Re: [Alsa-user] Audigy2 recording level much too low - an (one and half) year later

[James Courtier-D. <Ja...@su...>]

Zbigniew Baniewski wrote:
> Hallo,
> 
> Over a year ago I've reported the problem with very low microphone input
> sensitivity, while recording using Audigy2, what is making this card unusable
> for VoIP.
> 
> At that time, I've received a tip (thanks again), to fix it by introducing
> a line:
> 
>     snd_ac97_write_cache(emu->ac97, AC97_REC_GAIN, 0x0f0f);
> 
> ...directly after a line:
> 
>     snd_ac97_write_cache(emu->ac97, AC97_REC_SEL, 0x0000);
> 
> ...in sound/pci/emu10k1/emumixer.c
> 
> Yes, this works OK. So why not introduce this line for steady, in every ALSA
> release? The problem is, that while there are binaries for kernel available,
> one has to patch, then compile every new kernel version again and again.
> 
> Couldn't be possible to insert this line into emumixer.c for steady?
> I suppose, that every Audigy2 user will be grateful for making this. Even,
> if it can be treated as "temporary hack", there could be placed a remark
> in the code, like f.e.: "temporary fix, will be changed in the future". I'm
> patching those kernels over a year - and this "temporary" fix doesn't seem
> to spoil anything.
> 
> Keeping the broken micro-input handling - and not doing with this anything
> since years - doesn't seem to have much sense. So why not fix it at least
> such way, when it _just works_, and it's tested (at least by me)?

It is a levels problem.
Mic captures at 24bits.
The DSP handles 24bits fine.
When the sound is passed from the DSP to the CPU only the top 16bits of
the 24bit value are passed. This accounts for the low capture levels.
The "snd_ac97_write_cache(emu->ac97, AC97_REC_GAIN, 0x0f0f);" reduces
the analogue capture headroom so is not ideal.
I think a better fix would be to add DSP code to adjust the 24bit value
into 16bits.
The current 24bit to 16bit conversion introduces about 48 dB loss.