[alsa-devel] [RFC PATCH] Inverted internal mic

David Henningsson david.henningsson at canonical.com
Thu Jun 21 03:15:27 CEST 2012

On 06/20/2012 03:31 PM, Takashi Iwai wrote:
> At Tue, 19 Jun 2012 09:43:07 +0200,
> David Henningsson wrote:
>> On 06/19/2012 05:07 AM, Eliot Blennerhassett wrote:
>>> David Henningsson<david.henningsson<at>   canonical.com>   writes:
>>>> On 02/28/2012 02:22 PM, Takashi Iwai wrote:
>>>>> At Tue, 28 Feb 2012 14:07:59 +0100,
>>>>> David Henningsson wrote:
>>>>> Is there a way we can
>>>>>> know the corresponding processing coefficients to set for ALC268 and
>>>>>> ALC272X as well?
>>>>> AFAIK, no, it was specific to the codec model.
>>>> Ok, then we can only hope for Kailang to supply this information if
>>>> possible. And if not possible we could attempt the workaround (when/if
>>>> we agree on it...) for these devices as well?
>>> Greetings,
>>> Any chance that there has been any progress on this?
>>> I have a machine with dmic and ALC272X (details below) that exhibits this
>>> problem, and can test any proposed patch.
>> We have a patch in for the Thinkpad U300s, but that one had a Conexant
>> codec.
>> I haven't had time to start working on kernel patches for the Realtek
>> ones yet, but meanwhile, I'm tracking known machines here:
>> https://bugs.launchpad.net/ubuntu/+source/alsa-driver/+bug/1002978
> Looking at the codec, it's not so trivial to port the inverted switch
> to Realtek.  In the input path of Realtek codecs, there is no
> individual capture volume/switch but only a central ADC volume and a
> MUX (or a mixer).

Yeah, that's part of why I haven't done it myself yet ;-)

 > I can think of a new boolean switch or an enum to choose whether to
 > shut off the right channel of the input-mux and the loopback volume.
 > But it's feasible only if it make sense to PA.

It seems possible that for ALC269 [1], you could switch path entirely 
(including ADC). I e, the internal mic would go 0x12 -> 0x23 -> 0x08 and 
the external mic would go 0x18 -> 0x24 -> 0x07. That way you could then 
label the volume control on 0x08 "Internal Mic Capture Volume" and 
"Inverted Internal Mic Capture Volume".

Do you think this is a good strategy, or would it lead to other problems 
(i e, what happens when you plug your mic in while actively recording)?

David Henningsson, Canonical Ltd.

[1] Example alsa info: 

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