Dne 15.1.2018 v 14:49 Ricard Wanderlof napsal(a): > > On Mon, 15 Jan 2018, Takashi Iwai wrote: > >>> Ok, my suggestion would be set MAX_DB_UPPER_LIMIT to 90 dB. 90 dB comes >>> out as 31622, which still is manageable when shifted up by VOL_SCALE_SHIFT >>> (= 16), fitting in a 32-bit int. Thus it works in MULTI_DIV_short() too, >>> where it is multiplied with the 16-bit sample value yielding an int. >>> >>> I'll try it out and prepare a patch. >> >> Well, but +90dB gain doesn't look like a normal usage pattern. Why do >> you have to use softvol plugin for achieving that specific purpose? > > The usecase we have actually calls for 55 dB of gain maximum, but I was > thinking that looking at the code the maths can actually handle 90 dB so > it would be good 'reasonable limit' - it's a nice round number and fits in > 16 bits (signed). > > The usecase we have is using digital MEMS microphones ((2S connected, > with no integral amplification) and when the sound source is far away, a > fair amount of gain can be needed. Wow, the signal quality from few bits per sample must be really good ;-) It would be better to use ADC with higher resolution (24-bit) and low noise floor (but I see the possible costs requirements). This is why we have such good audio in collaborative conferences :-) Jaroslav -- Jaroslav Kysela <perex@xxxxxxxx> Linux Sound Maintainer; ALSA Project; Red Hat, Inc. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
