Subject: Re: [linux-audio-dev] some basic sound questions
From: Paul Winkler (zarmzarm_AT_erols.com)
Date: pe marras 13 1998 - 02:33:17 EST
Michael Stutz wrote:
> I have some questions about very basic audio tasks and was wondering if
> anyone knew of tools that could do these things:
> * A sound meter or sound level tool that graphically displays the levels of
> sound currently coming into the soundcard's input jacks.
There's a command-line "meter" at ftp://184.108.40.206/pub/vu/
I haven't tried it-- I gather it's not a graphic meter, but a text
approximation to STDOUT???
> Programs like snd show the levels of a sound file (ie, after the fact), but
> I would like to see the levels at the inputs, so I can determine whether my
> mixer settings are wrong. The seems like a very basic feature -- maybe there
> are mixer programs that display this?
You'd think so, but I haven't seen one. But if you don't mind the
overhead of recording in Snd or DAP, they both have meters in the record
> * A tool for level-based recording. So you could set a certain level and
> when sound came in the input that was at or above that level, it would
> record. Richard King just brought this up on the linux-sound list, and
> nobody knew of any program that did this.
DAP has a "trigger" level slider in the record dialog box, it does
exactly what you want. Seems to work quite well. DAP only records AIFF
files but it's fairly trivial to convert those to something else...
> * A program to record audio post-facto, such as the Win95 "pfau" > (snip)... If you hear an audio bit that you want to save, you signal
> the program somehow and it keeps that last chunk in a timestamped file that
> you can then edit. (Hmm, with a /proc/audio on your system such a program
> would probably be trivial to write.)
Really good idea!
> Speaking of /proc/audio -- the paudio module at
> <http://source.syr.edu/~jdimpson/proj/> creates a /proc/audio file that
> allows you to save whatever data is currently going through the soundcard.
Yep, it sounds cool... but I discovered that it only works with a
specially-patched OSS-free, not OSS-Linux or ALSA. OSS-Linux now has a
beta-test pcm loopback device, which *might* be usable for such a
utility... except that I can't get it to work with Multitrack and the
OSS "play" utility, which are the only two apps I've found that allow
you to select the input/output device. Nearly all audio developers seem
to hard-code /dev/dsp into the app. Boo! People, please don't do this!!
OSS-Linux provides multiple /dev/dsp's, and I believe 2.1 kernels do
this as well. It won't matter if we have no applications that can use
As for ALSA, I've been looking through the API docs; there is something
mentioned about a pcm networking system, but I don't know if that
includes a loopback capability. I hope so.
> I think this is a basic, useful feature, and think it should be part of the
> standard /proc filesystem. Shouldn't it? How does one go about convincing
> the kernel folks?
I have no idea. Sounds good to me.
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