On Thu, Jul 16, 2015 at 06:15:42AM -0500, Martin G. McCormick wrote: > Joel Roth writes: > > Hi Martin, > > > Pulse audio requires D-Bus, and D-Bus is the underlying RPC > > mechanism of a large and controversial software stack > > developed to support desktop applications. > > Thank you for this good and quick explanation. > > > > > Apparently pulseaudio is unable to get D-Bus services, > > due to a dependency of the latter on X. > > > > So you need either to satisfy/finesse this dependency of > > D-Bus, or disable/remove pulseaudio. I've read but not > > tested apulse, a library that purports to presents a pulse > > audio API to applications such as skype that require them, > > relaying the audio to ALSA. > > It looks like pulseaudio has been the ghost in the > basement on my system for about ten years. > > For now, I took it off completely and killed the > process. Before the CS4236 went away, there was always a sound > device for Card 0 and, if I had a second sound card, there was > another sound device for the second card. It was typical to see > /dev/dsp linked to Card 0, an actual /dev/dsp0 device and > /dev/dsp1 for Card 1 and so on. Just for fun, I think I stuck in a > USB sound card in addition to cards 0 and 1 and predictably got > /dev/dsp2 plus a lot of strange audio that sounded like a bad > tape transport due to all the sound cards trying to write to > their little segments of memory at the same time on a 600-MHZ > Pentium. > > Back to the present, I still had PA (pulseaudio) > running, no official Card 0 and a USB-based Soundblaster Digi > acting as Card 1. At least that's what aplay -l said. > > I could run mplayer and the playback was excellent but > amixer for Card 0 only showed one control for left and right > front volume. > > After I killed PA, mplayer said it couldn't find any > cards as there was no /dev/dsp any more. I did however find > /dev/dsp1 for the SBdigi so I manually forced a link with ln -s > to link /dev/dsp to /dev/dsp1. Presto! mplayer was happy again > and played music and other audio files but the story isn't quite > over yet.
The snd_pcm_oss kernel module, when loaded, provides /dev/dsp for compatibility with OSS applications. Calling mplayer with --ao=alsa should play via the default ALSA device, and does not require /dev/dsp. One the main benefits of pulse audio is the convenience of having a separate volume control for each audio application. If you don't need that, maybe you don't need PA. I can't comment on whether PA provides any other audio processing, however there are many other ways to get a low-pass filter if you need one. I refer you to the Linux Audio Users mailing list, the authoritative source for linux audio questions. The ArchLinux forums and wikis are also a great resource. Cheers, Joel > > I'm thinking that pulseaudio does some signal > processing, also. Some of the sound files I listen to are 8-bit > PCM voice recordings made at 8000 samples per second. They're > just fine for recording two-way radio chatter. Mr. Nyquist is > happy because 3 to 4 KHZ is the highest frequency you will > usually hear over such communication so it doesn't sound much > different than it did when first heard over the air. > > Before I killed PA, the audio of those raw PCM > recordings sounded fairly normal. After I killed PA, you can now > still hear the audio but you can also hear the 8-KHZ sampling > which sounds like a cheap toy as most of those don't bother with > a low-pass filter but let your ears and brain do that. > > It is possible that pulseaudio is using DSP techniques > to shape the wave forms properly and then is up-converting the > samples that the sound card sees. You can't add any fidelity > that is not already there, but this would act as a very good > low-pass filter. > > I also got in to /etc/modprobe.d and added a line to > alsa-base.conf to make the SBDigi be card 0 until I can resurrect the CS4236 > and > this seems to have made everything work automatically again. > amixer now reports a full-featured sound card with all the > controls one needs to do good playback and normal recording. The > playback is actually better than the CS4236 was so now we have > some progress. After things settle down, I may put PA back just > for the signal processing but for now, it's best to keep things > as simple as possible. > > Again, thanks for the explanation of some of > pulseaudio's purpose in life. It is presently used in those > screen reader modules that allow the kernel to generate > synthesized speech so it isn't all bad but it sure helps to know > what it does. > > Martin McCormick > > > -- > To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org > with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org > Archive: > https://lists.debian.org/20150716111542.77fb622...@server1.shellworld.net > -- Joel Roth -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: https://lists.debian.org/20150716175957.GB28143@sprite
