david.henningsson at canonical.com
Tue Dec 20 07:57:01 UTC 2011
On 12/20/2011 06:54 AM, Len Ovens wrote:
> On Mon, December 19, 2011 5:33 pm, David Henningsson wrote:
>> (Please don't respond in private if anyone can benefit from the answer)
> I didn't realise I had, Sorry. I just hit reply without thinking.
>> You did not give me your alsa info, so I'm assuming it looks like mine.
>> The signal chain looks like this:
>> Physical Mic Jack => Mic Boost control => Capture control => ADC
>> So far I've seen only amplification on "Mic Boost", and most "Capture"
>> controls being able to do both amplification and attenuation. On my
>> computer, my Mic Boost goes from 0 dB to +30 dB (in 10 dB steps), and
>> Capture goes from -16.5 dB to +30 dB.
> Looks close enough, at least what alsa sees. I would suggest though, That
> the physical layout is more like:
> mic -> boost amp -> preamp (constant gain) -> capture (atten) -> ADC
> Its just so much easier to do with any accuracy. Mixer boards are designed
> this way... well at least they were in the seventies when I was getting
> trained in such things. Digital mixers are of coarse all math.
Ok; well, if that is true, then your ideas make sense - it is better to
avoid the boost if possible.
We don't know how to tell that though. From what we can read from the
hardware, it is the same slider that can either attenuate or amplify.
It might also be that your chip is designed that way but other chips are
not. Might be worth conducting a larger test (i e testing different
kinds of hardware) to see which setting gives higher quality in general.
David Henningsson, Canonical Ltd.
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