I have sound but the levels are very low. How do I increase them?

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Q: I must admit that I'm just getting my feet wet when it comes to Rivendell, so please be bear with me. We have just installed Rivendell using the RRABuntu install disk. Everything works fine as far as the automation itself. The problem is the audio output level is too low.

When I play the test tone on the Airplay screen, it shows a 100% output level. Measuring the actual output from the line/headphone jack, gives a reading of 27mv, or about -29dbv, with the output unloaded.

The Rivendell documentation says that the output ought to be -16 dbv, which even at that seems like a very low output level. This, after all, is a peak output level, not RMS or average, and the stored mp3 music is all controlled for peak levels. We should be able to run at -10 dbv and have plenty of headroom. In other words, we need an additional 20 db of "gain". The s/n is not adequate at the -29dbv peak level we are seeing.

I am not very knowledgeable about the Jack/Alsa system, although I have a rough idea how it works. What I can't figure out is how to adjust the output gain of the sound chip. I know the problem is not defective hardware. I have even gone to the trouble of trying two different (same model) motherboards, with the same result.

When using the same hardware with a regular Ubuntu distribution (using a live CD) and playing an audio file from the Web (an ogg file from the vorbis.com website) the sound card delivers clean output into 32 ohm headphones of several tenths of a volt.

There must be a way of editing a file somewhere to set the output level of the sound card higher, but I can't find it.

Will someone please explain this to me?

A: This is normally a matter of adjusting the sound card mixer level.

Two mixers that you can use are alsamixer and aumix

These are terminal programs so don't look for them in the menu. Open a terminal and type:

alsamixer

or

aumix

You can then adjust the levels with them.

The wikipedia has a good page about alsamixer that will help you to understand its interface and controls.

aumix's home page gives information on using it, but it normally is not installed by default.

aumix also has a gtk GUI-interface that the package will install a menu item to start it with. Try installing the package aumix-gtk with your package manager.

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