your app, then the difference between the source > volume and the stream volume does come into play AFAIUI. But then if you > take the time to disable flat volumes, that's presumably a consequence > you can live with. I have some experimenting to do with Pulse git, but I might very well end up disabling flat volumes, thanks for the hint. > Col > > * I have one USB mic that reports it's range as +20dB to +50dB in alsa, > so the base volume for it is actually significantly below the ALSA 0 > point on the kcontrol! Maarten
