[pulseaudio-discuss] Simulating Mic Boost in Pulseaudio

Lennart Poettering lennart at poettering.net
Sun Jun 8 14:51:35 PDT 2008

On Tue, 13.05.08 01:18, T. H. (truxxon at googlemail.com) wrote:

> Hello all,
> For some reason, after moving from ALSA 1.0.15 to 1.0.16, my alsamixer does
> not display anymore the Mic Boost (+20dB) option for my digital microphone
> (of an Intel HDA ICH8), which is quite useful to enhance its capture volume
> in Ekiga, Skype etc.
> This annoying bug started me wondering if it is possible to simulate this
> mic boost using pulseaudio, which I use on top of ALSA.
> I was thinking about two possible solutions:
> 1) instructing pulseaudio to feed the output of the microphone capture
> source to some sort of amplitude multiplier module, which would become the
> default source. However, I don't know if there is such a module and how to
> plug it to the correct location.

PA can do digital amplification for all streams. However, we don't
expose that in the UI since most of the time this doesn't make much
sense, unless we'd have some kind of dynamic range compression code in
place to avoid clipping. it's my plan to add this eventually, but as
of now, we don#t have this, sorry.

> 2) forcing pulseaudio to accept a default source volume  >100%. I noticed
> that some channels allow me to choose up to 400% (e.g., the sink
> alsa_output.pci_8086_284b_sound_card_0_alsa_playback_0), but the one I
> assume the microphone uses
> (alsa_input.pci_8086_284b_sound_card_0_alsa_capture_0), for some reason,
> resumes its 100% position immediately after I choose something >100%. I
> don't know if this is the expected behavior, but it would be nice if I could
> force it to accept larger values in order to boost the volume of my digital
> mic, for instance, by changing some config file.

For sinks we limit our mixer settings for what the hardware provides
us with. Only if we do volume adjustments in software we thus allow
digital (software) amplifciation. And again, we don#t expose this in
the UI.


Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net         ICQ# 11060553
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

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