[AudioI] Microphone connector gain?

[Matt]

On 4/1/21 4:55 am, Ron Patton wrote:
> Hi Folks,
>
> Any takers on this?
>
> 73,
> Ron / W4MMP
>
> On 1/1/2021 23:07, Ron Patton via People wrote:
>> Hi,
>>
>> I am using the AudioInjector Zero in a hardware project (an Amateur
>> radio transceiver).   The Zero is working well for audio output.
>> However the microphone input of the Zero does not appear to have the
>> gain needed for using a standard run of the mill computer headset.
>> Now, I'm not an audio expert by any means so some of the following might
>> not be correct (or actually stupid). But,  my assumption is a standard
>> computer headset uses an electret microphone element.  These need a
>> "bias" voltage to operate properly.   I have measured the voltage at the
>> Zero microphone connection and it is supplying ~2.5V which should be
>> sufficient.  OK, so far so good.   However, the Zero does not seem to
>> provide enough gain and the audio volume is a bit low.
>>
>> There are two things I have done to examine the issue.
>>
>> 1) Attached is the ALSA configure used to configure the Zero.  It is the
>> file supplied when installing the test routines supplied by
>> AudioInjector.  It is attached to this email.  It is applied before
>> starting the application that uses the Zero (via Portaudio).
>>
>> 2) I have used ALSAMIXER to adjust the values that it displays (Mic
>> Boost and Capture).  These have been set to 100.  (Screen capture attached).
>>
>> So, the question is:  Is there something I can configure in ALSA (in the
>> attached asound.state.MIC.thru.test file) or otherwise to raise the gain
>> of the microphone connection?

Hi Ron,

It looks like the mixer is set correctly for the microphone. In the 
playback section, the input mux is set to microphone. The capture is set 
to microphone. You should have plenty of gain on the mic.

The microphone connector is the through hole capacitor looking footprint 
on the board. It isn't the stereo input connector. I can see that you 
measured the voltage on the microphone connector and that looks right.

There are some tests you can do with alsa mixer. One test I can think of 
will connect the microphone mixer directly to the analogue output of the 
audio codec. Enable the "Output Mixer Mic Sidetone Switch" and check 
that you can hear the microphone on the output of the sound card.

Also triple check that the GND and signal lines of the headset 
microphone are correctly connected.

Matt


>> --
>> 73,
>> Ron / W4MMP
>>
>>
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